Free to Access Metocean Glossary

Summary of Metocean Terms from Various Source by BW Geohydromatics

(SC | 05/05/2021)

With the increasing need for industry to understand the terms frequently used in the world of meteorology and oceanography (metocean), BW Geohydromatics launched the Metocean Glossary which can be accessed for free. The experience of BW Geohydromatics, a dozen years of consultancy in the metocean field, is condensed in a Glossary designed to optimize support to the industry.

This glossary is a reference dictionary of hydrographic terms used in various standards, specifications, and other information frequently used by the maritime industry. Here you can find more than 6,500 easy-to-understand descriptions of meteorological and oceanographic terms.

With this Glossary, the industry, especially our clients, will be made easy to understand Metocean’s scientific terms which sometimes also have many confusing acronyms.

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Glosarium Metocean

Rangkuman Istilah dalam Dunia Metocean dari Berbagai Sumber oleh BW Geohydromatics

Dengan meningkatnya kebutuhan industri untuk memahami istilah yang sering dipakai di dunia meteorologi dan oseanografi (metocean), BW Geohydromatics meluncurkan Glosarium Metocean yang dapat diakses secara gratis. Pengalaman BW Geohydromatics, yang selama belasan tahun menjadi konsultan di bidang metocean, dipadatkan dalam Glosarium yang dirancang untuk mengoptimalkan dukungan kepada industri.

Glosarium ini adalah kamus referensi istilah terkait hidrografi yang digunakan dalam berbagai standar, spesifikasi, dan informasi lain yang sering digunakan industri maritim. Di sini dapat ditemukan lebih dari 6500 penjelasan istilah meteorologi dan oseanografi yang mudah untuk dipahami.

Dengan Glosarium ini, dunia industri, terutama para klien, akan sangat dimudahkan dalam memahami istilah Metocean yang ilmiah dan memiliki banyak akronim.

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Metocean Glossary

Metocean glossary is a dictionary that is authoritative reference to hydrographic related terms and definitions used in various standards, specifications and other informative referred in Maritime Industry. In Indonesian hydrography, The International Hydrographics Dictionary (S-32) is the main standards of terms and definition used.

Please use the relevance 2-3 words from the desired term to get the best result from our search feature.
Example: to find HAT refering to Tidal Level, please type “HAT Tidal Level” in the search box:

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ID	TERM	DEFINITION
1	Point	One thirty-second of a circle, or 11 1/4 degrees. Also called compass point when used in reference to compass directions. The extreme end of a cape; or the outer end of any land area protruding into the water, usually less prominent than a cape. In digital cartography, the 0-dimensional geometric primitive of an object that specifies location. [14]
2	Time	The measurable aspect of duration. The hour of the day reckoned by the position of a celestial reference point relative to a reference celestial meridian. An elapsed interval. [14]
3	Ice	The solid form of water. [14]
4	Surf	Collective term for breakers. The wave activity in the area between the shoreline and the outermost limit of breakers. [14]
5	Ria	A long narrow inlet, with depth gradually diminishing inward; a creek. Any broad river opening into the ocean. [14]
6	Gat	A natural or artificial passage or channel through shoals or steep banks, or across a line of banks lying between two channels. [14]
7	Wave	A disturbance which moves through or over the surface of the medium with speed dependent upon the properties of the medium. A ridge deformation, or undulation of the surface of a liquid. [14]
8	Light	A luminous or lighted aid to navigation. For internationally agreed abbreviations of light characteristics see the international chart specifications. [14]
9	Earth	The planet which we inhabit. The solid matter of the globe in distinction from water and air. The ground. [14]
10	Area	In united nations law of the sea terminology the seabed and ocean floor and subsoil thereof, beyond the limits of national jurisdiction. [14]
11	Plan	An orthographic drawing on a horizontal plane, as of an instrument, a horizontal section, or a layout. A large-scale map or chart of a small area. [14]
12	Chart	A special-purpose map generally designed for navigation or other purposes. See chart: nautical, paper. [14]
13	Phot	The unit of illumination in the cgs system. [14]
14	Position	Data which define the location of a point with respect to a reference system. The coordinates which define such a location. The place occupied by a point on the surface of the earth, or in space. [14]
15	Lane	An established route as an air lane or shipping lane. In an electronic radiolocation lattice, the zone between two lines on which measured values, expressed in terms of the system's electronic unit (wavelength or microsecond), are whole numbers and are one unit apart. See lattice. A lead. [14]
16	Tide	The periodic rise and fall of the surface of oceans, bays, etc., due principally to the gravitational interactions between the moon, sun, and earth. [14]
17	Survey	The orderly process of determining data relating to the physical or chemical characteristics of the earth. The act or operation of making measurements for determining the relative position of points on, above or beneath the earth's surface. The result of such operations. An organization for making surveys. [14]
18	Rate	In electronic navigation, the designation of pulse repetition rate for a pair of transmitting stations, their signals, and the resulting lines of position. [14]
19	Magnet	A body which produces a magnetic field around itself. It has the property of attracting certain materials capable of being magnetized. See heeling magnet. [14]
20	Direction	In surveying and mapping, the angle between a line or plane and an arbitrarily chosen reference line or plane. [14]
21	Rod	A unit of length equal to 5.5 yards or 16.5 feet. Also called perch or pole. A stadia or levelling rod. See also sounding pole. [14]
22	Horizon	In general, the apparent or visible junction of the earth and sky, as seen from any specific position. [14]
23	Sound	(v.i.). To measure the depth of the water. [14]
24	Sound	A relatively long arm of the sea forming a channel between an island and a mainland or connecting two larger bodies of water, as a sea and the ocean, or two parts of the same body but usually wider and more extensive than a strait. A vibratory disturbance in air or some other elastic medium, capable of being heard by the human ear, and thus of any frequency between about 20 and 20,000 cycles per second. [14]
25	Log	(v.t.). Said of a ship moving at a specified speed according to the indications given by the log. [14]
26	Log	An instrument for measuring the speed or distance or both travelled by a vessel. [14]
27	High	See anticyclone. [14]
28	Level	(v.t.). To make perfectly horizontal by means of a level. [14]
29	Level	A horizontal plane or line; especially, such a plane taken as a basis for the measurement of elevati-on. See sea level, mean sea level, half tide level, still water level. A level tract of land; a stretch of country approximately horizontal and unbroken by elevations. In surveying and levelling, either a spirit level or a levelling instrument. [14]
30	Pass	A break in a mountain range, permitting easier passage from one side of the range to the other; also called a col. A navigable channel leading to a harbor or river. Sometimes called passage. A narrow connecting channel between two bodies of water. [14]
31	Col	A marked depression in the summit line of a mountain chain, generally affording a pass from one slope to the other. In meteorology, a saddle-backed region of almost uniform pressure which appears between two depressions and two anticyclones arranged alternately in a cross. [14]
32	Meter	(1) a person who measures. (2) an instrument or apparatus for measuring. (3) a device for measuring a specified thing as in thermometer or barometer. See also metre. [14]
33	Current	Water or other fluid in essentially horizontal motion. In British terminology, a non-periodical movement of water, generally horizontally, due to many causes such as different temperatures and prevalent winds. Some may be temporary, others permanent. [14]
34	Wind	Air motion relative to the earth's surface. Unless it is otherwise specified, only the horizontal component is considered. [14]
35	Depth	The vertical distance from a given water level to the bottom. [14]
36	Station	Generally, a permanent or temporary location where scientific observations and measurements are made. In surveying, a point whose position has been (or is to be) determined. A station may be a marked station (i.e., a point permanently marked for recovery) or an unmarked station, one which is not recoverable. Also called survey station. [14]
37	Ram	The underwater projection of ice from an ice front, ice wall, iceberg, or floe. [14]
38	Port	A place provided with terminal and transfer facilities for loading and discharging cargo or passengers, usually located in a harbor. The left side of a craft, facing forward. The opposite is starboard. [14]
39	Sphere	A curved surface all points of which are equidistant from a fixed point within, called the center. [14]
40	Land	The solid portion of the earth's surface, as opposed to sea, water. A part of the earth's surface marked off by natural or political boundaries. [14]
41	Ocean	The vast body of water on the surface of the globe, which surrounds the land, the main or great sea. One of the main areas into which this body of water is divided geographically. [14]
42	Rig	A temporary, mobile structure, either fixed or floating, used in the exploration stages of oil and gas fields. [14]
43	Mark	One of the bits of leather, cloth, etc. Indicating a specified length of a lead line. A charted conspicuous object, structure, or light serving as an indicator for guidance or warning of a craft; a beacon. A definite object, such as an imprinted metal disk, used to designate a survey point and sometimes refers to the entire survey monument. Mark is used with a qualifying term such as station, reference, azimuth, or bench. See also benchmark and reference mark. [14]
44	EVA	Extreme value analysis (EVA) ; A statistical tool to estimate the likelihood of the occurrence of extreme values based on a few basic assumptions and observed/measured data. [7]
45	Navigation	The process of directing the movement of a craft from one point to another. [14]
46	Vertical	(Adj.). In the direction of gravity; perpendicular to the plane of the horizon. [14]
47	Vertical	(n.). The direction in which the force of gravity acts. A vertical line, plane, etc. [14]
48	Circle	In a surveying instrument, the graduated disk which is perpendicular to and centered about an axis of rotation and is calibrated to read the amount of rotation. [14]
49	Signal	As applied to electronics, any transmitted electrical impulse. That which conveys intelligence in any form of communication, such as a time signal, a pip on the scope of electronic equipment, or an object marking the location of a surveying station. [14]
50	Photograph	A general term for a positive or negative picture made with a camera on sensitized material or prints from such a camera original. [14]
51	Base	In a triangulation, the side of one of a series of connected triangles, the length of which is measured directly and with prescribed accuracy and precision, and from which the lengths of the other triangle sides are obtained by computation. Also called base line or triangulation base line. See also base terminals. [14]
52	Sun	The luminous celestial body at the center of the solar system, around which other celestial bodies revolve. [14]
53	Erg	The unit of energy or work in the cgs system. [14]
54	Scale	A series of marks or graduations at definite intervals. The ratio between the linear dimensions of a chart, map, drawing, etc., and the actual dimensions represented. It may be called chart scale or map scale when applied to a chart or a map. In photogrammetry, the ratio of a distance on a photo-graph to a corresponding distance on the ground. The scale of a photograph varies from point-to-point because of displacements caused by tilt and relief; but it is usually taken as f/h where f is the principal distance of the camera and h is the height of the camera above mean ground elevation. [14]
55	Range	Two or more objects in line. Such objects are said to be in range. An observer having them in range is said to be on the range. See also transit. Distance in a single direction or along a great circle. The extreme distance at which an object or light can be seen, or a signal detected or used. The distance a craft can travel without refueling, usually called cruising radius. The difference in extreme values of a variable quantity. [14]
56	Radio	Communication by electromagnetic waves, without a connecting wire. A radio receiver. Sometimes called wireless particularly in British terminology. [14]
57	Mount	A large hill or mountain, usually a detached, characteristically conical mass of earth. The term 'mount' is always used instead of mountain when it precedes a proper name. [14]
58	Height	the vertical distance of the top of an object affixed to the surface of the earth, measured from a specified datum usually a high-water datum. - 2. The vertical dimension of an object. Also called vertical length. [14]
59	Map	(v.t.). To prepare a map or engage in a mapping operation. [14]
60	Map	A representation (usually on a flat medium) of all or a portion of the earth or other celestial body, showing the relative size and position of features to some given scale or projection; also, a representation of all or part of the celestial sphere. A map may emphasize, generalize, or omit the representation of certain features to satisfy specific requirements. Maps are frequently categorized and referred to according to the type of information which they are primarily designed to convey, to distinguish them from maps of other types. [14]
61	Ground	The bottom of the sea. The solid surface of the earth. [14]
62	Ground	(v.t.). To touch bottom or run aground. See strand. [14]
63	Bottom	Any ground covered by water. [14]
64	Meridian	A north-south reference line, particularly a great circle through the geographical poles of the earth, from which longitudes (or departures) and azimuths are reckoned; or a plane normal to the geoid or spheroid defining such a line. The term usually refers to the upper branch. [14]
65	Fix	(v.t.). In hydrographic surveying, to determine, at regular intervals, the position of ships or boats, while sailing along a line of sounding. The usual method of fixing hydrographic surveys within sight of land is the three-point fix method. [14]
66	Period	The interval needed to complete a cycle. Any specified duration of time. [14]
67	Sounding	Measured or charted depth of water, or the measurement of such a depth. In meteorology, determination of one or several upper air meteorological elements by means of instruments carried up by balloon, aircraft, kite, glider, rocket, satellite, etc. [14]
68	Horizontal	(adj). Parallel to the plane of the horizon; perpendicular to the direction of gravity. [14]
69	Fix	In navigation, a relatively accurate position determined without reference to any former position. It may be classed as visual, celestial, electronic, etc., depending upon the means of establishing it. [14]
70	Buoy	A floating object moored to the bottom in a particular (charted) place, as an aid to navigation or for other specific purposes. Navigational buoys may be classified according to: (a) their shape, appearance, or construction, such as barrel, can, cask, conical, cylindrical, dan, keg, nun, pillar, spar, spherical, or top mark buoy; (b) their colour, such as black, cheque red, green, red buoy; (c) their location, such as bifurcation, fairway, junction, mid-channel, middle-ground, or turning buoy; (d) the various kinds of hazards or dangers to navigation which they mark, such as bar, isolated danger, fish trap, obstruction, spoil ground, telegraph or wreck buoy; (e) their particular purpose or use, such as anchor, anchorage, compass adjustment, dredging, farewell (or landfall), marker, quarantine, station (or watch), or warping buoy. [14]
71	Data	A representation of facts, concepts, or instructions in a formalized manner suitable for communication, interpretation, or processing. [14]
72	Axis	The line, real or imaginary, about which something centers or revolves. [14]
73	Temperature	The intensity or degree of heat. [14]
74	Tie	A survey connection from a point of known position to a point whose position is desired. A tie is made to determine the position of a supplementary point whose position is desired for mapping or reference purposes, or to close a survey on a previously determined point. To tie in is to make such a connection. The point to which the connection is made is termed a tie point. [14]
75	Image	The optical counterpart of an object. [14]
76	Mil	1. 1/6400 of the circumference of a circle. Approximately 1/1000 radian. 2. 1/1000 of an inch. [14]
77	Error	The difference between an observed or computed value of a quantity and the ideal or true value of that quantity. [14]
78	Compass	An instrument consisting of two legs jointed by a pivot used for describing circles or transferring measurements. Also referred to as pair of compasses. An instrument for indicating a horizontal reference direction relative to the earth. [14]
79	Table	An orderly, condensed arrangement of numerical or other information, usually in parallel vertical columns. See conversion table, current tables, tide tables, traverse table. [14]
80	Observation	The act or practice of noting and recording facts and events as for some scientific study. The measure of a quantity whose value is desired. The data so noted and recorded. A single measure, at a single setting of an apparatus. [14]
81	Shore	The narrow strip of land in immediate contact with any body of water including the area between high and low water lines. [14]
82	Speed	Rate of motion. The terms speed and velocity are often used interchangeably, but speed is a scalar, having magnitude only, while velocity is a vector quantity, having both magnitude and direction. Speed may either be the ship's speed through water, or the speed made good over ground. [14]
83	Control	A system of points with established positions or elevations, or both, which are used as fixed references in positioning and correlating map features. Control is generally classified in four orders (with first order denoting highest quality) according to the precision of the methods and instruments used in establishing it, and the accuracy of the resultant positions and elevations. Often called basic control. Regulation or direction of a machine, electronic equipment, etc.; or the dial, knob, switch, etc. For performing this function. The exercise of directing influence over the movements of a craft or missile, with reference to changes in direction and speed. [14]
84	Echo	Reflected radiant energy. [14]
85	Gravity	That force which tends to pull bodies towards the earth; that is to give bodies weight. Gravity is the resultant of two opposing forces: gravitation and centrifugal force due to the rotation of the earth. [14]
86	Down	An area of high, treeless ground, usually undulating and covered with grass. See also dune. [14]
87	Plate	A thin, metal, plastic, or paper sheet, that carries the printing image and whose surface is treated to make only the image areas ink receptive. [14]
88	Disc	Rotating storage medium composed of one or two usable surfaces or a vertical assembly of such discs with a common axis. Typically, discs combine high storage volumes and short access time allowing fast access to data which is distributed randomly over the medium. [14]
89	Sextant	A double-reflecting instrument for measuring angles, primarily altitudes of celestial bodies. The sextant has an arc of 60°, a sixth of a circle, from which it derives its name, and a range of 120°. In modern practice the term also applies to a similar instrument, regardless of its range. See also octant, quadrant and quintan. [14]
90	Transit	In astronomy, the apparent passage of a star or other celestial body across a defined line of the celestial sphere, as a meridian, prime vertical, or almucantar. When no line is specified, a transit across the meridian is usually intended. See meridian transit. The apparent passage of a star or other celestial body across a line in the reticle of a telescope, or some line of sight. The apparent passage of a smaller celestial body across the disk of a larger celestial body. A surveying instrument composed of a horizontal circle graduated in circular measure and an alidade with a telescope which can be reversed in its supports without being lifted therefrom. Also, the act of making such a reversal. A theodolite having a telescope that can be transited in its supports is a transit and is sometimes termed a transit theodolite. All modern theodolites are transits. An astronomical instrument having a telescope which can be so adjusted in position that the line of sight may be made to define a vertical circle. A transit used in astronomical work is usually termed either an astro-nomic(al) transit or a transit instrument. In navigation, the position of two distant, fixed objects when they are in line to an observer; the line passing through them and the observer being a line of position. See also range. [14]
91	Lock	A wet dock in a waterway, permitting a ship to pass from one level to another. See tide lock. [14]
92	Second	The unit of time in the si system. A sixtieth part of a minute, an angle, or an arc. [14]
93	Ton	A unit of weight equal to 1,000 kilograms ('metric ton'), 2,240 pounds ('long ton'), or 2,000 pounds ('short ton'). [14]
94	Phase	The visible aspect of an object. The amount by which a cycle has progressed from a specified origin. In astronomy, any of the stages of variation in the illumination of the moon or a planet. See phase(s) of the moon. In physics, the state of aggregation of a substance, for example, solid (ice), liquid (water), or gas (vapor). [14]
95	Beacon	A fixed artificial navigation mark that can be recognized by its shape, colour, pattern, top mark or light character, or a combination of these. It may carry various additional aids to navigation. This term is not commonly used when the navigation mark can be classified as a lighthouse. [14]
96	Run	A brook, or small creek. The distance travelled by a craft during any given time interval, or since leaving a designated place. Complete performance of one programme on a computer. [14]
97	Crib	A permanent marine structure usually designed to support or elevate pipelines; especially a structure enclosing a screening device at the offshore end of a potable water intake pipe. The structure is commonly a heavy timber enclosure that has been sunken with rocks or other debris. [14]
98	Vent	The orifice through which molten lava reaches the crater of a volcano. Eventually it may become choked as the lava solidifies to form a plug or neck. [14]
99	Degree	A unit of angular or circular-arc measurement, equal to 1/360 of a circle. A unit of measurement of temperature in any scale. [14]
100	Parallax	An apparent displacement of the position of a body with respect to a reference point or system, caused by a shift in the point of observation. [14]
101	Fog	Suspension of very small water droplets in the air, generally reducing the horizontal visibility at the earth's surface to less than 1 kilometre. [14]
102	Cast	In oceanography, a single lowering of a series of water bottles or other oceanographic instruments at an oceanographic station. Also referred to as oceanographic cast. [14]
103	Flat	A level tract of land, as the bed of a dry lake or an area frequently uncovered at low tide. Usually in plural. [14]
104	Track	(v.t.). To follow the movements of an object as by radar or an optical system. To navigate by keeping a record, tabular or graphical of the past positions of a craft without regard for future positions. [14]
105	Track	The actual path or route of a craft over the ground or sea bottom, or its graphic representation. In air navigation also called track made good. [14]
106	Standard	An exact value (a physical entity or an abstract concept) established and defined by authority, custom, or common consent, to serve as a reference, model, or rule in measuring quantities or qualities, establishing practices or procedures, or evaluating results. In chart construction, a master copy of a chart upon which are marked all corrections affecting the chart between printings. [14]
107	Edge	In topography, the crest of a sharply pointed ridge. [14]
108	Front	N meteorology: a) surface of separation of two air masses (frontal surface); b) line of intersection of the surface of separation of two air masses with another surface or with the ground. [14]
109	Spheroid	An ellipsoid; a figure resembling a sphere. Also called ellipsoid or ellipsoid of revolution, from the fact that it can be formed by revolving an ellipse about one of its axes. In geodesy, this term is fre-quently used to mean reference spheroid. See also spheroid: oblate and spheroid: prolate. [14]
110	Name	The label of a numerical value used particularly to refer to the n (north) or s (south) label of latitude and declination. When latitude and declination are both n or both s, they are said to be of the same name, but if one is n and the others, they are said to be of contrary name. [14]
111	Channel	That part of a body of water (sometimes dredged) deep enough for navigation through an area otherwise not navigable. It is usually marked by a single or double line of buoys and sometimes by ranges. The deepest part of a stream, bay, or strait through which the main current flows. See also strait. [14]
112	Grid	A series of lines, usually straight and parallel, superimposed on a chart or plotting sheet to serve as a directional reference for navigation. See also graticule. Two sets of mutually perpendicular lines dividing a map, chart, or other representation of the earth's surface, into squares or rectangles to permit location of any point by a system of rectangular coordinates. In electronics, an electrode with one or more openings to permit passage of electrons or ions. [14]
113	Sand	Loose material consisting of small but easily distinguishable, separate grains, between 0.0625 and 2.000 millimeters in diameter. [14]
114	Group	A term distinguishing a light exhibiting two or more flashes or occultations from one exhibiting a single flash or single occultation. [14]
115	Longitude	Angular distance, along a primary great circle, from the adopted reference point. One of coordinates used to describe a position the other being latitude. [14]
116	Month	A measure of time based on the motion of the moon in its orbit. [14]
117	Tape	In surveying, a ribbon of steel, invar, or other suitable material on which graduations are placed for the measurement of lengths or distances. See also base tape (or wire). [14]
118	Hole	An abrupt hollow in the ground or ocean floor. See also passage. [14]
119	Clear	(v.t.). To make such distance from an object as to have open sea-room. [14]
120	Reach	A straight section of a river, especially a navigable river between two bends. See also sea reach. An arm of the sea extending into the land. [14]
121	Shallow	(Adj.). Having little depth. [14]
122	Shallow	(n.). An area composed of unconsolidated material where the depth of water is relatively slight. It may be a hazard to surface navigation. [14]
123	Thunder	Sharp or rumbling sound which accompanies lightning. [14]
124	Orbit	The path of a body or particle under the influence of a gravitational or other force. For instance, the orbit of a celestial body is its path relative to another body around which it revolves. In water waves, the path of a water particle affected by the wave motion. [14]
125	Density	In photography, a measure of the degree of blackening of an exposed film, plate or paper after development, or the direct image (in the case of a print-out material). It is defined strictly as the logarithm of the optical opacity. In oceanography, density is equivalent to specific gravity and represents the ratio, at atmospheric pressure, of the weight of a given volume of sea water to that of an equal volume of distilled water at 4.0°c. [14]
126	Rotation	Turning of a body about an axis within the body, as the daily rotation of the earth. See revolution. [14]
127	Component	See harmonic constituent. [14]
128	Tidal Current	See current. [14]
129	Beam	Radiant energy confined to a particular shape. [14]
130	Ais	See automatic identification system [14]
131	Iec	International electrotechnical commission [14]
132	Lag	The delay between change of condition and the indication of the change on an instrument. Delay in human reaction. The amount one cyclic motion is behind another, expressed in degrees. The opposite is lead. [14]
133	Great Circle	See circle. [14]
134	Slope	The deepening sea floor out from the shelf edge to the upper limit of the continental rise, or the point where there is a general decrease in steepness. [14]
135	Planet	A celestial body of the solar system, shining by reflected light and revolving around the sun. [14]
136	Negative	A photographic image on film, plate, or paper, in which the subject tones to which the emulsion is sensitive are reversed or complementary. [14]
137	Deviation	See deviation: magnetic. [14]
138	Telescope	An optical instrument used as an aid in viewing or photographing distant objects, particularly celestial objects. [14]
139	Gain	The ration of output voltage, current or power to input voltage, current, or power in electronic instruments. [14]
140	Heat	A form of energy transferred between systems by virtue of their temperature differences. [1]
141	Sample	A representative part or single item from a larger whole or group especially produced for inspection or to give evidence of quality. [14]
142	Accuracy	The extent to which a measured or enumerated value agrees with the assumed or accepted value. See precision. [14]
143	Word	An addressable subdivision of storage memory of a computer system. Usually an integer number of bytes (e.g., 4 bytes = 32 bit) indicating the standard length of number representation in storage. [14]
144	Cable	A unit of distance originally equal to the length of a ship's anchor cable, but now generally considered to be about 600 feet. In the British navy it is 608 feet, or exactly one-tenth of a nautical mile. In the united states navy, it is 720 feet but is infrequently used. Sometimes called cable length. A chain or very strong fibre or wire rope used to anchor or moor vessels or buoys. A stranded conductor or an assembly of two or more electric conductors insulated from each other, but laid up together with a strong, waterproof covering. [14]
145	Shoal	(Adj.). Shallow. [14]
146	Shoal	(n.). An offshore hazard to surface navigation with substantially less clearance than the surrounding area and composed of unconsolidated material. [14]
147	Shoal	(v.i.). To proceed from a greater to a lesser depth. To cause to become less deep. [14]
148	Sight	Observation of the altitude, and sometimes also the azimuth of a celestial body for a line of position, or the data obtained by such observation. Any of various devices used to aid the eyes in lining up an optical instrument on its objective. [14]
149	Climate	Fluctuating aggregate of atmospheric conditions characterized by the states and developments of the weather of a given area. [14]
150	Traverse	A method of surveying in which a sequence of lengths and directions of lines between points on the earth are obtained from field measurements and used in determining positions of the points. Also called survey traverse. [14]
151	Velocity	A vector quantity equal to speed in a given direction. [14]
152	Radiation	Emission or transfer of energy in the form of electromagnetic waves or particles. The energy itself is also termed radiant energy. [14]
153	Path	A line of movement; course taken, as the path of a meteor. A line connecting a series of points in space and constituting a proposed or travelled route. [14]
154	Celestial Body	Anybody pertaining to the heavens, constituting a unit for astronomical study, such as the sun, the moon, the planets, fixed stars, comets, etc. Also called heavenly body. [14]
155	Dam	A barrier to check or confine anything in motion; particularly one constructed to hold back water and raise its level to form a reservoir, or to prevent flooding. [14]
156	Dip	The vertical angle, at the eye of an observer between the horizontal and the line of sight to the apparent horizon. Also called dip of the horizon or depression of the horizon. The angle between the horizontal and the lines of forces of the earth's magnetic field at any point. Also called magnetic dip or magnetic inclination. [14]
157	Matte	Conglomerate of sand, mud and seaweed forming a shoal or reef. [14]
158	Island	A piece of land surrounded by water. [14]
159	Drawing	The graphic representation of data on a non-volatile medium. An impression following the printing of a nautical chart of either its black or its magenta detail on matte finish transparent plastic, used in revising subsequent printings of the chart. [14]
160	Contrast	In photography, the actual difference in density between the highlights and the shadows on a negative or positive. Contrast is not concerned with the magnitude of density but only with the difference in densities. Also, the rating of a photographic material corresponding to the relative density difference which it exhibits. [14]
161	Sediment	Particulate organic and inorganic matter which accumulates in a loose unconsolidated form. It may be chemically precipitated from solution, secreted by organisms, or transported by air, ice, wind, or water and deposited. [14]
162	Test	The hard covering or supporting structure of many invertebrates; it may be enclosed within an outer layer of living tissue; a shell. [14]
163	Clock	Instrument for measuring time and recording hours. [14]
164	Radian	The unit of plane angles in the si system. [14]
165	Acoustic	Science of sound, including its production, transmission, and effects. [14]
166	Magnetism	The ability to attract magnetic material, notably iron and steel. [14]
167	Thermometer	Instrument used in the measurement of temperature. [14]
168	Ebb	The ebb streams. Sometimes the term 'ebb' is also used with reference to vertical tidal movement. The opposite is flood. [14]
169	Power	See magnifying power. [14]
170	Heading	The direction in which a vessel or craft is pointed, usually expressed in degrees from north (true, magnetic, or compass) [14]
171	Passage	A narrow navigable channel, especially one through reefs or islands. [14]
172	Sailing	A method of solving the various problems involving course, distance, difference of latitude, difference of longitude and departure. The various methods are collectively spoken of as 'the sailings'. [14]
173	Harmonic	A sinusoidal quantity having a frequency that is an integral multiple of the frequency of a periodic quantity to which it is related. [14]
174	Positive	In photography, an image of the original object which corresponds to the same in the scheme of light and shade. [14]
175	Core	The central or innermost part of anything. See centrosphere. In oceanography, a vertical, cylindrical sample of the bottom sediments from which the nature and stratification of the bottom may be determined. Also, called core sample or sediment core. [14]
176	Crest	The highest part of a wave, swell, ridge, etc. [14]
177	Flood	The flood streams. Sometimes the term 'flood' is also used with reference to vertical tidal movement. The opposite is ebb. An overflowing of water on land usually dry; inundation. [14]
178	Minute	The sixtieth part of an hour; sixty seconds. The sixtieth part of a degree of arc; sixty seconds. [14]
179	Relief	The elevations or the inequalities, collectively, of a land surface; represented on a map or chart by contours, hypsometric tints, shading, spot elevations, hachures, etc. [14]
180	Deposit	Accumulations of solid material (of any type or from any source) on the sea bottom which eventually may become compacted and consolidated and form sedimentary rock. [14]
181	Computer	A person who performs calculations. A device capable of accepting data, processing it according to stored instruction that are followed in automatic sequence, and supplying the results in some form. It usually consists of input and output devices, storage, arithmetic and logical units, and a control unit. [14]
182	Junction	Place of meeting or joining, as that of a tributary with a main river, or of two channels in a waterway. In levelling, the place where two or more lines of levels are connected together. In hydrographic survey, the joining of two adjacent survey sheets. See overlap. [14]
183	Mountain	A natural elevation of the earth's surface rising abruptly from the surrounding level, and attaining an altitude which, relatively to adjacent elevations, is impressive or notable. [14]
184	Intersection	In surveying, the procedure of determining the horizontal position of an unoccupied point (intersec-tion station) by direction observations from two or more known positions. In photogrammetry, the procedure of determining the horizontal position of a point by intersecting lines of direction obtained photogrammetrically. The lines of direction may be obtained directly from vertical photographs or by graphic or mathematical rectification of tilted photographs. [14]
185	Dial	The face of a watch or clock. The clockwise face of an instrument for indicating, as by a moving pointer, the amount of something; face of a compass, gauge, or meter. A sundial. [14]
186	Mile	A unit of distance. See international nautical mile, sea mile, statute mile. [14]
187	Paper	For printing hydrographic charts, heavyweight, single layer paper is used. Such paper is generally made wholly or partly from rags and simulates hand-made paper. It is strong, moisture resistant and manufactured to withstand surface erasure. [14]
188	Signi	Abbreviation for signalization de navigation instruments. A system of buoyage used in certain inland waters in the Netherlands. [14]
189	Vector	Direct connection between two points, either given as two sets of coordinates (points), or by direction and distance from one given set of coordinates; or a point in a vector space defined by one set of coordinates relative to the origin of a coordinate system. [14]
190	Cyclone	See depression. [14]
191	Offshore	(Adj. And adv.). Away from the shore. [14]
192	Offshore	(n.). The comparatively flat zone of variable width which extends from the outer margin of the rather steeply sloping shoreface to the edge of the continental shelf. [14]
193	Navigational	(Adj.). See nautical. [14]
194	Bank	an elevation of the sea floor over which the depth of water is relatively shallow. [14]
195	Gyro	See gyroscope. [14]
196	Snow	Precipitation of ice crystals, most of which are branched (sometimes starshaped). [14]
197	Shelf	Geologically an area adjacent to a continent or around an island and extending from the low-water line to the depth at which there is usually a marked increase of slope towards greater depth. See also continental shelf. [14]
198	Spring	Spring tide. A natural issue of water or other substances from the earth. One on the bottom of the sea is called a submarine spring. [14]
199	Weight	The force with which a body is attracted by gravity. Any block or mass of material used for its heaviness. The relative value of an observation, source, or quantity when compared with other observations, sources, or quantities of the same or related quantities. The value determined by the most reliable method is assigned the greatest weight. [14]
200	Seaward	(Adj. And adv.). Away from the land; toward the sea. [14]
201	Gradient	The change of any quantity with distance in any given direction. See pressure gradient, temperature lapse rate. The amount of slope, inclination to the horizontal, in road, railway, etc. [14]
202	Leg	Each straight section of a traverse. One part of a craft's track consisting of a single course line. [14]
203	Hill	A small, isolated elevation, smaller than a mountain. See also knoll. [14]
204	Lake	A large body of water surrounded by land. [14]
205	Rift	A cleft, fissure, or chasm in the earth. See median valley. [14]
206	Zenith	The point where the direction of the plumb line produced above the horizon meets the celestial sphere. [14]
207	Astronomy	The science which deals with the size, constitution, motions, relative positions, etc. Of celestial bodies, including the earth. See also astrometry. [14]
208	Refraction	The process in which the direction of energy propagation is changed as the result of a change in density within the propagating medium, or as the energy passes through the interface representing a density discontinuity between two media. [14]
209	Straight Line	Mathematically the line of shortest distance between two points in a specified space or on a specified surface. [14]
210	Bay	Wide indentation in the coastline generally smaller than a gulf and larger than a cove. For the purposes of the united nations convention on the law of the sea, a bay is a well-marked indentation whose penetration is in such proportion to the width of its mouth as to contain land locked waters and constitute more than a mere curvature of the coast. See also historic bay. [14]
211	Card	See compass card. [14]
212	Lash	See lighter aboard ship. [14]
213	Moor	(v.t.). To secure a boat or other floating thing to a fixed object or the sea bottom. [14]
214	Tilt	The angle which anything makes with the horizontal. In photogrammetry, the angle at the perspective center between the photograph perpendicular and the plumb line, or other exterior reference direction; also, the dihedral angle between the plane of the photograph and the horizontal plane. [14]
215	Nadir	That point on the celestial sphere directly beneath the observer, and directly opposite to the zenith. [14]
216	Antenna	A conductor or system of conductors for radiating or receiving radio waves. Also called aerial. [14]
217	Pattern	See lattice. [14]
218	Sounder	A machine or apparatus for sounding. An echo sounder. [14]
219	Tornado	In north America, the name for an intense spout of large diameter. [14]
220	Boundary	Anything marking a limit; bound; border. [14]
221	Sea Floor	The bottom of the ocean and seas where there is a generally smooth gentle gradient. Also referred to as seabed (sometimes seabed or sea-bed), and sea bottom. [14]
222	Sea Water	The water of the seas, distinguished from fresh water by its appreciable salinity. The degree of the salinity greatly affects the water's physical characteristics. [14]
223	Magnetometer	An instrument for measuring the intensity and/or the direction of the earth's magnetic field. [14]
224	Etch	(v.t.). To form an image within the surface of a printing or drawing material by the use of solvents. [14]
225	Reef	A mass of rock or coral which either reaches close to the sea surface or is exposed at low tide, posing a hazard to navigation. [14]
226	Ridge	The linked major mid-oceanic mountain systems of global extent. Also called mid-oceanic ridge. [14]
227	Maritime	Bordering on, concerned with, or related to the sea. [14]
228	Original	See reproduction. [14]
229	Surround	See margin. [14]
230	Constituent	See harmonic constituent. [14]
231	Code	A method of information representation by mapping it into a machine-readable alphabet, e.g. Textual information may be represented in computer memory by the ascii or the ebcdic alphabet. [14]
232	Dock	The space between two piers. Also called a slip. [14]
233	List	Inclination to one side, as of a vessel until she has found equilibrium in an inclined position. Listing is a static condition, as distinguished from heeling which is dynamic. See heel. [14]
234	Chain	A group of transmitters broadcasting the same programme. In electronic navigation, several related transmitting stations in geographic proximity (decca chain, loran chain, etc.). In digital data, a sequence of one or more-line segments. [14]
235	Crust	In geology, the outer layer of the solid earth; the lithosphere. Also called earth's crust. [14]
236	Drift	(v.i.). To move by action of wind or current without control. [14]
237	Drift	The speed of the water due to ocean or tidal currents. A wide, slow-moving current principally caused by winds. The distance a craft is moved by current and wind. Drift angle or leeway. The term is also applied to any superficial deposit caused by a current of water or air. [14]
238	Strip	In ice terminology, a long narrow area of pack ice, about 1 km or less in width, usually composed of small fragments detached from the main mass of ice, and run together under the influence of wind, swell or current. [14]
239	Border	The district lying along the edge of a country or territory; a frontier. The boundary line which separates one country from another, the frontier line. [14]
240	Counter	An indicator on a machine, for keeping count of turns, strokes, etc., of the machine or its parts. [14]
241	Eclipse	The obscuration of a source of light by the intervention of an object. Whole or partial obscuration of a heavenly body by the interposition of another, or by the passing of one luminous heavenly body into the shadow of another. [14]
242	Equinox	One of the two points of intersection of the ecliptic and the celestial equator, occupied by the sun when its declination is zero. That point occupied on or about March 21, when the sun's declination changes from south to north, is called vernal equinox or first point of aries; that point occupied on or about September 23, when the declination changes from north to south, is called autumnal equinox or first point of libra. Also called equinoctial point. [14]
243	Receiver	One who or that which receives anything, particularly a radio receiver. [14]
244	Continent	One of the main continuous bodies of land on the earth's surface. The mainland, as distinguished from outlying islands, mainland. [14]
245	Reduction	The process of substituting for an observed value one derived therefrom. [14]
246	Thunderstorm	One or more sudden electrical discharges manifested by the flash of light (lightning) and a sharp or rumbling sound (thunder). [14]
247	Gal	(derived from galileo). The unit of acceleration in the cgs system. See milligal. [14]
248	Pip	See blip. [14]
249	Pile	a long heavy timber or section of steel, wood, concrete, etc., forced into the earth or sea floor to serve as a support, as for a pier, or to resist lateral pressure, or as a free standing pole within a marine environment. [14]
250	Till	Unstratified glacial drift consisting of clay, sand, gravel, and boulders intermingled in any proportions. Also called boulder clay. [14]
251	Beach	On a shore, the area on which the waves break and over which shore debris, such as sand, shingle, pebbles accumulate. A beach includes backshore and foreshore. [14]
252	Gauge	An instrument for measuring the size or state of anything. [14]
253	Needle	Short for magnetic needle. [14]
254	Seabed	See sea floor. [14]
255	Symbol	A character, letter, or similar graphic representation used on a chart, map, hydrographic survey sheet, or diagram to represent some object, quantity, characteristic, etc. [14]
256	Analysis	The drawing and interpretation of the patterns of various weather elements on a surface or upper-air chart. [1]
257	Exposure	In photography, the act of exposing a light-sensitive material to a light source. The total quantity of light received per unit area on a sensitized plate or film; may be expressed as the product of the light intensity and the exposure time. [14]
258	Salinity	A measure of the quantity of dissolved salts in sea water. It is normally defined as the total amount of dissolved solids in sea water in parts per thousand ( °) by weight when all the carbonate has been converted to oxide, the bromide and iodide to chloride, and all organic matter is completely oxidiz-ed. These qualifications result from the chemical difficulty in drying the salts in sea water. In practice, salinity is not determined directly but is computed from chlorinity, electrical conductivity, refractive index, or some other property whose relationship to salinity is well established. Because of the law of constancy of proportions, the amount of chlorinity in a sea water sample is used to establish the sample's salinity. The relationship between chlorinity cl and salinity s as set forth in Knudsen’s tables is s = 0.03 + 1.805 cl. A joint committee of IAPO, UNESCO, ICES, and SCOR proposed the universal adoption of the following equation for determining salinity from chlorinity: s = 1.80655 cl. It was adopted by IAPO in 1963 and ices in 1964. [14]
259	Spectrum	(pl. Spectra). A series of images formed when a beam of radiant energy is separated into its various wavelength components, as when a beam of white light is refracted and dispersed by a prism. The entire range of electromagnetic radiations, or any part of it used for a specific purpose, as the radio spectrum (10 kilohertz to 300,000 megahertz). [14]
260	Precision	The degree of refinement of a value not to be confused with accuracy, which is the degree of conformance with the correct value. [14]
261	Conjunction	In astronomy, the situation of two celestial bodies having the same celestial longitude or the same sidereal hour angle. For a superior planet, it occurs when the sun is between the earth and the planet. [14]
262	Frequency: Radio	Any frequency at which electromagnetic radiation of energy is useful for communication. Radio frequencies are usually classed as very low, below 30 kilohertz; low, 30-300 kilohertz; medium, 300-3,000 kilohertz; high, 3-30 megahertz; very high, 30-300 megahertz; ultra-high, 300-3,000 megahertz; super high, 3,000-30,000 megahertz; extremely high, 30,000-300,000 megahertz. [14]
263	Mud	Pelagic or terrigenous detrital material consisting mostly of silt and clay-sized particles (less than 0.06 millimeter) but often containing varying amount of sand and/or organic materials. It is a general term applied to any sticky fine-grained sediment whose exact size classification has not been determined. [14]
264	Stop	See aperture stop. [14]
265	Geoid	The figure of the earth considered as a mean sea level surface extended continuously through the continents. The actual geoid is an equipotential surface to which, at every point, the plumb line (direction in which gravity acts) is perpendicular. It is the geoid which is obtained from observed deflections of the vertical and is the surface of reference for astronomical observations and for geodetic levelling. See reference spheroid. [14]
266	Wreck	The ruined remains of a stranded or sunken vessel which has been rendered useless. See also dangerous wreck, and derelict. [14]
267	Radial	A straight line extending outward from a center. In photogrammetry, a line or direction from the radial center to any point on a photograph. The radial center is assumed to be the principal point, unless otherwise designated (e.g., nadir radial). See also isoradial. [14]
268	Overlap	In cartography and surveying, the amount by which one chart or survey sheet extends also over an adjoining chart or sheet. The amount by which different sets of survey data, obtained with the same system, cover the same area; customarily expressed as a percentage. [14]
269	Sea Ice	Any form of ice which has originated from sea water. Generally, any ice in the sea. [14]
270	Amplitude	In astronomy, the arc of the horizon, between a celestial body at rising or setting and true east or west point. In tide terminology, the semi-range of the harmonic constituent. In physics, the maximum departure of a wave or other periodic phenomenon from the average or zero position. [14]
271	Distortion	An undesired change in waveform. In optics, an aberration affecting the position of the images off the axis, in which objects at different angular distances from the axis undergo different magnifications. Also called lens distortion. In photography, any shift in the position of an image on a photograph which alters the perspective characteristics of the photograph. Causes of image distortion include lens aberration, differential shrinkage of film or paper, and motion of the film or camera. [14]
272	Inequality	A systematic departure from the mean value of a quantity. See annual inequality, diurnal inequality, lunar inequality, parallax inequality, phase inequality. [14]
273	Reflection	The process whereby a surface of discontinuity turns back a portion of the incident radiation into the medium through which the radiation approached. See surface reflection. [14]
274	Sea Bottom	See sea floor. [14]
275	Declination	In astronomy, the angle at the center of the celestial sphere between the radius passing through a celestial body and the plane of the celestial equator. Declination is measured by the arc of the hour circle between the celestial body and the celestial equator. It is plus when the body is north of the equator, and minus when south of it. [14]
276	Obstruction	In marine navigation, anything that hinders or prevents movement, particularly anything that endangers or prevents passage of a vessel. The term is usually used to refer to an isolated danger to navigation, such as a sunken rock or pinnacle. [14]
277	Precipitation	Phenomenon made up of an aggregate of aqueous particles, liquid or solid, crystallized, or amorphous, which fall from a cloud or group of clouds and reach the ground. [14]
278	Lee	That side towards which the wind blows; the sheltered side. [14]
279	Race	Swiftly flowing water in a narrow channel or river; also, the channel itself which may be artificial as in a mill-race. Also, a swift rush of water through a narrow channel in tidal waters and caused by the tidal movement of the waters. See tide race. [14]
280	Scan	See scope. [14]
281	Stone	A general term for rock and rock fragments ranging in size from pebbles and gravel to boulders or large rock masses. [14]
282	Watch	A small timepiece of a size convenient to be carried on the person. [14]
283	Mirror	Any surface which produces images by reflection of light rays. [14]
284	Target	Any object, point, etc., toward which something is directed. An object which reflects a sufficient amount of a radiated signal to produce an echo signal on detection equipment. See radar target, sonar target. The distinctive marking or instrumentation of a ground point to aid in its identification on a photograph. In photogrammetry, target designates a material marking so arranged and placed on the ground as to form a distinctive pattern over a geodetic or other control point marker, on a property corner or line, or at the position of an identifying point above an underground facility or feature. A target is also the image pattern on aerial photographs of the actual mark placed on the ground prior to photography. [14]
285	Diagram	A graphic representation of certain data. [14]
286	Humidity	Atmospheric water vapour content, expressed in any of several measures, such as relative humidity. [14]
287	Barometer	Instrument for measuring atmospheric pressure. [14]
288	Submerged	(Adj.). Under water; not showing above water. The opposite is uncovered. [14]
289	Tidal Day	Lunar day. The period of the daily cycle of the tides, differing slightly from the lunar day because of priming and lagging of the tide. [14]
290	Adjustment	The determination and application of corrections to observations or measurements, for the purpose of reducing errors or removing internal inconsistencies in observed results. Adjustment may either refer to mathematical procedures or to corrections applied to instruments. [14]
291	Visibility	The extreme horizontal distance at which prominent objects can be seen and identified by the unaided eye. [14]
292	Bore	A high breaking wave of water, advancing rapidly up an estuary. Bores can occur at the mouths of shallow rivers if the tide range at the mouth is large. They can also be generated in a river when tsunamis enter shallow coastal water and propagate up the river. Also called eager, mascaret, or tidal bore. [14]
293	Basin	a depression of the sea floor more or less equidimensional in plan and of variable extent. [14]
294	Plain	Any land with a flat or very slightly undulating surface. A flat, gently sloping or nearly level region of the sea floor, for example, abyssal plain. [14]
295	Platform	In geographical literature, a natural or artificial terrace; a flat elevated piece of ground; a tableland, a plateau. In oceanographic terminology, any man-made structure (aircraft, ship, buoy, or tower) from or on which oceanographic instruments are suspended or installed. Structures which are erected on or over the seabed and subsoil for the purpose of exploring for, developing, removing and transporting resources therefrom. [14]
296	Parameter	A quantity which remains constant within the limits of a given case or situation. [14]
297	Reckoning	In navigation, computation by which the position of a ship is found. See dead reckoning. [14]
298	Protractor	An instrument for measuring angles on a surface; an angular scale. In its most usual form, it consists of a circle or part of one (usually a semicircle) graduated in degrees. See protractor: three arm and compass rose. [14]
299	Aerial Photograph	See photography. [14]
300	Sue	The vertical amount which a vessel aground dries due to the fall of the tide. [14]
301	Dust	Any substance comminuted or pulverized, especially earth or other solid matter in a minute and fine state of subdivision, so that the particles are small and light enough to be easily raised and carried in a cloud by the wind. [14]
302	Inch	A unit of length equal to 1/12 of a foot or 2.54 cm. [14]
303	Noon	The instant at which a time reference is over the upper branch of the reference meridian. [14]
304	Soil	The earth or ground; the face or surface of the earth. The ground with respect to its composition, quality, etc., or as the source of vegetation. [14]
305	Scree	A mass of detritus, forming a precipitous, strong slope upon a mountainside. Also, the material composing such a slope. See also talus. [14]
306	Fixing	The process of rendering a developed photographic image permanent by removing the unaffected light-sensitive material. [14]
307	Margin	In cartography, that area of a map or chart lying outside the border. 'Margin' is preferred to the term 'surround'. [14]
308	Screen	A device to shield or separate one part of an apparatus from other parts, or to separate the effects of one part on others. In electronic charting, a device connected to a computer displaying information either under computer control, or under user control, e.g. On a cathode-ray tube. Devices allowing for high resolution are capable of displaying also graphics. [14]
309	Digital	A method of representing information by combinations of discrete and discontinuous data. [14]
310	Lightning	Luminous manifestations accompanying a sudden electrical discharge which takes place from or inside a cloud or, less often, from high structures on the ground or from mountains. [14]
311	Navigable	(Adj.). Affording passage to a craft; capable of being navigated. [14]
312	Depression	Any hollow or relatively sunken area. In meteorology, a region of the atmosphere in which the pressure is low relative to the surrounding region at the same level. It is represented on a weather chart by a system of isobars at a specified level or of contours at a specified pressure which enclose relatively low values of pressure or level. Also, called low or cyclone. [14]
313	Focal Plane	A plane parallel to the plane of a lens or mirror and passing through the focus. In photography, the plane (perpendicular to the axis of the lens) in which images of points in the object field of the lens are focused. [14]
314	Water Vapor	Water in the gaseous phase. [14]
315	Lunitidal Interval	The interval of time between the transit (upper or lower) of the moon over the local or Greenwich meridian and the next high water or low water at a place. The interval is assumed to be local unless otherwise specified. The average of all high-water intervals is called mean high water lunitidal interval, high water interval, or corrected establishment. The average of all low water intervals is called mean low water lunitidal interval, or low water interval. The expressions higher high-water interval, lower high water interval, higher low water interval, and lower low water interval are used when there is considerable diurnal inequality. See establishment. [14]
316	Lux	Unit of illumination in the si system. [14]
317	Berg	Short for iceberg. [14]
318	Cone	See fan. [14]
319	Knot	A division of the log line, by which the ship's speed is measured. A nautical unit of speed. One knot is one nautical mile per hour. The name is derived from the knots in the log line. [14]
320	Focus	(pl. Foci). That point at which parallel rays of light meet after being refracted by a lens or reflected by a mirror. Also called focal point. In seismology, the source of a given set of elastic waves. The true center of an earthquake, within which the strain energy is first converted to elastic wave energy. [14]
321	Focus	(v.t.). The process of adjusting an optical instrument, projector, cathode-ray tube, etc., to produce a clear and well-defined image. [14]
322	Globe	The earth; the world. A spherical structure on whose surface is depicted the geographical configuration of the earth (terrestrial globe). [14]
323	Pivot	A spindle or pin by which a movable part of an instrument is supported so as to be free to turn. The pivot of a compass is usually a fixed point on which the needle hangs by a single jeweled cap. [14]
324	Rhumb	See rhumb line. [14]
325	Sonar	A system of determining distance of an underwater object by measuring the interval of time between transmission of an underwater sonic or ultrasonic signal and the return of its echo. Direction may also be determined by noting the direction of transmission of the signal. The name sonar is derived from the words sound navigation and ranging. See echo ranging. [14]
326	Alidade	Pivoted sight bar that moves over a graduated arc. The upper part of a theodolite. The alidade used in topographic surveying consists of a straight-edge ruler carrying a telescope or other sighting device and used in recording a direction on the plane table sheet. The term is also used to describe a bearing circle fitted with a telescope to facilitate observation of bearings. If a telescope is used, the instrument is often termed a telescopic alidade. [14]
327	Display	A visual presentation of data. [14]
328	Air Mass	Ensemble of air particles whose paths and physical properties exhibit, in the horizontal, only small, and continuous differences. The mass may extend over an area of several million square miles and over a depth of several kilometers. [14]
329	Ecliptic	The great circle formed by the intersection of the plane of the earth's orbit around the sun (or apparent orbit of the sun around the earth) and the celestial sphere. [14]
330	Diurnal Inequality	The difference between the heights of the two high tides (high water inequality) or the two low tides (low water inequality) during a tidal day, or the difference in speed between the two flood or the two ebb currents during a tidal day. The average diurnal inequality is called tropic high-water inequality and tropic low water inequality when referred to the high waters and low waters, respectively, of tropic tides. Mean diurnal high-water inequality is half the average difference between the heights of the two high waters of each tidal day over a 19-year period. Mean diurnal low water inequality is half the average difference between the heights of the two low waters for a similar period. Also called declinational inequality. [14]
331	Node	A point that is the start or end point of a line segment. In astronomy, one of the two points of intersection of the orbit of a planet, planetoid, or comet with the ecliptic, or of the orbit of a satellite with the plane of the orbit of its primary. That point at which the body crosses to the north side of the reference plane are called the ascending node; the other, the descending node. The line connecting the nodes is called line of nodes. Also called nodal point. See regression of the nodes. In oceanography, that part of a standing wave where the vertical motion is least, and the horizontal velocities are greatest. See partial node. In optics, a nodal point. [14]
332	Pipe	A hollow metal tube, of varying diameters and lengths, imbedded in the bottom in a manner similar to a pile. Pipes are often used as privately maintained aids to navigation and in the determination of beach or bottom sand migration (deposition or erosion). [14]
333	Wash	The visible or audible motion of agitated water; especially that caused by the passage of a vessel. [14]
334	Otter	Plane surface towed forward of its middle length so that it will incline and dive. Used in fishing, minesweeping or surveying. See kite, kite otter, and Oropesa sweep. [14]
335	Scend	Upward motion of a vessel, either upward motion of the bow and stern associated with pitching or lifting of the entire vessel by waves or swell, when it may be called send. [14]
336	Arming	Tallow or other substance placed in the recess at the lower end of a sounding lead for obtaining a sample of the bottom. See bottom sample. [14]
337	Moment	The tendency or degree of tendency to produce motion about an axis. Numerically it is the quantity obtained by multiplying the force, speed, or mass, by the distance from the point of application or center of gravity to the axis. See magnetic moment. [14]
338	Mosaic	In photogrammetry, as assembly of aerial photographs whose edges usually have been torn, or cut, and matched to form a continuous photographic representation of a portion of the earth's surface. [14]
339	Carrier	See wave: carrier. [14]
340	Mooring	A place where a vessel may be secured. (usually in pl.) The equipment used to secure a vessel. The process of securing a vessel or oceanographic instruments other than anchoring with a single anchor. [14]
341	Network	In surveying, a pattern or configuration of stations called geodetic network. In geography, a complex system of rivers, canals, etc. In radio, a chain of transmitting radio stations owned and operated as a unit. [14]
342	Air Base	In photogrammetry, the line joining two air stations, or the length of this line; also, the distance (at the scale of the stereoscopic model) between adjacent perspective centers as reconstructed in the plotting instrument. See also photo base. [14]
343	Low Tide	See low water. [14]
344	Hurricane	Term, derived from a Caribbean word, first applied to tropical cyclones of the Caribbean sea. Wind with a speed equal to or greater than 58 knots. (Beaufort scale wind force 12.) [14]
345	Transport	The process by which a substance or quantity is carried past a fixed point, or across a fixed plane. In oceanography and meteorology, such quantities are: heat, momentum, mass, dissolved impurities, suspended particles, etc. [14]
346	Hour Angle	Angular distance west of a celestial meridian, the arc of the celestial equator, or the angle at the celestial pole, between the upper branch of a celestial meridian and the hour circle of a celestial body or the vernal equinox, measured westward through 24 hours (360o). It is usually further designated as local, Greenwich, or sidereal, as the origin of measurement is the local or Greenwich meridian, or the hour circle of the vernal equinox. [14]
347	Modulation	Variation of some characteristic of a wave, called the carrier wave, in accordance with instantaneous values of another wave, called the modulating wave. Variation of amplitude is amplitude modulation, variation of frequency is frequency modulation, and variation of phase is phase modulation. See modulation: pulse and modulation: space. [14]
348	Phenomenon	(pl. Phenomena). Any fact, circumstance, or experience that is apparent to the senses and that can be scientifically described or appraised; as, an eclipse is a phenomenon of astronomy. [14]
349	Sound Wave	See wave. [14]
350	Earth'S Magnetic Field	See geomagnetic field. [14]
351	Limb	The graduated curved part of an instrument for measuring angles, as that part of a marine sextant carrying the altitude scale, or arc. The circular outer edge of a celestial body. The half with the greatest altitude is called the upper limb and the half with the least altitude, the lower limb. [14]
352	Mole	A massive structure of masonry or large stones serving as a pier or breakwater, or both. Unit of quantity of matter in the si system. [14]
353	Cliff	Land rising abruptly for a considerable distance above the water or surrounding land. [14]
354	Coral	Hard calcareous skeletons of many tribes of marine polyps. [14]
355	Corer	A device for obtaining a core; a hollow tube that is driven into the ocean floor. Also called coring instrument or coring device. See corer: hydro plastic, corer: piston, piggot gun and vacuum lead. [14]
356	Input	What is put in, as electric current or other power put into a machine. Data to be transferred from an external storage medium, such as punched cards, into the internal storage of a computer. [14]
357	Shade	A coloured glass that can be moved into the line of sight of an optical instrument, such as a sextant, to reduce the intensity of light reaching the eye. Also, calledshade glass. See horizon shade, and index shade. [14]
358	Swell	Ocean waves which have travelled out of their generating area. Swell characteristically exhibits a more regular and longer period and has flatter crests than waves within their fetch. Rising of the water of a river above its usual level. Gently rising ground or a rounded hill above the surrounding ground. [14]
359	Fathom	A unit of length equal to 6 feet or 1.83 meters. [14]
360	Marker	That which marks something. A marker beacons. See also radio beacon. [14]
361	Master	An instrument which controls another similar instrument called a repeater. A master station. [14]
362	Output	The amount of power or energy produced by a machine. [14]
363	Trough	A long depression of the sea floor characteristically flat bottomed and steep sided and normally shallower than a trench. [14]
364	Valley	A long depression or hollow in the land lying between hills or stretches of high ground and usually having a river or stream flowing along the bottom. [14]
365	Buoyage	A system of, or providing with, buoys, serving the purpose of indicating navigable waters. See beaconage. [14]
366	Thermal	A small, rising parcel of warm air produced when the earth's surface is heated unevenly. [1]
367	Freezing	See frost. [14]
368	Sidereal	(Adj.). Of or pertaining to the stars. [14]
369	Solstice	One of the two points of the ecliptic farthest from the celestial equator; one of the two points on the celestial sphere occupied by the sun at maximum north or south declination. That in the northern hemisphere is called the summer solstice or first point of cancer, and that in the southern hemisphere, the winter solstice or first point of Capricorn. Also called solstitial point. That instant at which the sun reaches one of the solstices, about June 21 (summer solstice) or December 22 (winter solstice). [14]
370	Altimeter	An instrument that directly indicates the height above a reference surface. [14]
371	Anchorage	An area in which vessels anchor or may anchor. [14]
372	High Tide	See high water. [14]
373	Magnetize	(v.t.). To produce magnetic properties. The opposite is demagnetized. [14]
374	Magnitude	The importance, quality, or size of something. In astronomy, relative brightness of a celestial body. According to the accepted classification, a star of the 1st magnitude is a hundred times as bright as a star of the 6th magnitude (the faintest star that can be seen with the unaided eye) and the dis-tribution of magnitudes is logarithmic in terms of brightness. Thus, each reduction in magnitude means an increase of brightness of about 2 1/2. [14]
375	Mountains	On the sea floor, a well-delineated subdivision of a large and complex positive feature. See cordillera. [14]
376	Solar Day	See day. [14]
377	Wind Speed	Ratio of the distance covered by the air to the time taken to cover it. The 'instantaneous speed' or, more briefly, the 'speed', corresponds to the case of an infinitely small-time interval. The 'mean speed' corresponds to the case of a finite time interval. [14]
378	Compilation	in cartography, the selection, assembly, and graphic presentation of all relevant information required for the preparation of a map or chart, or a new edition or part thereof. Such information may be derived from other maps or charts, aerial photographs, surveys, new data, and other sources. In photogrammetry, the production of a map (or portion of a map) from aerial photographs and geodetic control data, by means of photogrammetric instruments. Sometimes called stereo compilation. [14]
379	Hour Circle	A great circle on the celestial sphere passing through the celestial poles. Also called declination circle, circle of declination, or circle of right ascension. [14]
380	Probability	The likelihood of an event measured by the ratio of the favorable cases to the whole number of cases possible. [14]
381	Mean Sea Level	The average height of the surface of the sea at a tide station for all stages of the tide over a 19-year period, usually determined from hourly height readings measured from a fixed predetermined reference level (chart datum). [14]
382	Atom	The smallest particle of an element which can enter into a chemical combination. [14]
383	Drag	(v.t.). To tow a line or object below the surface to determine the least depth in an area or to ensure that a given area is free from navigational dangers to a certain depth. See also sweep. To pull along the bottom, as an anchor. [14]
384	File	An entity of data for a specific task or purpose stored on a mass storage device. [14]
385	Horn	Fog signal using compressed air or electricity to vibrate a diaphragm. Horns exist in a variety of types which differ greatly in their sound and power. Further to the recent action taken by the hydrogra-pher of the United Kingdom. Such terms as nautophone, typhon and others are gradually being embraced by the general term 'horn'. [14]
386	Pull	An impression from an individual printing plate. [14]
387	Rips	A turbulent agitation of water generally caused by the interaction of currents and wind; in nearshore regions, rips may also be caused by currents flowing swiftly over an irregular bottom. [14]
388	Grade	Rate of slope or degree of inclination, as a 2% grade. See also gradient and grad. [14]
389	Heave	The oscillatory rise and fall of a ship due to the entire hull being lifted by the force of the sea. [14]
390	Hertz	A unit of frequency in the si system. See also cycle per second. [14]
391	Patch	In ice terminology, a collection of pack ice, less than 10 km across. [14]
392	Surge	A ship's bodily motion forward and backward along the longitudinal axis, caused by the force of the sea acting alternately on the bow and stern. The name applied to wave motion with a period intermediate between that of the ordinary wind wave and that of the tide, from about 1/2 to 60 minutes. Horizontal oscillation of water with comparative short period accompanying a seiche. [14]
393	Surge	(v.i.). To rise and fall, as a vessel at anchor. To vary abruptly and momentarily in amount, as an electric current in a circuit. [14]
394	Ashore	(Adj. And adv.). On the shore, on land or aground. [14]
395	Breeze	A wind of moderate strength. See land and sea (or lake) breeze. [14]
396	Stadia	A graduated rod used in the determination of distance by observing the intercept on the rod subtending a small known angle at the point of observation. In practice the angle is usually defined by two fixed lines in the reticle of a telescope. Also called stadia rod. [14]
397	Geodesy	The science which treats of the determination of the size and figure of the earth (geoid) by such direct measurements as triangulation, levelling and gravimetric observations. [14]
398	Glacier	A mass of snow and ice continuously moving from higher to lower ground or, if afloat, continuously spreading. The principal forms of glaciers are: ice sheets, ice shelves, ice caps, ice piedmonts, and various types of mountain glaciers. [14]
399	Lattice	A pattern formed by two or more families of intersecting lines, such as hyperbolic lines of position or parts of circles, drawn on charts, plotting sheets or sounding boards. [14]
400	Sinking	A downward movement of surface water generally caused by converging currents or when water mass becomes denser than the surrounding water. See upwelling, and convergence. An apparent lowering of distant terrestrial objects by abnormal atmospheric refraction. Because of sinking, objects normally visible at or near the horizon sometimes disappear below the horizon. The opposite is looming. [14]
401	Spatial	(Adj.). Pertaining to or limited by space. [14]
402	Response	For a device or system, the motion or other output resulting from an excitation or stimulus under special conditions. [14]
403	Routeing	A complex of measures concerning routes followed by ships and aiming at reducing the risk of casualties (traffic separation schemes, deep-draught routes, areas to be avoided, etc.). [14]
404	Twilight	The periods of incomplete darkness following sunset (evening twilight) or preceding sunrise (morning twilight). Twilight is designated as civil, nautical, or astronomical, as the darker limit occurs when the center of the sun is 6°, 12°, or 18° below the celestial horizon, respectively. [14]
405	Base Line	The line from which the outer limits of the territorial sea and certain other outer limits are measured. In radiolocation, the geodesic line between two stations operating in conjunction for the determination of a line of position. Also written as one word. See also base. [14]
406	Calibrate	V.t.). To fix, check or correct the graduations of a measuring instrument. To determine the calibre of. [14]
407	Coastline	The line where shore and water meet. Shoreline and coastline are generally used synonymously. [14]
408	Gyroscope	A rapidly rotating mass free to move about one or both axes perpendicular to the axis of rotation and to each other. It is characterized by gyroscopic inertia and precession. Sometimes shortened to gyro. [14]
409	Objective	See objective lens. [14]
410	Starboard	The right side of a craft facing forward. The opposite is port. [14]
411	Fog Signal	A warning signal transmitted by a vessel or aid to navigation during period of low visibility. Also, the device producing such a signal. [14]
412	Precession	Change in the direction of the axis of rotation of a spinning body, as a gyroscope, when acted upon by a torque. The direction of motion of the axis is such that it causes the direction of spin of the gyroscope to tend to coincide with that of the impressed torque. [14]
413	Topography	The configuration of the surface of the earth, including its relief, the position of its streams, roads, cities, etc. The earth's natural and physical features collectively. In oceanography, the term is applied to a surface such as the sea bottom or a surface of given characteristics within the water mass. [14]
414	Transducer	Any device for converting energy from one form to another (electrical, mechanical, or acoustic). [14]
415	Equilibrium	A state of balance between forces. [14]
416	Photography	The art or process of producing images on sensitized material through the action of light. [14]
417	Plane Table	A field device for plotting the lines of a survey directly from the observations. It consists essentially of a drawing board mounted on a tripod, with a ruler on which a telescope or other sighting device is mounted. See alidade. Also written as one word. [14]
418	Atmospheric Pressure	See pressure. [14]
419	Fan	A relatively smooth, fan-like depositional feature normally sloping away from the outer termination of a canyon or canyon system. Also called cone. [14]
420	Clay	Mineralogically, a hydrous aluminium silicate material with plastic properties and a crystal structure. As a size term, refers to sediment particles ranging from 0.0039 to 0.00024 millimeter, in which case it includes rock flour, calcareous muds, aragonite, etc. [14]
421	Gust	A sudden brief increase in the speed of the wind. [14]
422	Heel	Transverse inclination of a vessel due to the action of waves, wind, a greater weight on one side, etc. See also list. [14]
423	Mist	Suspension in the air of microscopic water droplets or wet hygroscopic particles, reducing the visi-bility at the earth's surface. [14]
424	Pier	A long, narrow structure extending into the water to afford a berthing place for vessels, to serve as a promenade, etc. See also jetty. [14]
425	Send	See scend. [14]
426	Vane	A device to indicate the direction from which the wind blows. Also called weathervane, wind vane. See anemometer. A sight on an instrument used for observing bearings, as on a pelorus, bearing circle, etc. Also called sight (or sighting) vane. A device to indicate the direction toward which the current flows. [14]
427	Ahead	Bearing approximately 000° relative. The term is often used loosely for dead ahead or bearing exactly 000° relative. The opposite is astern. [14]
428	Berth	Place in which a ship is moored at wharf. [14]
429	Epoch	A given period of time during which a series of related acts or events takes place. In astronomy, a particular instant for which certain data are given or at which an observation is made, and which then is usable as a reference point. [14]
430	Pilot	1. A person who directs the movements of a vessel through pilot waters, usually a person who has demonstrated extensive knowledge of channels, aids to navigation, dangers to navigation, etc., in a particular area and is licensed for that area. 2. A book of sailing directions. [14]
431	Sweep	(v.t. & i.). To tow a line or object below the surface, to determine the least depth in an area or to ensure that a given area is free from navigational dangers to a certain depth; or the removal of such dangers. [14]
432	Swing	In photogrammetry, a rotation of a photograph in its own plane about its camera axis. [14]
433	Wharf	A structure serving as a berthing place for vessels. [14]
434	Afloat	Floating, as opposed to being aground. [14]
435	Astern	Bearing approximately 180° relative. The term is often used loosely for dead astern or bearing exactly 180° relative. The opposite is ahead. [14]
436	Bridge	1. An elevated structure extending across or over the weather deck of a vessel, or part of such a structure. The term is sometimes modified to indicate the intended use, such as navigating bridge or signal bridge. 2. A structure erected over a depression or an obstacle such as a body of water, railroad, etc., to provide a roadway for vehicles or pedestrians. [14]
437	Dredge	(v.t.). To remove solid matter from the bottom of a water area. [14]
438	Dredge	An apparatus for bringing up solid material from the bottom of a water area, gathering deep water organisms, etc. A dredger. [14]
439	Anomaly	Deviation from the normal or natural characteristics of a phenomenon. Abnormality. In astronomy, true anomaly is the angle at the sun between lines connecting the sun with a planet and with the planet's perihelion. Mean anomaly and eccentric anomaly are also considered. [14]
440	Breaker	A wave breaking on the shore, over a reef, etc. Breakers may be roughly classified into three kinds, although the categories may overlap: spilling breakers break gradually over a considerable distance; plunging breakers tend to curl over and break with a crash; and surging breakers peak up, but then instead of spilling or plunging they surge up on the beach face. The french word 'brisant' is also used for the obstacle causing the breaking of the wave. [14]
441	Ellipse	A plane curve constituting the locus of all points the sum of whose distances from two fixed points, called foci, is constant. Also used to characterize errors in positions and measurements. [14]
442	Leeward	(Adj. And adv.). Toward the lee, or in the general direction toward which the wind is blowing. The opposite is windward. [14]
443	Release	A device for holding or releasing a mechanism, particularly the device by which the tangent screw of a sextant or surveying instrument is held in place or disengaged from the limb, or circle respectively. In oceanography acoustic releases are used to sever deployed instruments from their anchoring. [14]
444	Shutter	In photography, the mechanism of a camera which controls the length of time the emulsion is exposed. [14]
445	Infrared	(Adj.). Having a frequency immediately beyond the red end of the visible spectrum said of rays of longer wavelength than visible light, but shorter than radio waves. [14]
446	Pack Ice	Term used in a wide sense to include any area of sea ice, other than fast ice, no matter what form it takes or how it is disposed. Pack ice may be described as very open pack ice (1/10ths-3/10ths), open pack ice (4/10ths-6/10ths), close pack ice (7/10ths-9/10ths), very close pack ice (almost 10/10th with little if any water visible). [14]
447	Quadrant	A double-reflecting instrument for measuring angles. It is similar to a sextant, but has an arc of 90°. Also a surveying or astronomical instrument composed of a graduated arc about 90° in length, equipped with a sighting device. [14]
448	Terminal	A number of berths grouped together, providing facilities for handling a particular form of cargo, e.g. Oil terminal, container terminal. [14]
449	Windward	(Adj. And adv.). In the general direction from which the wind blows; in the wind; on the weather side. The opposite is leeward. [14]
450	Broadcast	Communication by radio intended for reception at any point within a specified area. [14]
451	Departure	The distance between two meridians at any given parallel of latitude expressed in linear units, usually nautical miles. The distance to the east or west made good by a vessel in proceeding from one point to another. [14]
452	Diaphragm	In a telescope, a thin glass disk on which etched lines forming a reticle are placed. See also reticle, and aperture stop. [14]
453	Light Ray	The geometrical concept of a single element of light propagated in a straight line and of infinitesimal cross-section; used in analytically tracing the path of light through an optical system. [14]
454	Stability	Property of the state of rest or continuous movement of a system such that any disturbance intro-duced into this state decreases. In meteorology, the term is often used as a synonym of static stability. [14]
455	Convection	In general, mass motions within a fluid resulting in transport and mixing of the properties of that fluid. In the atmosphere, organized internal motions within a layer of air, leading to vertical transport of heat, momentum, etc. [14]
456	Oscillator	A device for producing oscillations, especially one of the non-rotating type, as the sound generator of a sonic depth finder or a radio frequency generator. A submarine oscillator is a large, electrically-operated diaphragm horn which produces a sound for transmission through water. [14]
457	Rhumb Line	A line on the surface of the earth making the same oblique angle with all meridians; a loxodrome spiraling toward the poles in a constant true direction. Parallels and meridians, which also maintain constant true directions, may be considered special cases of the rhumb line. A rhumb line is a straight line on a Mercator projection. Sometimes shortened to rhumb. [14]
458	Solar Time	See time. [14]
459	Cartography	The art and science of expressing graphically, by maps and charts, the known physical features of the earth, or of another celestial body. Often includes the works of man and his varied activities. [14]
460	Chart Datum	See datum: chart. [14]
461	Chronometer	A portable timekeeper with a compensated balance, capable of showing time with extreme precision and accuracy. [14]
462	Depth Curve	A depth curve is a line connecting points of equal water depth which is sometimes significantly displaced outside of soundings, symbols, and other chart detail for clarity as well as generalization. Depth curves therefore often represent an approximate location of the line of equal depth as related to the surveyed line delineated on the source. [14]
463	Wave Height	The vertical distance between a crest and the preceding trough. [9]
464	Celestial Equator	See equator. [14]
465	MHW	Mean High Water (MHW) ; The average of all the high water heights observed. [21]
466	MLW	Mean Low Water (MLW) ; The average of all the low water heights observed. [21]
467	Belt	In ice terminology, a long area of pack ice from a few kilometers to more than 100 kilometers in width. [14]
468	Rime	A white or milky granular deposit of ice formed by the rapid freezing of supercooled water drops as they come in contact with an object in below-freezing air. [1]
469	Smog	Originally smog meant a mixture of smoke and fog. Today, smog means air that has restricted visibility due to pollution, or pollution formed in the presence of sunlight/photochemical smog. [1]
470	Marsh	A tract of low-lying land flooded at times and generally swampy. [14]
471	Pitch	The oscillations of a ship about the transverse axis, due to the bow and stern being raised or lowered on passing through successive crests and troughs of waves. Also called pitching. The distance along the axis of a screw or other helix between consecutive threads or ribs. The distance a propeller would advance longitudinally, in one revolution if there were no slip. [14]
472	Pound	A unit of mass, equal to 0.45359237 kilograms. [14]
473	Gnomon	Any object the shadow of which serves as an indicator, as the shadow pin of a sun compass. [14]
474	Pencil	In optics, a set of rays coming to or spreading out from a point. See light pencil. [14]
475	Strait	(also straits). A passage connecting two larger bodies of water. [14]
476	X-Rays	Electromagnetic radiation of the same nature as visible radiation but of an extremely short wavelength less than 10-2 micrometers. X-rays are used in radar technology. [14]
477	Drizzle	Fairly uniform precipitation composed exclusively of fine drops of water (diameter less than 0.5 mm), very close to one another. [14]
478	Drizzle	Small water drops between 0.2 and 0.5 mm in diameter that fall slowly and reduce visibility more than light rain. [1]
479	Hummock	A natural elevation of the earth's surface resembling a hillock, but smaller and lower. In ice terminology, a mound of ice raised by pressure. May be fresh or weathered. [14]
480	Opening	A break in a coastline or a passage through a reef, between shoals, etc. Any break in sea ice which reveals the water. [14]
481	Perigee	That orbital point nearest the earth when the earth is the center of attraction, as opposed to apogee. [14]
482	Plotter	An instrument used for plotting straight lines and measuring angles on a chart or plotting sheet. See protractor. In data processing it stands for (a) vector plotter: an electromechanical device for automatically drawing curves. The curves are generated by a sequence of linear incremental pieces ("vectors") depending on the resolution provided by the device. For cartographic purposes, high precision flat-bed plotters (drawing tables) are used. (b) raster or electrostatic plotter: a sophisticated electronic device for producing pictures by means of raster techniques. The picture is generated by lines of pixels drawn sequentially, typically with a resolution of 200-400 pixels per inch. Raster plotters can produce complete pictures in short time irrespective of the complexity of the picture's contents. [14]
483	Vernier	A short, auxiliary scale situated alongside the graduated scale of an instrument, by means of which fractional parts of the smallest division of the primary scale can be measured accurately. [14]
484	Eyepiece	In an optical device, the lens group which is nearest the eye and with which the image formed by the preceding elements is viewed. [14]
485	Geodesic	See geodesic line. [14]
486	New Moon	See phases of the moon. [14]
487	Open Sea	That part of the ocean not enclosed by headlands, within narrow straits, etc. See high sea. [14]
488	Pinnacle	Any high tower or spire-shaped pillar of rock or coral, alone or cresting a summit. It may extend above the surface of the water. It may or may not be a hazard to surface navigation. [14]
489	Repeater	A device for repeating at a distance the indications of an instrument or device. See compass repeater, gyro repeater, steering repeater. [14]
490	Lead Line	A line, graduated with attached marks and fastened to a sounding lead, used for determining the depth of water when making soundings by hand. Generally used in depths of less than 45 meters (25 fathoms). Lead lines are braided or left-laid. Also called sounding line. [14]
491	Mean Time	See time: mean solar. [14]
492	Shoreline	The line where shore and water meet. Although the terminology of coasts and shores is rather confused, shoreline and coastline are generally used as synonymous. [14]
493	Soft Iron	Iron or steel which is easily magnetized by induction, but loses its magnetism when the magnetic field is removed. The opposite is hard iron. [14]
494	Wire Drag	An apparatus for surveying rocky areas where normal sounding methods are insufficient to insure the discovery of all existing obstructions, pinnacles, rocks, etc., above a given depth or for determining the least depth of an area. It consists essentially of a buoyed wire towed at the desired depth by two launches. Often shortened to drag. See drag (v.t.). [14]
495	Conversion	Determination of the rhumb line direction of one point from another when the initial great circle direction is known, or vice versa. [14]
496	Ebb Stream	The horizontal movement of water associated with falling tide. Ebb streams generally set seaward, or in the opposite direction to the tide progression. Also called ebb, ebb current or outgoing stream. [14]
497	Fair Chart	(British terminology). The final, carefully made plot of a hydrographic survey. In contrast to the field board (boat sheet in US Terminology) which is a work sheet plotted during field operations from preliminary field data, the fair chart is plotted from corrected data and represents the official permanent record of that particular survey. Also called fair sheet. It is called smooth sheet in US Terminology. [14]
498	Graduation	The placing of marks on an instrument or device to represent standard values thereon. Also, the marks so placed. The division and subdivision of latitude and longitude shown on the borders of a chart. See also scale. [14]
499	Grid North	See north. [14]
500	Parametric	Characterizing a quantity which is influenced by the behavior of one or more parameters. [14]
501	Calibration	The act or process of determining certain specific measurements in an instrument or device by comparison with a standard, for the purpose of correcting or compensating errors or for purposes of record. [14]
502	Convergence	In oceanography, a situation whereby waters of different origins come together at a point or, more commonly, along a line known as a convergence line. Along such a line the denser water from one side sinks under the lighter water from the other side. See sinking. [14]
503	Evaporation	The process by which a liquid changes into a gas. [1]
504	Least Depth	The shoalest sounding value obtained on a feature. [14]
505	Storm Surge	A rise above normal water level on the open coast due only to the action of wind stress on the water surface. Storm surge resulting from a hurricane or other intense storm also includes the rise in level due to atmospheric pressure reduction as well as that due to wind stress. A storm surge is more severe when it occurs in conjunction with a high tide. Also called storm tide, storm wave, tidal wave. [14]
506	Thermocline	A vertical negative temperature gradient in some layer of a body of water, which is appreciably greater than the gradients above and below it; also a layer, in which such a gradient occurs. The principal thermoclines in the ocean are either seasonal, due to heating of the surface water in summer, or permanent. Also called discontinuity layer, or thermal layer. [14]
507	Projection: Stereographic	A perspective projection having the point of projection at the opposite end of the diameter of the sphere from the point of tangency of the plane of projection. It is conformal and is the only azimuthal projection having that quality. When the center of the projection is located at a pole of the sphere, it is called a stereographic polar projection; when on the equator, a stereographic meridional projection; and when on some other selected parallel of latitude, a stereographic horizon projection. Also called azimuthal orthomorphic projection. [14]
508	Dew	Deposit of water drops on objects at or near the ground, produced by the condensation of water vapor from the surrounding clear air. [14]
509	Alga	A plant of simple structure which grows chiefly in water, such as the various forms of seaweed. [14]
510	Hail	Precipitation of small balls or pieces of ice (hailstones) with a diameter ranging from 5 to 50 mm (0.2 to 2.0 in) or sometimes more, falling either separately or agglomerated into irregular lumps. [14]
511	Kite	A mechanical contrivance towed beneath the surface to warn of arrival in water of a certain depth. See submarine sentry. A contrivance for holding the inner end of an Oropesa sweep to the required depth. [14]
512	Loop	In oceanography, that part of a standing wave where the vertical motion is greatest and the horizon-tal velocities are least. Loops (sometimes called antinodes) are associated with clapotis and with seiche action resultant from resonant wave reflecting in a harbor or bay. [14]
513	Peak	A prominent elevation either pointed or of very limited extent across the summit. Also called pike. [14]
514	Post	A small beacon, more substantial than a perch, used for marking channels. See also pile. [14]
515	Canal	An artificial waterway with no flow, or a controlled flow, used for navigation or for draining or irrigating land (ditch). [14]
516	Mouth	The place of discharge of a stream into the ocean or entrance to a bay from the ocean. [14]
517	Proof	In cartography, an advanced copy of a map produced to check the design, register and/or to enable errors to be detected and corrected before final printing. [14]
518	Stake	An elongated wood or metal pole embedded in the bottom to serve as a marker or support for fish nets. [14]
519	Aurora	Luminous phenomenon which appears in the high atmosphere, mainly in high latitudes, in the form of rays, arcs, bands, draperies, or corona. Also called polar aurora. [14]
520	Debris	See detritus. [14]
521	Isobar	Line joining points of equal pressure on a given surface (level surface, vertical cross section, etc.). [14]
522	Mirage	Optical phenomenon consisting essentially of steady or wavering, single or multiple, upright or inverted, vertically enlarged or reduced, images of distant objects. [14]
523	Quartz	Crystalline silica. In its most common form it is colourless and transparent, but it takes a large variety of forms of varying degrees of opaqueness and colour. It is the most common solid mineral. Part of the ocean bed is composed of quartz. [14]
524	Shower	Precipitation, often short-lived and heavy, falling from convective clouds; the drops or solid particles in showers are usually bigger than the corresponding elements in other types of precipitation. Showers are characterized by their sudden beginning and ending, generally by large and rapid changes of intensity, and, most frequently, by the appearance of the sky; namely, rapid alternations of dark, menacing clouds (cumulonimbus) and of clearances of short duration. [14]
525	Summit	The highest point, part or elevation; top or apex. [14]
526	Abyssal	Belonging to the lowest depths of the ocean, generally below 3,700 meters (2,000 fathoms). [14]
527	Almanac	A periodical publication of astronomical data useful to a navigator. It contains less information than an ephemeris, and values are generally given to less precision. If information is given in a form and to a precision suitable for air navigation, it is called an air almanac. [14]
528	Geology	The science which has for its object the investigation of the earth's crust, of the strata which enter into its composition with their mutual relations, and of the successive changes to which their present condition and position are due. [14]
529	Ice Cap	See ice sheet. [14]
530	Sea-Bed	See sea floor [14]
531	Shading	Gradations of light, colour, or thickness of lines; or indications of shadows. Shading of lines is sometimes used on charts to produce the effect of height or depth. See also hill shading. [14]
532	Buoyancy	Force resulting from the upward pressure of water, acting upon the immersed volume of a body, set against the total weight of such body. If the volume immersed is such that the upward pressure counterbalances the weight of the body, the buoyancy is said to be positive and the body floats on the surface; if the volume immersed is insufficient, the weight of the body is greater than the upward pressure, the buoyancy is negative, and the body sinks. [14]
533	Coverage	The actual area covered (by charts, photographs, etc.). The area controlled by a radiolocation system. [14]
534	Entrance	The seaward end of a channel, harbor, dock, etc. [14]
535	Pendulum	A body so suspended from a fixed point as to swing freely to and from under the combined forces of gravity and momentum. A vertical bar so supported from below by a stiff spring as to vibrate to and for under the combined action of gravity and the restoring force of the spring. [14]
536	Recorder	The man on a survey party who records the observational data. A recording instrument. The part of an instrument or machine that records. [14]
537	Residual	See error: residual. [14]
538	Sampling	The process of taking samples. [14]
539	Software	All programs which can be used on a computer system. In particular the system software (i.e. The operating system) consists of all programs which are necessary for the proper functioning of the computer. The application software consists of all programs developed for special user applications. [14]
540	Sweeping	The process of towing a line or object below the surface, to determine whether an area is free from isolated submerged dangers to vessels and to determine the position of any dangers that exist, or to determine the least depth of an area. [14]
541	Temporal	(Adj.). Pertaining to or limited by time. [14]
542	Graticule	The network of lines representing meridians and parallels on a map, chart, or plotting sheet. See also grid. A scale at the focal plane of an optical instrument to aid in the measurement of objects. See also reticle. [14]
543	Reflector	A device capable of or intended for reflecting particles or radiant energy. See radar reflector. [14]
544	Sea State	Numerical scale of the average surface wave height as defined by the WMO code. Also called state of the sea. [14]
545	Boat Sheet	(US Terminology). The work sheet used by the hydrographer in the field for plotting the details of a hydrographic survey as it progresses. See also field board. [14]
546	Dip Circle	An instrument for measuring magnetic dip. It consists essentially of a dip needle or magnetic needle, suspended in such manner as to be free to rotate about a horizontal axis. Also called inclinometer, or dipping compass. See also earth inductor. [14]
547	Lapse Rate	The rate at which an atmospheric variable (usually temperature) decreases with height. (see environmental lapse rate.) [1]
548	Pollutants	Any gaseous, chemical, or organic matter that contaminates the atmosphere, soil, or water. [1]
549	True North	See north. [14]
550	Wave Crest	The highest part of a wave. [14]
551	Air Station	N photogrammetry, the point in space occupied by the camera lens at the moment of exposure. Also called exposure station or camera station. [14]
552	Camera Axis	See axis of camera. [14]
553	Datum Plane	A vertical control datum. Although a level surface is not a plane, the vertical control datum is frequently referred to as the datum plane. [14]
554	Gravitation	In general, the mutual attraction between masses of matter (bodies). Gravitation is the component of gravity which acts towards the earth. [14]
555	Large Scale	See scale. [14]
556	Photometeor	Optical phenomenon of the atmosphere. [14]
557	Electromagnetic Waves	Energy propagated in the form of electromagnetic waves. These waves do not need molecules to propagate them, and in a vacuum they travel at nearly 300,000 km per sec (186,000 mi per sec). See radiant energy. [1]
558	Calm	Wind with a speed zero or less than 2 knots (beaufort scale wind force 0). The state of sea when there are no waves. [14]
559	Cape	A piece of land projecting into a body of water. [14]
560	Gage	See gauge: tide. [14]
561	Rose	Name given to a compass card, or other diagram, having radiating lines. [14]
562	Scar	A lofty, steep face of rock upon a mountain-side; a precipice; cliff. [14]
563	Sill	A sea floor barrier of relatively shallow depth restricting water movement between basins. [14]
564	Silt	An unconsolidated sediment whose particles range in size from 0.0039 to 0.0625 millimeters in diameter (between clay and sand size). [14]
565	Awash	Adj. And adv.). Flush with, or washed by the waves. [14]
566	Fetch	An area of the sea surface over which seas are generated by a wind having a constant direction and speed. The length of the generating area, measured in the direction of the wind in which the seas are generated. [14]
567	Locus	(pl. Loci). All possible positions of a point or curve satisfying stated conditions. [14]
568	Noise	Any undesired sound. By extension, noise is any unwanted disturbance within a useful frequency band, such as undesired electric waves in a transmission channel or device. [14]
569	Scarp	The steep face of a hill. See also escarpment. [14]
570	Shell	The hard outside covering of an animal. Part of the ocean bed is composed of numerous shells of marine animals. [14]
571	Slave	A slave station. [14]
572	Title	In cartography, an inscription, on the chart or fair chart, including any useful information and details concerning the hydrographic survey, the natural scale, and geodetic, magnetic and tidal data. [14]
573	Cursor	A device used with an instrument, to provide a movable reference, as the runner of a slide rule, or the rotatable bearing indicator on a radar scope. In computer systems, a highlighted point on the display which indicates the actual working position. For graphical editing special cursors (e.g. Crosses, cross-hairs) can be selected. On output the cursor is moved automatically by the computer; on input it is under user control by means of a manual controlling device. A cursor may also be a manually positionable device, sometimes magnifying lens and a reticula to be used in connection with a digitizer. [14]
574	Freeze	A condition occurring over a widespread area when the surface air temperature remains below freezing for a sufficient time to damage certain agricultural crops. A freeze most often occurs as cold air is advected into a region, causing freezing conditions to exist in a deep layer of surface air. Also called advection frost. [1]
575	Lagoon	An enclosed area of salt or brackish water separated from the open sea by some more or less effec-tive, but not complete, obstacle such as low sand bank. The name most commonly used for the area of water enclosed by a barrier reef or atoll. [14]
576	Pascal	The unit of pressure in the si system. [14]
577	Piling	A group of piles set in a row. [14]
578	Rocket	In hydrography or navigation, a pyrotechnic projectile used for signaling, or for life-saving purposes. [14]
579	Draught	See draft. [14]
580	Erosion	The general process of the wearing away of rocks and soil at the earth's surface by natural agencies. [14]
581	Iceberg	A large mass of floating or stranded ice broken away from a glacier or from an ice shelf. Often of considerable height (in any case more than 5 m above the level of the sea). [14]
582	Inshore	(Adj. And adv.). Near or towards the shore. [14]
583	Landing	A place where boats receive or discharge passengers, freight, etc. [14]
584	Profile	A graph or curve showing elevation or distribution of some property vs. Distance along a line. The vertical scale may be greatly exaggerated with respect to the horizontal scale. An example of a profi-le is the graphic record made by a recording echo sounder operating while a vessel is underway. A vertical section of the surface of the ground, or of underlying strata, or both, along any fixed line. [14]
585	Snapper	A bottom sampling device used to collect a small amount (less than 1 pint) of material from the ocean floor. It has metal jaws that snap shut when the device touches the bottom. Also called clam shell snapper. [14]
586	Storage	In a computer, a device in which data can be inserted and preserved, and from which data can be retrieved. Common storage devices are magnetic tapes, drums, disks and cores. [14]
587	Terrain	Standing ground. A tract of country considered with regard to its natural features, configuration, etc. [14]
588	Emulsion	In photography, a suspension of a salt of silver in gelatine or collodion, used to coat plates, films, or papers. [14]
589	Fast Ice	Sea ice which remains fast, generally in the position where originally formed, and which may attain a considerable thickness. It is found along coasts, where it is attached to the shore, or over shoals, where it may be held in position by islands, grounded icebergs or grounded polar ice. [14]
590	Millibar	A unit of pressure equal to 1/1,000 of a bar. The millibar is much used in meteorology. [14]
591	Momentum	Quantity of motion. That property of a particle which is given by the product of its mass with its velocity. [14]
592	Monument	(US Terminology). In surveying, a structure used or erected to mark the position of a station; permanence is implied. [14]
593	Resurvey	A retracing on the ground of the lines of an earlier survey, in which all points of the earlier survey that are recovered are held fixed and used as a control. If too few points of the earlier survey are recovered to satisfy the control requirements of the resurvey, a new survey may be made. A resurvey is related directly to an original survey although several resurveys may interpose between them. [14]
594	Swath(E)	The strip or lane on the ground or sea floor scanned by the swath(e) sounding system when the survey platform proceeds along its course. [14]
595	Clearance	In navigation, a safe distance off a danger. In meteorology: a) decrease of total cloud amount when the latter is large; b) time at which this decrease takes place; c) gap in a cloud layer covering the entire sky. Also called clearing. [14]
596	Ephemeris	A statement presenting positions and related data for a celestial body for given epochs (dates) at uniform intervals of time. Also a publication containing such data for a number of celestial bodies. See also almanac: air and almanac: nautical. [14]
597	Gas Field	An area in which natural gas occurs in quantities worthy of exploitation. [14]
598	Hand Lead	See lead. [14]
599	Hyperbola	An open curve with two parts, all points of which have a constant difference in distance from two fixed points called foci. [14]
600	Ice Sheet	A continuous mass of ice and snow of considerable thickness and large area. Ice sheets may be resting on rock (see inland ice sheet) or floating (see ice shelf). Ice sheets of less than 40,000 sq. Km resting on rock are called ice caps. [14]
601	Indicator	That part of electronic equipment in which the data obtained by the receiver is presented for visual observation. This is usually in the form of a scope or dial. [14]
602	Intercept	The name given in marcq St. Hilaire method to the difference between the calculated altitude and the true altitude of a celestial body. Also called altitude difference. [14]
603	Isocentre	The unique point common to the plane of a photograph, its principal plane, and the plane of an assumed truly vertical photograph taken from the same camera station and having an equal principal distance. The point of intersection on a photograph of the true principal line and the isometric parallel. The point on a photograph intersected by the bisector of the angle between the plumb line and the photograph perpendicular. The isocenter is significant because it is the center of radiation for displacements of images caused by tilt. [14]
604	Messenger	In oceanographic terminology, a cylindrical metal weight, usually hinged and with a latch so that it can be fastened around a wire, and sent down to actuate water bottles and current meters after they have been lowered to the desired depth. [14]
605	Neat Line	Line, usually grid or graticule, bounding the detail of a map. Also referred to as inner neat line to differentiate from border drawn outside of neat line. Also written as one word. [14]
606	Omnirange	A radio aid to navigation providing direct indication of the magnetic bearing (omnibearing) of that station from any direction. Also called omnidirectional range or omnidirectional beacon. [14]
607	Projector	An optical instrument which throws the image of a negative or print upon a screen or other viewing surface, usually at a larger scale. An underwater acoustic transmitter. See underwater sound projector. [14]
608	Si System	See systems international. [14]
609	Sound Ray	A line perpendicular at each of its points to the fronts of a sound wave. [14]
610	Sub-Point	That point on the surface of the earth at which a particular celestial body is in the zenith at a specified time. Also called 'geographical position of a celestial body'. Called sub-celestial point in canadian terminology. See sublunar point, subsolar point, substellar point. [14]
611	Vibration	Periodic motion of an elastic body or medium in alternately opposite directions from equilibrium; oscillation. The motion of a vibrating body during one complete cycle; two oscillations. [14]
612	Anchor Ice	Ce which is attached to the bottom, irrespective of the nature of its formation. Also called bottom ice, depth ice, ground ice, lappened ice and underwater ice. [14]
613	Collimator	An optical device for artificially creating a target at infinite distance (a beam of parallel rays of light) used in testing and adjusting certain optical instruments. It usually consists of a converging lens and a target (a system or arrangement of cross hairs) placed at the principal focus of the lens. [14]
614	Hydrophone	An electroacoustic transducer that responds to water-borne sound waves and delivers essentially equivalent electric waves. See also pressure hydrophone. [14]
615	Plumb Line	The line of force in the geopotential field. The continuous curve to which the direction of the normal gravity is everywhere tangential. [14]
616	Quadrature	An elongation of 90° usually specified as east or west in accordance with the direction of the body from the sun. The moon is at quadrature at first and last quarters. See phases of the moon. The situation of two periodic quantities differing by a quarter of a cycle. [14]
617	Scale: Bar	A graduated line on a map, plan, photograph, or mosaic, by means of which actual ground distances may be determined. Also called graphic scale or linear scale. [14]
618	Scattering	In physics, the change in direction of a particle or wave, because of a collision with another particle or system. In electromagnetism, diffusion of electromagnetic waves in a random manner by air masses in the upper atmosphere. See also: tropospheric scattering. [14]
619	Tide Gauge	See gauge. [14]
620	Turbulence	A state of fluid flow in which the instantaneous velocities exhibit irregular and apparently random fluctuations, so that in practice only statistical properties can be recognized and submitted to analysis. Superimposed on the mean motion of the air, an agitation composed of air motions which are uncoordinated and in a state of continuous change. [14]
621	Wave Front	The leading side of a wave. [14]
622	Bathymetric	(Adj.). Of or pertaining to bathymetry. [14]
623	Field Board	(British terminology). Wooden board, or zinc or plastic sheet, used by hydrographers and land surveyors for plotting and recording the details of the survey in the field. Separate boards are usually prepared for topography and sounding respectively. The former are referred to as topography boards; the latter as sounding boards. See also boat sheet, and plane table. [14]
624	Image Point	In photogrammetry, the image on a photograph corresponding to a definite object on the ground. [14]
625	Inclination	The angle which a line or surface makes with the vertical, horizontal or with another line or surface. [14]
626	Instability	Property of the state of rest or continuous movement of a system such that any disturbance intro-duced into this state grows. In meteorology, the term is often used as a synonym of static instability. [14]
627	Slack Water	The interval when the speed of the tidal current is very weak or zero; usually refers to the period of reversal between ebb and flood currents. Also called slack tide. [14]
628	Tidal Datum	See datum. [14]
629	Trade Winds	Persistent winds, mainly in the lower atmosphere, which blow over vast regions from a subtropical anticyclone toward the equatorial regions. The predominant directions of the trade winds are from ne in the northern hemisphere and from se in the southern hemisphere. [14]
630	True Course	See course. [14]
631	Celestial Coordinates	See coordinates. [14]
632	Apex	The top, peak, or highest point of something, as of a mountain. See also vertex. [14]
633	Berm	A narrow, raised path or embankment along a stream, canal, or beach. On a beach it may be formed by the deposit of material by waves and marks the limit of high tides. [14]
634	Boom	A floating barrier used to protect a river or harbor mouth or to create a sheltered area for storage purposes. [14]
635	Byte	A unit consisting of 8 bits, frequently used for measuring the capacity of storage devices. 1 Kbyte = 210 byte = 1.024 byte (kilo-byte); 1 Mbyte = 220 byte = 1.048.576 byte (mega-byte); 1 Gbyte = 230 byte = 1.073.741.824 byte (giga-byte). [14]
636	Drum	A rotating cylinder on which is set a registering card or paper for recording purposes. Cylinder around which cable is wound in a winch. [14]
637	Eddy	A circular movement of water usually formed, where currents pass obstructions, between two adjacent currents flowing counter to each other, or along the edge of a permanent current. [14]
638	Foul	(1) to entangle or become entangled; e.g. As a propeller becoming entangled in cables, nets, or seaweed. (2) to attach or come to lie on the surface of submerged objects, usually in large numbers or amounts as barnacles on the hull of a ship. [14]
639	Isle	An island. Now more usually applied to an island of smaller size, except in established appellation, as the 'British isles'. [14]
640	Kelp	One of an order of usually large blade-shaped or vinelike brown algae. [14]
641	Lava	The fluid or semi-fluid matter flowing from a volcano. The substance that results from the cooling of the molten rock. Part of the ocean bed is composed of lava. [14]
642	Loom	The glow of a light which is below the horizon, caused by reflection by solid particles in the air. Vague first appearance of land at sea. [14]
643	Pool	A small body of still or standing water, permanent or temporary; chiefly one of natural formation. A deep or still place in a river or stream. In ice terminology, any enclosed relatively small area in pack ice, drift ice, other than a lead. See polynia. [14]
644	Ruin	A ruin is a structure in a decayed or deteriorated condition resulting from neglect or disuse, or a damaged structure in need of repair. A ruin is considered hazardous if it extends over or into navigable waters and thus represents a danger to surface navigation. [14]
645	Slip	See dock. [14]
646	Beset	(Adj.). Of a ship when surrounded so closely by sea ice that steering control is lost. The term does not imply pressure. See also icebound, nipped. [14]
647	Brook	A small stream; a rivulet. Also called run. [14]
648	Comet	A heavenly body having a starlike nucleus with a luminous foggy envelope (see coma), and usually developing a long luminous tail when near the sun. [14]
649	Diver	A person skilled in the practice of diving. [14]
650	Fault	In geology, a break of shear in the earth's crust with an observable displacement between the two sides of the break, and parallel to the plane of the break. [14]
651	Gauss	The cgs unit of magnetic induction. [14]
652	Haven	An enclosed and protected harbor. [14]
653	Inset	In cartography: a) a small area outside the neat lines of a map or chart included within the neat lines or borders to avoid publishing a separate graphic of the small area alone; b) a representation of a small area on a larger scale (e.g., town-plan inset), or of a large area at a smaller scale (e.g., orientati-on inset); c) any information, not normally appearing within the geographic limits of a map, which has been enclosed by border lines and included within the map neat lines. Insets are always placed in areas where important features will not be obscured. [14]
654	Invar	An alloy of nickel and steel which has a low coefficient of expansion. [14]
655	Ledge	A shelf-like projection, on the side of a rock or mountain. A rocky formation continuous with and fringing the shore. [14]
656	Magma	The molten material in a state of fusion under the crust of the earth from which igneous rocks are formed. [14]
657	Pixel	Contraction for "picture element". The smallest element resolvable by electronic raster devices such as scanner, display, and plotter. See remote sensing. [14]
658	Racon	A radar beacon which returns a coded signal which provides identification of the beacon as well as range and bearing. The range and bearing are indicated by the location of the first character received on the radar ppi scope. The name 'racon' is derived from the words radar beacon. [14]
659	Slush	An accumulation of ice crystals which remain separate or only slightly frozen together. It forms a thin layer and gives the sea surface a greyish or leaden-tinted colour. With light winds no ripples appear on the surface. [14]
660	Spire	A pointed structure extending above a building. The spire is seldom less than two‘ thirds of the entire height and its lines are rarely broken by stages or other features. The term is not applied to short pyramid-shaped structures rising from a tower or belfry. [14]
661	Spout	Phenomenon consisting of an often violent whirlwind, revealed by the presence of a cloud column or inverted cloud cone (funnel cloud), protruding from the base of a cumulonimbus and of a 'bush' composed of water drops raised from the surface of the sea or of dust, sand, or litter, raised from the ground. [14]
662	Swamp	An area of spongy land saturated with water. It may have a shallow covering of water, usually with a considerable amount of vegetation appearing above the surface. [14]
663	Apogee	That orbital point farthest from the earth when the earth is the center of attraction, as opposed to perigee. [14]
664	Binary	The number system using 2 as the base for number representation. Binary numbers are composed of bits. Generally any element capable of only two mutually exclusive states is called binary. [14]
665	Comber	A deep water wave whose crest is pushed forward by a strong wind and is much larger than a whitecap. Also called beach comber. A long-period spilling breaker. See also roller. [14]
666	Filter	In optics, any transparent material which, by absorption, selectively modifies the light transmitted through an optical system. In ocean-wave forecasting, a set of formulas that define the particular wave frequencies and directions in the fetch area which are of significance at the point of forecast. [14]
667	Hollow	Trough or depression between crests of sea-waves. A cavity or hole. [14]
668	Launch	Large open or half decked boat. [14]
669	Ripple	The ruffling of the surface of water, hence a little curling wave or undulation. A wave controlled to a significant degree by both surface tension and gravity. [14]
670	Roller	An indefinite term, sometimes considered to denote one of a series of long-crested, large waves which roll in upon a coast, as after a storm. Large breakers on exposed coasts formed by swell coming from a great distance. See comber. [14]
671	Runway	A defined rectangular area, on a land aerodrome, prepared for the landing and take-off run of aircraft along its length. [14]
672	Sludge	Spongy whitish ice lumps, a few centimeters across; they consist of slush, of snow slush and some-times of spongy ice lumps formed on the bottom of the sea and emerging on the surface. [14]
673	Squall	Atmospheric phenomenon characterized by a very large variation of wind speed: it begins suddenly, has a duration of the order of minutes, and decreases rather suddenly in speed. It is often accom-panied by a shower or thunderstorm. (WMO classification squall requires wind speed to increase by at least 8m/s, top speed of at least 11m/s, and lasting at least 1 minute in duration) [14]
674	Strand	(v.t. & i.). To run aground. The term strand usually refers to a serious grounding, while the term ground refers to any grounding, however slight. [14]
675	Tripod	A three-legged stand for theodolite, camera, signals, etc. [14]
676	Uprush	The rush of water up onto the beach following the breaking of a wave. See run-up. [14]
677	Zodiac	The band of the sky extending 8.5° either side of the ecliptic. The sun, moon, and navigational planets are always within this band, with the occasional exception of Venus. The zodiac is divided into 12 equal parts, called 'signs', each part being named for the principal constellation originally within it. [14]
678	Aground	Touching, resting or lodged on the bottom of shallow water. The opposite is afloat. [14]
679	Blunder	See error: gross. [14]
680	Caisson	A steel structure used for closing the entrance of locks, wet and dry docks. See also lock gate. [14]
681	Culture	All features constructed on the surface of the earth by man, such as cities, railways, canals, etc. [14]
682	Cumulus	A cloud in the form of individual, detached domes or towers that are usually dense and well defined. It has a flat base with a bulging upper part that often resembles cauliflower. Cumulus clouds of fair weather are called cumulus humilis. Those that exhibit much vertical growth are called cumulus congestus or towering cumulus. [1]
683	Fairway	That part of a river, harbor etc. Where the main navigable channel for vessels of larger size lies. It is also the usual course followed by vessels entering or leaving harbors and sometimes called ship channel . [14]
684	Looming	An apparent elevation of distant terrestrial objects by abnormal atmospheric refraction. Because of looming, objects below the horizon are sometimes visible. The opposite is sinking. The appearance indistinctly of an object during a period of low visibility. [14]
685	Navarea	The short title for a geographical sea area (may include inland seas, lakes and waterways navigable by sea-going ships) established for the purpose of coordinating the broadcast of navigational warnings. The term navarea followed by a roman numeral may be used to identify a particular sea area. The delimitation of such areas is not related to and shall not prejudice the delimitation of any boundaries between states. [14]
686	Outflow	The flow of water from the river or its estuary to the sea. Total volume for any given period of time. [14]
687	Pelorus	A compass card in the form of a metal plate mounted in gimbals to maintain a horizontal position and fitted with sight-vanes for observing bearings where direct use of the compass for this purpose is impracticable. Also called dumb compass or bearing plate. See also alidade. [14]
688	Plateau	A flat or nearly flat elevation of considerable areal extent, dropping off abruptly on one or more sides; a tableland. [14]
689	Plummet	A sounding lead. A plumb bob. [14]
690	Subsoil	All naturally occurring matter lying beneath the sea-bed or deep ocean floor. [14]
691	Tsunami	A long-period sea wave produced by a submarine earthquake or volcanic eruption. It may travel unnoticed across the ocean for thousands of miles from its point of origin. It builds up to great heights over shoal water. Also called tsunami, tidal wave, seismic sea wave. [14]
692	Aerosols	Tiny suspended solid particles (dust, smoke, etc.) Or liquid droplets that enter the atmosphere from either natural or human (anthropogenic) sources, such as the burning of fossil fuels. Sulfur-containing fossil fuels, such as coal, produce sulfate aerosols. [1]
693	Asteroid	One of the many small planets revolving around the sun, most of the orbits being between those of mars and jupiter. Also called planetoid or minor planet. [14]
694	Dry Dock	See dock. [14]
695	Envelope	In electronics, a graph defining the variations in amplitude of successive oscillations in an amplitude-modulated wave. [14]
696	Guidance	The exercise of directing influence over the movements of a craft or missile with particular refe-rence to the selection of a flight path. [14]
697	Ice Edge	The boundary at any given time between the open sea and sea ice of any kind, whether drifting or fast. [14]
698	Inmarsat	A company providing mobile satellite communications. The only company (2011) providing services within the gmdss. [14]
699	Land Ice	See glacier ice. [14]
700	Log Line	A graduated line used to measure the speed of a vessel through the water or to measure the speed of a current from a vessel at anchor. The line secured to a log. See current pole. [14]
701	Obscured	(Adj.). Said of the arc of a light sector designated by its limiting bearings in which the light is not visible from seaward. [14]
702	Pipeline	A string of interconnected pipes used for the transport of matter, nowadays mainly oil or gas . [14]
703	Scribing	A method of preparing a map by cutting the lines into a prepared coating. [14]
704	Streamer	A string of hydrophones towed behind a ship. [14]
705	Tracking	The process of observing the sequential changes in the position of a target to establish its motion. [14]
706	Uncovers	See covers and uncovers. [14]
707	Accretion	The gradual building up of land over a long period of time, solely by the action of the forces of nature, on a beach by deposition of water or air-borne material. Artificial accretion is a similar build-up of land by reason of an act of man. Also called aggradation. [14]
708	Alignment	The placing of objects along a straight line. In navigation, the bringing into line of two or more conspicuous objects, such as lights, beacons, etc. Also their bearing as seen by an observer from seaward. [14]
709	Astrolabe	An instrument formerly used for measuring altitudes of celestial bodies. See astrolabe: prismatic. [14]
710	Date Line	The line coinciding approximately with the 180th meridian, at which each calendar day first begins, the boundary between the -12 and +12 time zones. The date on each side of this line differs by one day, but the time is the same in these two zones. Sometimes called calendar line or international date line. [14]
711	Full Moon	See phases of the moon. [14]
712	Heliostat	An instrument composed of one or more plane mirrors, so mounted and arranged that a beam of sunlight may be reflected by it in any desired direction and kept there by continuous adjustment. It is used in geodetic surveying for reflecting a beam of sunlight from a station towards another distant station, where it can be observed with a theodolite. Also called heliotrope, or Galton’s sun signal. [14]
713	High Seas	The open sea beyond the exclusive economic zone, the territorial sea or the archipelagic waters of an archipelagic state. [14]
714	Ice Cover	See ice concentration. [14]
715	Interface	A surface, usually plane, forming the boundary between adjacent solids, spaces or immiscible liquids. In data processing it describes all information (signals, data) and the specifications ("protocol") required for exchanging data between two units of a system. Interfaces exist between hardware and software units but also between computer and human user. [14]
716	Lightship	A distinctively marked vessel anchored or moored at a charted point, to serve as an aid to navigation. By night it displays a characteristic light(s), and is usually equipped with other devices, such as a fog signal, submarine sound signal, and radio beacon, to assist navigation. Also called light vessel. [14]
717	Microwave	A very short radio wave, usually 30 cm to 0.3 mm. [14]
718	Polar Low	Depression that forms in polar air, often near a boundary between ice and sea. [15]
719	Resection	The graphical or analytical determination of a position as the intersection of at least three lines of known relative direction to corresponding points of known position. In photogrammetry, the determination of the position and/or attitude of a camera, or the photograph taken with that camera, with respect to the exterior coordinate system. [14]
720	Roadstead	An area near the shore, where vessels can anchor in safety; usually a shallow indentation in the coast. Also called road or roads. See open roadstead. [14]
721	Wave: Sky	An indirect radio wave which travels from the transmitting antenna into the sky, where the ionosphere bends it back toward the earth. Also called ionospheric wave. See wave: ground. [14]
722	Zone Time	See time. [14]
723	Cold Front	Any non-occluded front which moves in such a way that colder air replaces warmer air. [14]
724	Coral Reef	A reef, often of large extent, composed chiefly of coral and its derivatives. [14]
725	Degaussing	Neutralization of the strength of the magnetic field of a vessel, by means of suitably arranged electric coils permanently installed in the vessel. See also cable: degaussing. [14]
726	Earthquake	A shaking or trembling of the crust of the earth caused by underground volcanic forces or by breaking and shifting of rock beneath the surface. [14]
727	Elongation	The angular distance of a body of the solar system from the sun. The angle at the earth between lines to the sun and another celestial body of the solar system. The term is usually used in connection with inferior planets. The greatest elongation of such a body is its maximum angular distance from the sun, as observed from the earth. The position of a star when its azimuth east or west of the meridian is greatest. [14]
728	Fish Haven	Areas established by private interests, usually sport fishermen, to simulate natural reefs and wrecks that attract fish. The reefs are constructed by dumping assorted junk in areas which may be of very small extent or may stretch a considerable distance along a depth contour. Fish havens are outlined and labeled on charts. Also called fishery reefs. [14]
729	Fixed Star	A star. The expression is used particularly to distinguish stars from other heavenly bodies; so called by ancients to distinguish stars from the wandering planets. [14]
730	Ionosphere	That part of the atmosphere, extending from about 70 to 500 km, in which ions and free electrons exist in sufficient quantities to reflect electromagnetic waves. [14]
731	Jet Stream	Relatively strong winds concentrated within a narrow band in the atmosphere. [1]
732	Local Time	See time. [14]
733	Neap Range	The mean semidiurnal range of tide when neap tides are occurring; the mean difference in height between neap high water and neap low water. Sometimes called mean neap range. [14]
734	Neap Tides	Tides of decreased range or tidal currents of decreased speed occurring semimonthly as the result of the Moon being in quadrature. The neap range (Np) of the tide is the average range occurring at the time of neap tides and is most conveniently computed from the harmonic constants. It is smaller than the mean range where the type of tide is either semi diurnal or mixed and is of no practical significance where the type of tide is predominantly diurnal. The average height of the high waters of the neap tide is called neap high water or high water neaps (MHWN) and the average height of the corresponding low waters is called neap low water or low water neaps (MLWN). [22]
735	Opposition	The situation of two periodic quantities differing by half a cycle. In astronomy, the situation of two celestial bodies having either celestial longitudes or sidereal hour angles differing by 180°. The term is usually used only in relation to the position of a superior planet or the moon with reference to the sun. [14]
736	Polar Axis	See axis. [14]
737	Resolution	The separation by an optical system of parts of an object or of two or more objects close together. The degree of ability to make such a separation, called resolving power, is expressed as the minimum distance between two objects that can be separated. The degree of ability of a radar set to indicate separately the echoes of two targets in range and bearing. [14]
738	Saturation	The condition existing when the greatest possible amount of anything has been reached, as a magnetic substance which cannot be further magnetized, or an electronic aid to navigation which is being used by all the craft it can handle. At given temperature and pressure, state of moist air whose mixing ratio is such that the moist air can co-exist in neutral equilibrium with an associated condensed phase (liquid or solid) at the same temperature and pressure, the surface of separation being plane. [14]
739	Small Halo	See halo. [14]
740	Wire Angle	The angle measured between the sounding wire, or the oceanographic wire, and the vertical. [14]
741	Conspicuous	Adj.). Term applied to an object either natural or artificial which is distinctly and notably visible from seaward. [14]
742	Core Barrel	The tubular section of a core sampling device. Bottom sediment samples are collected either directly in the core barrel or in a plastic liner placed inside it. Also called coring (or core) tube. [14]
743	Culmination	The position of a heavenly body when at highest apparent altitude. Also, for a heavenly body which is continually above the horizon, the position of lowest apparent altitude. Culmination occurs when the body transits the local meridian. See meridian transit. [14]
744	Drift Angle	The difference between course steered and course made good when due to action of current and wind. The angle between the tangent to the turning circle and the centerline of the ship. [14]
745	Fathom Line	A depth curve with depth expressed in fathoms. Also called fathom curve, isobath. [14]
746	Hydrography	Hydrography is the branch of applied sciences which deals with the measurement and description of the physical features of oceans, seas, coastal areas, lakes and rivers, as well as with the prediction of their change over time, for the primary purpose of safety of navigation and in support of all other marine activities, including economic development, security and defence, scientific research, and environmental protection. [14]
747	Lens System	The combination of two or more lenses placed in series on the same principal axis. [14]
748	Lunar Month	See month: synodical. [14]
749	Maintenance	All procedures and activities required to keep equipment operational. [14]
750	Meteorology	Science of the atmosphere. [14]
751	Nadir Point	See nadir: photograph. [14]
752	Retardation	In electronic navigation, the amount of delay in time or phase angle introduced by the resistivity of the ground over which the signal is passing. In tide terminology, daily retardation. [14]
753	Thermograph	Thermometer used to give a graphical record of the time variations of temperature. [14]
754	Tide Tables	Tables listing daily predictions, usually a year in advance, of the times and heights of the tide. These predictions are usually supplemented by tidal differences and tidal constants by means of which additional predictions can be obtained for numerous other places. See tide prediction. [14]
755	Troposphere	Lower part of the terrestrial atmosphere, extending from the surface up to a height varying from about 9 km at the poles to about 17 km at the equator, in which temperature decreases fairly regularly with height. From an analogy with the atmosphere, the term is sometimes applied in oceanography to the upper ocean layer of relatively high temperature that is found in middle and lower latitudes and within which strong currents are present. See stratosphere. [14]
756	Ultraviolet	(Adj.). Having a frequency immediately beyond the violet end of the visible spectrum. Said of rays of shorter wavelength than visible light but longer than x-rays. [14]
757	Environmental Lapse Rate	The rate of decrease of air temperature with elevation. It is most often measured with a radiosonde. [1]
758	Gap	A narrow break in a ridge or rise. [14]
759	Key	See cay. [14]
760	MSL	Mean Sea Level (MSL) ; The arithmetic mean of hourly heights observed. Shorter series are specified in the name; e.g. monthly mean sea level and yearly mean sea level. [21]
761	Sac	An indentation in the contours on a chart showing submarine relief which is analogous to a gulf on the surface. The opposite term is submarine peninsula. [14]
762	Dyne	The unit of force in the cgs system. [14]
763	Gulf	A part of the sea extending into the land, usually larger than a bay. [14]
764	Menu	A list of commands and/or options. The user selects the desired command by moving the cursor to the respective position on the menu or by entering an appropriate code at the command entry line of the display. [14]
765	MHWN	Mean High Water Neaps (MHWN) ; The height of mean high water neaps is the average throughout the year (when the average maximum declination of the moon is 23.5°) of two successive high waters during those periods of 24 hours when the range of the tide is at its least. The values of MHWN vary from year to year with a cycle of approximately 18.6 years. [24]
766	MHWS	Mean High Water Springs (MHWS) ; The height of mean high water springs is the average throughout the year (when the average maximum declination of the moon is 23.5°) of two successive high waters during those periods of 24 hours when the range of the tide is at its greatest. The values of MHWS vary from year to year with a cycle of approximately 18.6 years. [24]
767	MLWN	Mean Low Water Neaps (MLWN) ; The height of the mean low water neaps is the average height obtained by the two successive low waters during periods of 24 hours when the range of the tide is at its least. The values of MLWN vary from year to year with a cycle of approximately 18.6 years. [24]
768	MLWS	Mean Low Water Springs (MLWS) ; The height of mean low water springs is the average throughout the year (when the average maximum declination of the moon is 23.5°) of two successive high waters during those periods of 24 hours when the range of the tide is at its greatest. The values of MLWS vary from year to year with a cycle of approximately 18.6 years. [24]
769	Quay	A wharf approximately parallel to the shoreline and accommodating ships on one side only, the other side being attached to the shore. It is usually of solid construction, as contrasted with the open pile construction usually used for piers. [14]
770	Tank	A fixed structure for storing liquids. [14]
771	Tuff	A rock formed of fragments of volcanic origin, dust, ashes, etc., thrown out of a volcano during an eruption, frequently hardened to a rock. Hence tuff-cone, a volcanic cone built up of such material. [14]
772	Yard	A unit of length equal to 3 feet, 36 inches, or 0.9144 metre. [14]
773	Abeam	In a line approximately at right angles to the ship's keel; also: the waist or middle part of the ship. [14]
774	Agger	See tide: double. [14]
775	Delta	An area of alluvial deposit, usually triangular in outline, near the mouth of a river. [14]
776	Inlet	A narrow opening by which the water penetrates into the land. [14]
777	Islet	A small island. [14]
778	Jetty	In US Terminology, a structure, such as a wharf or pier, so located as to influence current or protect the entrance to a harbor or river. In British terminology, a pier, usually of solid construction, intended as a berthing place for vessels. See dock, landing, wharf. [14]
779	Laser	Light amplification by stimulated emission of radiation. A device that produces an intense beam of monochromatic, spatially coherent light. [14]
780	Levee	A depositional natural embankment bordering a canyon, valley or sea channel on the ocean floor. [14]
781	Lidar	(light detection and ranging) an instrument that measures distance to a reflecting object by emitting timed pulses of laser light and measuring the time between emission and reception of reflected pulses. The measured time interval is converted to distance. In survey use, the lidar system usually scans the light pulses across the track of the survey platform (usually an aircraft) so that successive pulses cover a swath(e) either side of the platform's track. Infra-red lasers will reflect off land and water and are normally used for topographic lidar surveys. Blue-green lasers will penetrate water and are used in hydrographic lidar surveys. [14]
782	Probe	Any device inserted in an environment for the purpose of obtaining information about the environ-ment. [14]
783	Siren	A type of fog signal apparatus which produces sound by virtue of the passage of air through slots or holes in a revolving disk. [14]
784	Spoil	Mud, sand, silt or other deposit obtained from the bottom of a channel or harbor by dredging. [14]
785	Swash	A narrow channel or sound within a sand bank, or between a sand bank and the shore. Also called swash way. A bar over which the sea washes. The rush of water up onto a beach following the brea-king of a wave. [14]
786	Trend	The general direction of something, such as a coastline. [14]
787	Canyon	A relatively narrow, deep depression with steep sides, the bottom of which generally has a continuous slope. [14]
788	Careen	Causing a vessel to lie over on one side. [14]
789	Drogue	A current measuring assembly consisting of a weighted parachute and an attached surface buoy. Also called parachute drogue. [14]
790	Isogon	Line which is the locus of points at which the direction of wind is the same. [14]
791	Isopor	See isoporic line. [14]
792	Legend	A description, explanation, table of symbols, and other information, printed on a map or chart to provide a better understanding and interpretation of it. The title of a map or chart formerly was considered part of the legend, but this usage is obsolete. [14]
793	Matrix	In oceanography, rock or sediment in which larger grains are embedded in a mass of smaller grains. In printing, a metal plate, usually of copper, for moulding the face of a type. In graphic arts, a mold in which type characters are cast in line-casting machines and foundry type. [14]
794	Medusa	See coelenterate and jellyfish. [14]
795	Nebula	(pl. Nebulae). An aggregation of matter outside the solar system, large enough to occupy a perceptible area but which has not been resolved into individual stars. [14]
796	Occupy	(v.t.). In surveying, to observe with a surveying instrument at a station; also, to set a surveying instrument over a point for the purpose of making observations. In oceanography, to stop a ship at a selected location, an oceanographic station, for the purpose of gathering oceanographic observations. [14]
797	Offset	In surveying, a short line perpendicular to a surveyed line, measured to a line or point for which data are desired, thus locating the second line or point with reference to the first or surveyed line. An offset is also a jog in a survey or other line, the line having approximately the same direction both before and after passing the jog. Offsets are measured from a surveyed line or lines to the edges of an irregular-shaped body of water, or to any irregular line which it is desired to locate. [14]
798	P-Code	The precise (or protected) gps code; a very long (about 1014 bit) sequence of pseudo-random binary biphase modulations on the gps carrier at a chip rate of 10.23 MHz which does not repeat itself for about 267 days. Each one-week segment of the p-code is unique to one gps satellite and is reset each week. See also c/a code. [14]
799	Ramark	A radar marker beacon which continuously transmits a signal appearing as a radial line on the ppi, the line indicating the direction of the beacon. Ramarks are intended primarily for marine use. The name 'ramark' is derived from the words radar marker. [14]
800	Regime	In climatology, term used to characterize the seasonal distribution of one or more elements at a given place. [14]
801	Ruling	A mechanically produced series of equally spaced parallel lines at a predetermined 'angle of ruling'. Used to distinguish particular areas of a map by providing a paler shade of the full printing colour. [14]
802	Run-Up	The rush of water up a structure on the breaking of a wave. The amount of run-up is the vertical height above still water level that the rush of water reaches. See uprush. [14]
803	Seaway	A moderately rough sea. Used chiefly in the expression 'in a seaway'. Headway of a vessel. The sea as a route of travel from one place to another; a shipping lane. [14]
804	Sinker	Weight used to sink fishing line or sounding line. [14]
805	Strand	The portion of the seashore between high and low water line. [14]
806	Taping	The operation of measuring a distance on the ground using a tape or ribbon of metal or other material. Also called chaining. [14]
807	Tracer	Foreign substance introduced into the water by natural or artificial means which enables determination of water movement through measurement of distribution and location of the substance at the same time. [14]
808	Y-Axis	A vertical axis in a system of rectangular coordinates; that line on which distances above or below (north or south of) a reference line are marked, especially on a map, chart, or graph. The line which is perpendicular to the x-axis and passes through the origin. [14]
809	Bay Ice	Level fast ice of more than one winter's growth, which may be nourished by surface layers of snow. Thickness of ice and snow up to about 2 m above sea level. When bay ice becomes thicker than this, it is called an ice shelf. [14]
810	Bedrock	Any solid rock underlying soil or unconsolidated sediments. [14]
811	Calorie	A unit of quantity of heat, originally defined as the amount of heat required to raise the temperature of one gram of water through one degree c. The 15-degree gram-calorie is the amount of heat required to raise the temperature of one gram of water from 14°.5 c to 15°.5 c and is equal to 4.1855 joules. [14]
812	Candela	The unit of luminous intensity in the si system. [14]
813	Daymark	1. The identifying characteristics of an aid to navigation which serve to facilitate its recognition against a daylight viewing background. On those structures that do not by themselves present an adequate viewing area to be seen at the required distance, the aid is made more visible by affixing a daymark to the structure. A daymark so affixed has a distinctive colour and shape depending upon the purpose of the aid. 2. An unlighted navigational mark. [14]
814	Dolphin	A post or group of posts, used for mooring or warping a vessel, or as an aid to navigation. The dolphin may be in the water, on a wharf or on the beach. [14]
815	El Niño	An extensive ocean warming that begins along the coast of peru and ecuador and extends westward over the tropical pacific. Major el niño events, or strong el niños, occur once every 2 to 7 years as a current of nutrient-poor tropical water moves southward along the west coast of south america. [1]
816	Gimbals	A device consisting of two rings pivoted at right angles to each other, for supporting anything, such as an instrument, in such a manner that it will remain essentially horizontal when the support tilts. Also called cardanic suspension. [14]
817	Glonass	A space-based, radio-positioning, navigation and time-transfer system operated by the government of the russian federation. Glonass to which differential corrections have been applied is known as differential glonass (dglonass). See also global navigation satellite system. [14]
818	Impulse	See pulse. [14]
819	Isobath	See depth curve, fathom line. [14]
820	Rafting	Pressure process whereby one piece of ice overrides another. Most common in new and young ice. [14]
821	Seaweed	Any macroscopic marine alga or seagrass. [14]
822	Sunspot	Any of the dark spots sometimes seen at the surface of the sun; they are believed to have some connection with magnetic disturbances on earth. [14]
823	Terrace	A relatively flat horizontal or gently inclined surface, sometimes long and narrow, which is bounded by a steeper ascending slope on one side and by a steeper descending slope on the opposite side. [14]
824	Tropics	See torrid zone. [14]
825	Abscissa	See coordinates: plane rectangular. [14]
826	Achromat	See achromatic lens. [14]
827	Acid Fog	Cloud droplets or raindrops combining with gaseous pollutants, such as oxides of sulfur and nitrogen, to make falling rain (or snow) acidic pH less than 5.0. If fog droplets combine with such pollutants, it becomes acid fog. [1]
828	Anaglyph	A stereogram in which the two views are printed or projected superimposed in complementary colors, usually red and green. By viewing through filter spectacles of corresponding complementary colors a stereoscopic image is formed. [14]
829	Analogue	The way of representing information by continuous data. [14]
830	Aphelion	That orbital point farthest from the sun when the sun is the center of attraction, as opposed to perihelion. [14]
831	Backrush	The seaward return of water following uprush of waves on a beach. [14]
832	Binnacle	The stand in which a compass is mounted and in which lighting and compensatory units are carried. [14]
833	Bulkhead	On land, a structure or partition built to retain or prevent sliding of the land. A secondary purpose is to protect the upland against damage from wave action. Bulkheads are frequently backfilled thereby increasing the utility of the adjacent land area. [14]
834	Catenary	The curve formed by a uniform cable, chain, or tape supported only at its ends. [14]
835	Chartlet	A small auxiliary chart giving new details on a particular area, to be added to the chart after publication. Also, called block correction or chart amendment patch. A small chart, such as one showing the coverage area of electronic navigational systems, with the distribution of its lines of position, corrections to be applied to readings, location and identification of transmitters, etc. [14]
836	Detritus	In geology, material removed by disintegration and other processes from the surface of rocks. There is a general tendence to use debris. In marine biology, suspended matter of organic origin permanently incapable of reproduction organic detritus may often 'collect' a considerable amount of inorganic material. [14]
837	Downwind	(Adj. And adv.). In the direction toward which the wind is blowing. The opposite is upwind. [14]
838	Drafting	The art of drawing from given specifications. [14]
839	Gridiron	See careening grid. [14]
840	Hardware	All physical material components of a computer system as e.g. Central processing unit (cpu), peripheral devices etc. May also include individual chips. [14]
841	Ice Cake	A floe smaller than 10 m across. If less than 2 m, it is termed brash ice or small ice cake. [14]
842	Ice Rise	A mass of ice resting on rock and surrounded either by an ice shelf or partly by an ice shelf and partly by sea. No rock is exposed and there may be none above sea level. Ice rises often have a dome-shaped surface. The largest known is about 100 km across. [14]
843	Ice Wall	An ice cliff forming the seaward margin of an inland ice sheet, ice piedmont or ice rise. The rock basement may be at or below sea level. See ice front. [14]
844	Landmark	Any fixed object used to mark a boundary on the ground. - 2. Any prominent object at a fixed location on land which can be used in determining a location or a direction. [14]
845	Leadsman	A person using a sounding lead to determine depth of water. [14]
846	Mangrove	One of several genera of tropical trees or shrubs which produce many prop roots and grow along low-lying coasts into shallow water. [14]
847	Mean Sun	See sun. [14]
848	Midnight	Twelve hours from noon, or the instant the time reference crosses the lower branch of the refe-rence celestial meridian. [14]
849	Plankton	The passively drifting or weakly swimming organisms in marine and fresh waters. [14]
850	Scanning	Directing a beam of radiant energy successively over all points of a given region. [14]
851	Seaboard	A general term for the rather extensive coastal region bordering the sea. [14]
852	Sky Wave	See wave. [14]
853	Surveyor	A person engaged in surveying. [14]
854	Taffrail	The after rail at the stern of a vessel. [14]
855	Upstream	(Adj. & adv.). Toward the source of a stream. The opposite is downstream. [14]
856	Waterway	A line of water (river, channel, etc.) Which can be utilized for communication or transport. [14]
857	Wreckage	Goods or parts of a wrecked vessel washed ashore or afloat; remains of a wreck. [14]
858	Anthelion	Pure white, rounded spot, but sometimes iridescent or surrounded by coloured rings or arcs, which appears on very rare occasions opposite the sun and at the same height above the horizon. [14]
859	Backsight	In nautical astronomy, an observation of a celestial body made by facing 180° from the azimuth of the body. In levelling, a reading on a levelling rod held on a point whose elevation has been previously determined and which is not the closing sight of a level circuit. Also written as two words. See also foresight. [14]
860	Civil Day	See day. [14]
861	Data Base	An organized collection of data stored so as to be capable of use by relevant applications with the data being accessed by different logical paths. It should be application independent. [14]
862	Engraving	The act, process or art of cutting or etching designs or letters on metal plates, wooden blocks, etc. For printing. Any printed impression made from an engraved surface. [14]
863	Footscrew	See levelling screw. [14]
864	Free Wave	See wave. [14]
865	Index Arm	A slender bar carrying an index; particularly that bar which pivots at the center of curvature of the arc of a marine sextant and carries the index and the vernier or micrometer. Also called index bar. [14]
866	Isoclinal	N.). See isoclinal line. [14]
867	Isopycnic	(Adj.). Of or pertaining to equal density. [14]
868	Isopycnic	(n.). See isopycnic line. [14]
869	Landspout	Relatively weak non supercell tornado that originates with a cumuliform cloud in its growth stage and with a cloud that does not contain a mid-level mesocyclone. Its spin originates near the surface. Landspouts often look like waterspouts over land. [1]
870	Level Ice	Sea ice with a flat surface which has never been hummocked. [14]
871	Limestone	A rock which consists chiefly of calcium carbonate. [14]
872	Neap Rise	See mean neap rise. [14]
873	Oil Field	An area in which oil occurs in quantities worthy of exploitation. [14]
874	Planetary	(Adj.). Of a planet or the planets. Like a planet. Terrestrial. [14]
875	Polar Ice	Sea ice that is more than one year old (in contrast to winter ice). The WMO code defines polar ice as any sea ice more than one year old and more than 3 meters thick. [14]
876	Pollution	The direct or indirect alteration of the physical, chemical, thermal, biological or radioactive properties of any part of the environment in such a way as to create a hazard or potential hazard to the health, safety or welfare of any living species. [14]
877	Reservoir	A place where anything is collected and stored, generally in large quantity; especially a pond, lake or basin, either natural or artificial, for the storage, regulation and control of water. [14]
878	Responsor	A radio receiver which receives a reply from a transponder and produces an output suitable for feeding to a display system. A responsor is usually combined in a single unit with an interrogator which sends out the pulse that triggers a transponder, the combined unit being called an inter-rogator-responsor. [14]
879	Surf Zone	The area between the outermost breaker and the limit of wave uprush. [14]
880	Tide Wave	A long-period wave associated with the tide-producing forces of the moon and sun; identified with the rising and falling of the tide. Also called tide bulge. See tide, tidal movement, stand of tide. [14]
881	Titration	A chemical method for determining the concentration of a substance in solution. In oceanography, the most common titration is that for chlorinity. [14]
882	Upwelling	The process by which water rises from a lower to a higher depth, usually as a result of divergence and offshore currents. See sinking. [14]
883	Wind Wave	See wave. [14]
884	Young Ice	Newly formed level ice in the transition stage of development from ice rind or pancake ice to winter ice. Thickness from 5 to 15 cm. [14]
885	Anemograph	An instrument which records wind speed and direction. See also anemometer. [14]
886	Bathymetry	The determination of ocean depths. The general configuration of sea floor as determined by profile analysis of depth data. [14]
887	Chlorinity	The total amount in grams of chlorine, bromine and iodine contained in one kilogram of sea water, assuming that the bromine and the iodine had been replaced by chlorine. See salinity. [14]
888	Day: Solar	The duration of one rotation of the earth on its axis, with respect to the sun. This may be either a mean solar day, or an apparent solar day, as the reference is the mean or apparent sun, respectively. The duration of one apparent rotation of the sun. [14]
889	Divergence	In oceanography, a horizontal flow of water, in different directions, from a common center or zone; often associated with upwelling. [14]
890	Driver Rod	A device employed together with a sinker to obtain bottom samples when wire sounding. It consists, essentially, of a galvanized iron tube the lower part of which contains a flap valve for retaining a bottom specimen. The tube releases the sinker when it strikes the bottom. Also called driver tube. [14]
891	Field Stop	The physical element (such as an aperture stop, diaphragm or lens periphery) of an optical system which limits the field of view covered by the system. [14]
892	Gust Front	A boundary that separates a cold downdraft of a thunderstorm from warm, humid surface air. On the surface its passage resembles that of a cold front. [1]
893	Gyro: Free	A two-degree-of-freedom gyro or a gyro the spin axis of which may be oriented in any specified attitude. Also called free gyroscope. [14]
894	Ice Island	A form of tabular berg found in the arctic ocean, with a thickness of 30 to 50 m and from a few thousand square meters to 500 sq. Km in area. Ice islands are characterized by a regularly undulating surface, which gives them a ribbed appearance from the air. [14]
895	Index Mark	In photogrammetry, a real mark (such as a cross or dot) lying in the plane or the object space of a photograph and used singly as a reference mark in certain types of monocular instruments, or as one of a pair to form a floating mark (as in certain types of stereoscopes). [14]
896	Inmarsat-C	The digital satellite communications system for store-and-forward text or data messaging using mobile terminals with omni-directional antennas. Inmarsat-c is the only system (2011) that allows ships to meet the majority of the satellite communication requirements of the gmdss including distress alerting, reception of maritime safety information and general communications. [14]
897	Light List	See list of lights. [14]
898	Lighthouse	A distinctive structure on or off a coast exhibiting a major light designed to serve as an aid to navigation. [14]
899	On The Bow	Bearing approximately 045° relative (on the starboard bow) or 315° relative (on the port bow). The expression is often used loosely for broad on the bow, or bearing exactly 045° or 315° relative. See also broad on the bow. [14]
900	Perihelion	That orbital point nearest the sun, when the sun is the center of attraction, as opposed to aphelion. [14]
901	Rain Gauge	see gauge. [14]
902	Rock Awash	A rock awash at chart datum. [14]
903	Roundabout	A routing measure comprising a separation point or circular separation zone and a circular traffic lane within defined limits. Traffic within the roundabout is separated by moving in a counter-clockwise direction around the separation point or zone. [14]
904	Sea Breeze	A coastal local wind that blows from the ocean onto the land. The leading edge of the breeze is termed a sea-breeze front. [1]
905	Streamline	A line of flow. In meteorology, line envelope in space of the tangents to the instantaneous wind directions at a given time. Also written as two words. See also trajectory. [14]
906	Tidal Wave	See wave. [14]
907	Tide Cycle	See tidal cycle. [14]
908	Tide Range	See range of tide. [14]
909	Tide Staff	A tide gauge consisting of a vertical graduated pole from which the height of tide at any time can be read directly. Also called tide pole. [14]
910	Time: Mean	See time: mean solar. [14]
911	Tropopause	Upper limit of the troposphere. [14]
912	Ultrasonic	(Adj.). Having a frequency above the audible range. [14]
913	Undulating	(Adj.). Having the form of waves or swells, as undulating land. [14]
914	Undulation	A continuously propagated motion to and from, in any fluid or elastic medium, with no permanent translation of the particles themselves. [14]
915	Wave Train	A series of waves moving in the same direction. See wave: solitary. [14]
916	Wind Force	Number on a progressive scale (beaufort wind scale) corresponding to the effects produced by winds within a range of speeds. Force exerted by the wind on a construction, object, etc. [14]
917	Wind Shear	The rate of change of wind speed or wind direction over a given distance. [1]
918	Y-Parallax	See parallax. [14]
919	Archipelago	A group of islands. [14]
920	Circumpolar	(Adj.). Revolving about the elevated pole without setting. A celestial body is circumpolar when its polar distance is approximately equal to or less than the latitude of the observer. The actual limit is extended somewhat by the combined effect of refraction, semidiameter, parallax, and the height of the observer's eye above the horizon. [14]
921	Coastlining	The process of obtaining data from which the coastline can be drawn on a chart. [14]
922	Course Line	A line of position approximately parallel to the course. [14]
923	Danger Area	An area designated by a proper authority, in which a danger to craft exists. Also called danger zone. [14]
924	Datum Level	See datum: vertical control and datum: chart. [14]
925	Dumpy Level	See levelling instrument: dumpy level. [14]
926	Ebb Current	See ebb stream. [14]
927	Equinoctial	See equator: celestial. [14]
928	Gauge: Tide	A device for measuring the height of tide. A graduated staff in a sheltered area where visual observations can be made; or it may consist of an elaborate recording instrument making a continuous graphic record of tide height against time. Such an instrument is usually actuated by a float in a pipe communicating with the sea through a small hole which filters out shorter waves. [14]
929	Ground Wave	See wave. [14]
930	Index Error	See error. [14]
931	Lithography	The art or process of printing from a flat stone or metal plate by a method based on the repulsion between grease and water. The original lithographic material was bavarian limestone; but zinc and aluminium are now used. [14]
932	Median Line	A line every point of which is equidistant from the nearest points on the baselines of two or more states between which it lies. [14]
933	Mesocyclone	A vertical column of cyclonically rotating air within a supercell thunderstorm. [1]
934	On The Beam	Bearing approximately 090° relative (on the starboard beam) or 270° relative (on the port beam). The expression is often used loosely for broad on the beam, or bearing exactly 090° or 270° relative. Also called abeam. See also broad on the beam. [14]
935	Outer Limit	The extent to which a coastal state claims or may claim a specific jurisdiction in accordance with the provisions of international law. [14]
936	Phase Angle	The phase difference of two periodically recurring phenomena of the same frequency, expressed in angular measure. The angle at a celestial body between the sun and earth. [14]
937	Polar Front	Quasi-permanent front of great extent, of middle latitudes, which separates relatively cold polar air and relatively warm tropical air, and on which waves are produced. [14]
938	Rising Tide	See tide. [14]
939	Sedimentary	(Adj.). Formed by the deposition of sediment. [14]
940	Signal Lamp	See lamp. [14]
941	Slant Range	See slant distance. [14]
942	Spring Rise	See mean spring rise. [14]
943	Stereoscope	A binocular optical instrument for helping an observer to view photographs, or diagrams, to obtain the mental impression of a three-dimensional model. [14]
944	Stereoscopy	The science and art which deals with the use of binocular vision for observation of a pair of overlapping photographs or other perspective views, and with the methods by which such viewing is produced. [14]
945	Tidal Range	See range of tide. [14]
946	Projection: Transverse Mercator	A projection of the cylindrical type, being in principle equivalent to the regular Mercator projection turned (transverse) 90° in azimuth. In this projection, the central meridian is represented by a straight line, corresponding to the line which represents the equator on the regular Mercator projection. Neither the geographical meridians, except the central meridian, nor the geodetic paral-lels, except the equator (if shown), are represented by straight lines. It is a conformal projection. Also called transverse cylindrical orthomorphic projection. [14]
947	Bog	Wet spongy ground consisting of decaying vegetation, which retains stagnant water, too soft to bear the weight of any heavy body. [14]
948	MWL	Mean water level (MWL) ; The average of all hourly water levels over the available period of record. [12]
949	Beat	The periodic variation that results from the superposition of two oscillations whose frequencies differ by a small amount. [14]
950	Coma	An aberration affecting the sharpness of images off the axis, in which rays from a point object off the axis passing through a given circular zone of the lens, come to a focus in a circle rather than a point, and the circles formed by rays through different zones are of different sizes and are located at different distances from the axis. Therefore, the image of a point object is comet-shaped. The foggy envelope surrounding the nucleus of a comet. [14]
951	Crab	The condition caused by failure to orient a camera with respect to the track of the airplane. In vertical photography, crab is indicated by the edges of the photographs not being parallel to the airbase lines. [14]
952	Dgps	See differential gps [14]
953	Dune	A mound, ridge or hill of drifted sand on the seacoast or in a desert. See sand dune and down. [14]
954	Gale	Wind with a speed between 32 and 37 knots (beaufort scale wind force 8). [14]
955	Gnss	See global navigation satellite system [14]
956	Grab	A kind of closing scoop or bucket used in dredging or for bringing up bottom samples. [14]
957	HHWL	Highest High Water Level (HHWL) [-]
958	Hook	A sharp bend or angle in the course or length of anything; especially a bend in a river. A projecting corner, point or spit of land. [14]
959	LLWL	Lower Low Water Line (LLWL) ; The intersection of the land (shore) with the water surface at the elevation of mean lower low water. [23]
960	Loch	The Scottish term for (1) a lake, and (2) a fiord. [14]
961	Marl	A crumbling, earthy deposit, particularly one of clay mixed with sand, lime, decomposed shells, etc. Sometimes a layer of marl becomes quite compact. Part of the ocean bed is composed of marl. [14]
962	Mesa	A high tableland (s.w. And w. United states). [14]
963	MHWL	Mean High Water Line (MHWL); The line on a chart or map which represents the intersection of the land with the water surface at the elevation of mean high water. [22]
964	Mire	A piece of wet swampy ground. [14]
965	MLWL	Mean Low Water Line (MLWL); The intersection of the land (shore) with the water surface at the elevation of water level. [23]
966	Neck	In oceanography, the narrow band of water flowing swiftly seaward through the surf. See current: rip. In geography, a narrow piece of land with water on each side; an isthmus. [14]
967	Ramp	A sloping structure that can either be used, as a landing place, at variable water levels, for small vessels, landing ships, or a ferry boat, or for hauling a cradle carrying a vessel. An accumulation of snow that forms an inclined plane between land or land ice elements and sea ice or ice shelf. Also called drift ice foot. [14]
968	Sbes	See single beam echo sounder [14]
969	Spur	A subordinate elevation, ridge or rise projecting outward from a larger feature. [14]
970	Vein	A narrow lead or lane in pack ice. In mineralogy, a crack or fissure in the rocks of the earth's crust in which highly heated waters from below have deposited from solution crystalline minerals (especially vein quartz) and, under certain circumstances, metallic minerals of economic importance. [14]
971	Volt	The unit of potential difference or electromotive force in the si system. [14]
972	Weir	A dam erected across a river to raise the level of the water. A fence of stakes set in a river or along the shore as a trap for fish. The word is now restricted to smaller works, the larger are called dams. [14]
973	Zoom	A method of enlarging graphics on a graphical display, usually a function provided by the hardware of the screen. Either a selected window may be enlarged to cover the entire screen or by repeatedly pressing a key, a stepwise or continuous enlargement of the screen contents can be invoked, keeping the graphics centered at the screen's center. [14]
974	Atlas	A collection of charts or maps to be kept (loose or bound) in a volume. [14]
975	Atoll	A coral island consisting of a ring-shaped reef nearly or entirely surrounding a central lagoon. [14]
976	Bayou	A minor sluggish waterway or estuarial creek, generally tidal or characterized by a slow current, with a course generally through lowlands or swamps, tributary to or connecting with other bodies of water. Various specific meanings have been implied in different parts of the southern united states. Sometimes called slough. [14]
977	Bench	See terrace. [14]
978	Clean	(Adj.). Free from obstructions, unevenness, imperfections, as a clean anchorage. [14]
979	Fucus	See rockweed. [14]
980	Gorge	A narrow opening, between hills, usually with precipitous sides. [14]
981	Guyot	See table mount. [14]
982	Halos	Rings or arcs that encircle the sun or moon when seen through an ice crystal cloud or a sky filled with falling ice crystals. Halos are produced by refraction of light. [1]
983	Joule	The unit of work or energy in the si system. [14]
984	Lagan	See jettison. [14]
985	Panel	In cartography, the completed assembly of pieces of film positives onto a grid or projection which is used as a base for compilation. In photogrammetry, an element of a target used for control station identification on aerial photography. [14]
986	Perch	A staff placed on top of a buoy, rock, or shoal as a mark for navigators. A ball or cage is sometimes placed at the top of the perch, as an identifying mark. A unit of length equal to 5.5 yards or 16.5 feet. Also called rod, pole. [14]
987	Pingo	Small conical hills having a large central core of ice formed from the encroachment of permafrost and the resulting hydrostatic pressure. [14]
988	Saros	The eclipse cycle of about 18 years, almost the same length as 223 synodical months. At the end of each saros the sun, moon, and line of nodes return to approximately the same relative positions, and another series of eclipses begins, closely resembling the series just completed. [14]
989	Scour	The action of a current or flow of water in clearing away mud or other deposit; in civil engineering an artificial current or flow produced for this purpose. [14]
990	Shoot	(v.t.). To observe the altitude of (a celestial body). [14]
991	Spray	Ensemble of water droplets torn by the wind from the surface of an extensive body of water, gene-rally from the crests of waves, and carried up a short distance into the air. [14]
992	Tyfon	See typhon. [14]
993	Vigia	A pinnacle, rock, or shoal the existence or position of which is doubtful, or a warning note to this effect on a chart. [14]
994	Wrack	See rockweed. [14]
995	Albedo	The ratio of radiant energy reflected to that received by a surface, usually expressed as a percentage. [14]
996	Ampere	The unit of density of electric current in the si system. [14]
997	Boomer	Seismic instrument for shallow penetration work. The boomer transducer produces acoustic pulses by the motion of a metal plate in the water. [14]
998	Cirrus	A high cloud composed of ice crystals in the form of thin, white, featherlike clouds in patches, filaments, or narrow bands. [1]
999	Defile	A narrow pass or gorge between mountains. [14]
1000	F-Stop	See aperture: relative. [14]
1001	Furrow	On the sea floor, a closed, linear, narrow, shallow depression. [14]
1002	Gravel	Loose detrital material ranging in size from 2 to 256 mm. [14]
1003	Intake	The place where water is taken into a channel or pipe from a river or other body of water, to drive a mill, or supply a canal, waterworks, etc. [14]
1004	Jetsam	See jettison. [14]
1005	Leaper	See lipper. [14]
1006	Mantle	The relatively plastic region between the crust and core of the earth. Also called asthenosphere. [14]
1007	Micron	One millionth of a metre; one thousandth of a millimeter. [14]
1008	Navtex	The system for the broadcast and automatic reception of maritime safety information by means of narrow-band direct-printing telegraphy. [14]
1009	Neaped	See beneaped. [14]
1010	Nekton	Those animals of the pelagic division that are active swimmers, such as most of the adult squids, fishes, and marine mammals. [14]
1011	Nexrad	An acronym for next generation weather radar. The main component of nexrad is the wsr 88-d, doppler radar. [1]
1012	Octant	A double-reflecting instrument for measuring angles. It is similar to a sextant but has an arc of only 45°. [14]
1013	Pebble	A small stone worn smooth and rounded by the action of water, sand, ice, etc. Ranging in diameter between 4 and 64 millimeters. [14]
1014	Pinger	A battery powered acoustic device equipped with a transducer that transmits sound waves. When the pinger is attached to a wire and lowered into the water, the direct and bottom reflected sound can be monitored with a listening device. The difference between the arrival time of the direct and reflected waves is used to compute the distance of the pinger from the ocean bottom. [14]
1015	Saddle	A broad pass or col, resembling in shape a riding saddle in a ridge or between contiguous elevations. [14]
1016	Schist	A foliated metamorphic rock which can be split into thin flakes or flat lenticles. Schists are usually named from the dominant mineral, e.g. Mica schist. [14]
1017	Scoria	(pl. Scoriae). Volcanic rock fragments usually of basic composition, characterized by marked vascularity, dark colour, high density, and a partly crystalline texture. [14]
1018	Seiche	A standing wave oscillation of an enclosed or semi-enclosed water body that continues, pendulum fashion, after the cessation of the originating force, which may have been either seismic, atmospheric, or wave induced. [14]
1019	Strays	In echo sounding, false indications occasionally appearing on the dial or fathogram of an echo sounder. They may be caused by the motion of the vessel through the water, by acoustic or electric noises in the ship, or by electric noises in the echo sounding equipment. Strays may be mistaken for the true echo or may be of such a nature as to prevent the identification of the true echo. [14]
1020	Sunset	The crossing of the apparent horizon by the upper limb of the descending sun. [14]
1021	Syzygy	In astronomy, either of two opposing points in the orbit of a planet or satellite, especially of the moon, at which it is in conjunction with or in opposition to the sun. [14]
1022	Trench	A long narrow, characteristically very deep and asymmetrical depression of the sea floor with relatively steep sides. [14]
1023	Upland	The higher ground of a region contrasted with the valleys and plains. Used in contrast to lowland. [14]
1024	Upwind	(Adj. & adv.). In the direction from which the wind is blowing. The opposite is downwind. [14]
1025	Window	In computer applications, a rectangular subdivision of the screen showing information without affec-ting other parts of the screen; a method allowing to view different items of information (e.g. Different data sets or graphics) at the same time. On graphical displays a window may be selected with the cursor and subsequently be enlarged (zoom). [14]
1026	X-Axis	A horizontal axis in a system of rectangular coordinates; that line on which distances to the right or left (east or west) of the reference line are marked, especially on a map, chart, or graph. [14]
1027	Benthos	The category of marine organisms that live on, in, or close to the bottom of the oceans. [14]
1028	Bollard	Small, shaped post, mounted on a wharf or dolphin used to secure ship's lines. Also see mooring. [14]
1029	Ceiling	See height of cloud base. [14]
1030	Cinders	Fragments formed when magma is blown into the air; larger in size than volcanic ash. Cinders are a constituent of certain marine sediments. [14]
1031	Easting	The distance a craft makes good to the east. The opposite is westing. In a cartesian reference system the value of one coordinate, usually expressed in meters, measured from the central meridian in east-west direction; used e.g. In the UTM system. [14]
1032	Ecology	The science of the economy of animals and plants dealing with the relations of living organism to their surroundings. [14]
1033	Estuary	That portion of a stream influenced by the tide of the body of water into which it flows. A bay, as the mouth of a river, where the tide meets the river current. [14]
1034	Eyewall	A wall of dense thunderstorms that surrounds the eye of a hurricane. [1]
1035	Flotsam	See jettison. [14]
1036	Fouling	The mass of living and non-living bodies and particles attached to or lying on the surface of a submerged man-made or introduced object; more commonly considered to be only the living or attached bodies. [14]
1037	Gibbous	Adj.). See phases of the moon. [14]
1038	Headway	Motion in a forward direction. Also called seaway. [14]
1039	Hillock	A small hill. [14]
1040	Ice Age	The most recent period of extensive continental glaciation that saw large portions of north America and Europe covered with ice. It began about 2 million years ago and ended about 10,000 years ago. See pleistocene epoch. [1]
1041	Ice Fog	See fog. [14]
1042	Icefoot	A narrow strip of ice attached to the coast, unmoved by tides and remaining after the fast ice has broken free. [14]
1043	Imagery	Techniques to obtain, process or interpret images created by different types of radiation, e.g. Light, infrared, x-rays. [14]
1044	Insular	Of or pertaining to an island or islands. [14]
1045	Isogram	That line on a chart or diagram connecting points having equal values of same phenomenon. [14]
1046	Isoline	A line representing the intersection of the plane of a vertical photograph with the plane of an overlapping oblique photograph. If the vertical photograph were tilt-free, the isoline would be the isometric parallel of the oblique photograph. [14]
1047	Moonbow	Rainbow whose formation is the same as that of the ordinary rainbow, but whose light comes from the moon and not from the sun. Also called lunar rainbow. [14]
1048	New Ice	A general term which includes frazil ice, slush, sludge, pancake ice and ice rind. [14]
1049	Overlay	In mapping, a record on a transparent medium to be superimposed on another record. [14]
1050	Polygon	A non-self-intersecting, closed chain defining the boundary of an area. [14]
1051	Polynia	A water area enclosed in ice, generally fast; this water area remains constant and usually has an oblong shape; sometimes limited to one side by the coast. Any enclosed sea water area in pack ice other than a lead, not large enough to be called open water. If a polynia is found in the same region every year, for example, off the mouths of big rivers, it is called a recurring polynia. A temporary small clearing in pack ice which consists of small ice floes and brash ice in continuous local movement is called an unstable polynia; an opening which is flanked by large floes and therefore appears to be relatively stable is called a stable polynia. When frozen over, a polynia becomes an ice skylight from the point of view of the submariner. [14]
1052	Rip-Rap	See groin. [14]
1053	Scanner	A device for directing a beam of radiant energy successively over all points of a given region. In data processing a photo-electronic device for digital reproduction of pictures. The picture is scanned line wise and decomposed into a matrix-like raster of individual pixels. In contrast to vectorial digitizers, the information to coherent elements of the picture (lines, symbols) is lost by this rasterization process. To retrieve these elements the rasterized picture has to be vectorized by pattern recognition methods and manual post-processing. [14]
1054	Slipway	The prepared and usually reinforced inclined surface on which keel- and bilge-blocks are laid for supporting a vessel under construction. [14]
1055	Spicule	A minute needlelike or multiradiate calcareous or siliceous body in sponges, radiolarians, primitive chitons, and echinoderms. They frequently are identified in marine sediment samples. [14]
1056	Stratus	A low, gray cloud layer with a rather uniform base whose precipitation is most commonly drizzle. [1]
1057	Sunrise	The crossing of the apparent horizon by the upper limb of the ascending sun. [14]
1058	Swinger	See fix: circular. [14]
1059	Tagline	A line, either marked at equal intervals or run over a registered sheave, used in large-scale surveys to take equally spaced soundings at predetermined distances from the control stations. [14]
1060	Tie Net	See triangulation net. [14]
1061	Topmark	A characteristic shape secured at the top of a buoy or beacon to aid in its identification. [14]
1062	Torrent	Rushing stream of water; great downpour of rain. [14]
1063	Typhoon	Name given to tropical cyclones of the china sea and, more generally, of the north-west pacific. [14]
1064	Variate	A variate is a quantity that may take on any of the values of a specified set with a specified relative frequency or probability often known as random variable. It is to be regarded as defined not merely by a set of permissible values, but by an associated frequency (probability) function expressing how often those values appear in a given situation. [14]
1065	Abrasion	The wearing away or rounding of surfaces by friction. [14]
1066	Aeronomy	Term proposed for the study of the chemistry and physics of the high atmosphere. [14]
1067	Aliasing	An occurrence in tidal analysis when the sea level varies with a period that is less than the sampling period. Due to the varying position of the samples on the curve, a spurious tidal frequency appears in the analysis. It is usually only possible when there is a seiche at the observation site or observations are taken at intervals greater than one hour. [14]
1068	Base Net	See base extension triangulation. [14]
1069	Bow Echo	A line of thunderstorms on a radar screen that appears in the shape of a bow. Bow echoes are often associated with damaging straight-line winds and small tornadoes. [1]
1070	Bridging	See stereo triangulation. [14]
1071	Can Buoy	A buoy the above-water part of which is in the shape of a cylinder. Sometimes called cylindrical buoy. [14]
1072	C-Factor	(US Terminology). In photogrammetry, an empirical value which expresses the vertical measuring capability of a given stereoscopic system; generally defined as the ratio of the flight height to the smallest contour interval accurately plottable. The c-factor is not a fixed constant but varies over a considerable range, according to the elements and conditions of the photogrammetric system. In planning for aerial photography, the c-factor is used to determine the flight height required for a specified contour interval, camera, and instrument system. [14]
1073	Clearing	See clearance. [14]
1074	Compiler	A program that translates programs from one programming language (source program) into another programming language (object program). Typically, the compiler translates from a higher, user understandable language to a lower, machine interpretable language. [14]
1075	Crescent	Adj.). See phases of the moon. [14]
1076	Dan Buoy	A buoy consisting of a ballasted float carrying a staff which supports a flag or light. [14]
1077	Derelict	Any property abandoned at sea, often of sufficient size as to constitute a menace to navigation, especially an abandoned vessel. See wreck. [14]
1078	Ebb Tide	See tide: falling. [14]
1079	Echogram	A graphic record of depth measurements obtained by an echo sounder. See fathogram. [14]
1080	Eelgrass	See seagrass. [14]
1081	Epipoles	In the perspective set-up of two photographs, (two perspective projections), the points on the planes of the photographs where they are cut by the air base. [14]
1082	Evection	A perturbation of the moon in its orbit due to the attraction of the sun. See also lunar inequality. [14]
1083	Eye Base	See interpupillary distance. [14]
1084	F-Number	See aperture: relative. [14]
1085	Gustnado	A relatively weak tornado associated with a thunderstorm's outflow. It most often forms along the gust front. [1]
1086	Hachures	Short lines drawn on a chart or map for representing relief. These lines are drawn in the direction of the slope and intensified on the shaded side of the feature assuming the area is illuminated from the north-west. Unlike the contour lines, they give no indication of the actual height of land above sea level. See also hill shading. [14]
1087	Headland	A high steep promontory. Usually called head when coupled with a specific name. [14]
1088	Ice Floe	See floe. [14]
1089	Ice Rind	A thin, elastic, shining crust of ice, formed by the freezing of sludge on a quiet sea surface. Thickness less than 5 cm. [14]
1090	Icebound	(Adj.). Said of a harbor, inlet, etc. When navigation by ships is prevented due to ice, except possibly with the assistance of an icebreaker. Of a ship, surrounded so closely by ice as to be incapable of proceeding. [14]
1091	Isopleth	An isogram of equal or constant value of a given quantity, with respect to either time or space. [14]
1092	Isotherm	In meteorology, the line which is the locus of points which have the same value of air temperature. [14]
1093	Jettison	The throwing overboard of objects, especially to lighten a craft in distress. Jettisoned objects that float are termed flotsam; those that sink, jetsam; and heavy articles that are buoyed for future recovery, lagan. See derelict. [14]
1094	Landfall	The first sighting of land when approached from seaward. By extension, the term is sometimes used to refer to the first contact with land by any means, as by radar. [14]
1095	Layering	A method of emphasizing on a chart differences in height or depth by use of varying tints. Also referred to as layer tinting. [14]
1096	Log Chip	The wooden quadrant forming part of a chip log. Also called log ship. [14]
1097	Lunation	See month: synodical. [14]
1098	Mainland	The principal land or largest part of a continent, as distinguished from a relatively small island or peninsula. [14]
1099	Marigram	See tide curve. [14]
1100	Masthead	The top of a mast. [14]
1101	Northing	The distance a craft makes good to the north. The opposite is southing. In a cartesian reference system the value of one coordinate, usually expressed in meters, measured from the origin in north-south direction; used e.g. In the UTM system. [14]
1102	Nutation	Irregularities in the precessional motion of the equinoxes because of varying positions of the moon, and, to a lesser extent, of other celestial bodies, with respect to the ecliptic. Because of nutation the earth's axis nods like a top, describing an irregular circle about the mean pole in a period of about 19 years. [14]
1103	Odograph	A mechanical instrument containing a distance-measuring element which is moved or turned by an amount proportional to the actual distance travelled; a compass element which provides a fixed-reference direction, and an integrator which provides for the resolution of the direction of motion into components and for the summation or integration of the distance components. Also, an instrument for recording the distance travelled by a vehicle or pedestrian. [14]
1104	Overtide	A shallow water harmonic tide constituent with a speed that is a multiple of the speed of one of the basic constituents of the tide-producing force. See harmonic constituent, and shallow water constituent. [14]
1105	Photomap	A photomosaic of a specified land area, which also contains marginal information, descriptive data, and a reference grid and/or projection. See also mosaic. [14]
1106	Piedmont	(Adj.). Situated or formed at the base of mountains. [14]
1107	Pigments	A colouring matter used as paint or dye or a natural colouring matter of a tissue. [14]
1108	Province	In oceanography and in a morphological sense, a region composed of a group of similar physiographic features whose characteristics are markedly in contrast with surrounding areas (rarely used in marine cartography). [14]
1109	Red Tide	A red or reddish-brown discoloration of surface waters, most frequently in coastal regions, caused by concentration of certain microscopic organisms, particularly dinoflagellates. Toxins produced by the dinoflagellates can cause mass kills of fishes and other marine animals. [14]
1110	Revolver	See fix: circular. [14]
1111	Sea Buoy	See farewell buoy. [14]
1112	Sea Mile	The length of one minute of arc, measured along the meridian in the latitude of the position; its length varies both with the latitude and with the figure of the earth in use. Used in navigation to measure distances on sea charts using the Mercator projection. Not to be confused with nautical mile or international nautical mile. [14]
1113	Sea Wall	An embankment or wall for protection against waves or tidal action along a shore or water front. [14]
1114	Seagrass	Any grass like marine alga. Eelgrass is one of the best known seagrasses. [14]
1115	Shallows	An indefinite term applied to expanses of shoal or shallow water. [14]
1116	Stellite	A trade name for an alloy of chromium, cobalt and tungsten. Stellate mirrors, free of imperfection and practically indestructible, are frequently used in hydrographic sextants. See sextant: sounding. [14]
1117	Stranded	(1) the terms "stranded" and "sunken" apply exclusively to items that once were afloat but which are now resting on the bottom. Stranded items project above the sounding datum while sunken items do not project above the sounding datum. These terms apply most often to wrecks. Masts, funnels, and other extensions of wreck superstructure should be disregarded when applying the above definition; i.e., such features may project above the sounding datum and still have the wreck classified as sunken. (2) the grounding of a vessel so that it is not soon refloated; a serious grounding. [14]
1118	Tideland	Land which is under water at high tide and uncovered at low tide. [14]
1119	Time Tag	Reference assigned to each measurement input from a sensor to identify the time (either cpu, gps, or utc) when a measurement was actually made by that particular sensor; time tags allow adjustment of data from different sensors to a common time reference. [14]
1120	True Sun	See sun: apparent. [14]
1121	Waveform	The graphical representation of a wave, showing variation of amplitude with time. Also written as two words. [14]
1122	Wetlands	The term "wetlands" means those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas. [14]
1123	Acclivity	An upward slope of ground; as opposed to declivity. [14]
1124	Acid Rain	Cloud droplets or raindrops combining with gaseous pollutants, such as oxides of sulfur and nitrogen, to make falling rain (or snow) acidic pH less than 5.0. If fog droplets combine with such pollutants it becomes acid fog. [1]
1125	Air Speed	The speed of an aircraft relative to the surrounding atmosphere. As opposed to ground speed. [14]
1126	Backbeach	Also written as two words. See backshore. [14]
1127	Bar Scale	See scale. [14]
1128	Basepoint	A basepoint is any point on a baseline. [14]
1129	Blackbody	A hypothetical object that absorbs all of the radiation that strikes it. It also emits radiation at a maximum rate for its given temperature. [1]
1130	Box Gauge	See gauge: float. [14]
1131	Capacitor	See condenser. [14]
1132	Data Bank	A collection of data in a common location, relating to a given set of subjects. Usually comprised of several data bases considered as an entity. [14]
1133	Daybeacon	An unlighted beacon. A day beacon is identified by its colour, shape, and number of its daymark. The simplest form of day beacon consists of a single pile with a daymark affixed at or near its top. [14]
1134	Decimetre	One-tenth of a metre. [14]
1135	Declivity	A downward slope or sloping of a hill; as opposed to acclivity. [14]
1136	Depth Ice	See anchor ice. [14]
1137	Dock: Dry	An artificial basin fitted with a gate or caisson, into which vessels can be floated and the water pumped out to expose the vessel's bottom. Also called graving dock. [14]
1138	Downburst	A severe localized downdraft that can be experienced beneath a severe thunderstorm. (compare microburst and macroburst.) [1]
1139	Draft Aft	See draft. [14]
1140	Echometer	(France). An ultrasonic echo sounder with a visual depth-indicating device. The signals are produced and received by quartz-crystal transmitting and receiving units. Its range is from 6 to 660 meters. [14]
1141	Echoscope	(France). An ultrasonic echo sounder similar to echometer. The echoscope is portable, intended for shoal-water sounding from small boats. Its range is from 1 to 60 meters. [14]
1142	Facsimile	An exact reproduction or copy. [14]
1143	Fathogram	A graphic record of depth measurements obtained by a fathometer (erroneously applied to any echogram). [14]
1144	Fish Farm	An assemblage of cages, nets, rafts and floats or posts where fish, including shellfish, are artificially cultivated. [14]
1145	Foreshore	That part of shore which lies between high and low water mark at ordinary tide. [14]
1146	Foresight	In levelling, a reading on a levelling rod held on a point whose elevation is to be determined. See also backsight. [14]
1147	Grivation	See variation: grid. [14]
1148	Hailstone	Globule or piece of ice, with a diameter varying between 5 and 50 mm or even more, the fall of which constitutes hail. Hailstones consist almost entirely of transparent ice, or of a series of layers of transparent ice with a thickness of at least 1 mm, alternating with translucent layers. [14]
1149	Half Tide	See tide. [14]
1150	Hard Iron	Iron or steel which is not readily magnetized by induction, but which retains a high percentage of the magnetism acquired. The opposite is soft iron. [14]
1151	High Noon	See noon: local apparent. [14]
1152	Hoarfrost	Deposit of ice, having a crystalline appearance, generally assuming the form of scales, needles, feathers or fans. Hoarfrost is produced in a manner similar to dew but at a temperature below 0°c. Also written as two words. [14]
1153	Hodograph	Used in oceanography. The tidal current vector hodograph is the figure traced out by the tip of a vector representing the current over the tidal cycle. [14]
1154	Hydrology	The scientific study of the waters of the earth, especially with relation to the effects of precipitation and evaporation upon the occurrence and character of water in streams, lakes, and on or below the land surfaces. [14]
1155	Ice Front	The vertical cliff forming the seaward face of an ice shelf. See ice wall. [14]
1156	Ice Shelf	A floating ice sheet of considerable thickness. Ice shelves are usually of great horizontal extent and have a level or gently undulating surface. They are nourished by local snow accumulation and often also by the seaward extension of land glaciers. Limited areas may be aground. The initial stage is called bay ice until the surface is more than about 2 m above sea level. The seaward edge is termed an ice front. [14]
1157	Isometric	(Adj.). Of or pertaining to equal measure. [14]
1158	Jellyfish	Any of various free-swimming coelenterates having a disc- or bell-shaped body of jellylike consistency. Many have long tentacles with nematocysts (stinging cells). Some are capable of producing glowing ball luminescence. Any jellylike free-floating organism. The term 'jellyfish' often is applied to the ctenophores and may be applied to certain tunicates. Also called medusa. [14]
1159	Land Mile	See statute mile. [14]
1160	Lee Shore	Shore that is to leeward of a vessel. See weather shore. [14]
1161	Lens Axis	See axis of lens. [14]
1162	Level Net	Lines of spirit levelling connected together to form a system of loops and circuits extending over an area. Also called survey net. [14]
1163	Limnology	The scientific study of the biological, chemical, geographical, and physical features of fresh waters, especially of lakes and ponds. [14]
1164	Loxodrome	A curve, on the surface of a sphere, intersecting all great circles of the sphere at a constant oblique angle, theoretically never reaching the pole while closely approaching it. See rhumb line. [14]
1165	Lunar Day	See day. [14]
1166	Megahertz	One million hertz; one thousand kilohertz. The term is used as the equivalent of one million cycles per second. [14]
1167	Milky Way	A broad, faintly luminous band seen across the sky at night, consisting of innumerable stars and nebulae, so distant as to be indistinguishable without a telescope. [14]
1168	Nearshore	Close to the shore. [14]
1169	Noctiluca	A genus of usually pale pink luminescent dinoflagellates large enough to be seen by the unaided eye. This particular organism is responsible for much of the sheet-type luminescence noted in coastal waters of various parts of the world ocean. [14]
1170	Occlusion	Process of progressive decrease of area of warm sector at the earth's surface, and its ultimate disappearance, by the junction of the cold air masses which initially precede the warm front and follow the cold front. Front between these two cold air masses, after their junction (also termed occluded front). [14]
1171	Pedometer	A pocket-size instrument which registers in linear units the distance traversed by the pedestrian carrying it. See passometer. [14]
1172	Peninsula	A piece of land that is almost an island, being nearly surrounded by water; by extension any piece of land projecting into the sea, so that the greater part of its boundary is coastline. [14]
1173	Phase Lag	Angular retardation of the maximum of a constituent of the observed tide behind the correspon-ding maximum of the same constituent of the hypothetical equilibrium tide. Also called tidal epoch. [14]
1174	Planetoid	See asteroid. [14]
1175	Processor	See microprocessor. [14]
1176	Range Rod	A simple surveyor's rod, fitted with a sharp-pointed steel shoe. It is usually painted red and white alternately, and used to line up points of a survey. [14]
1177	Reef Flat	A flat expanse of dead reef rock which is partly or entirely dry at low tide. [14]
1178	Remanence	See magnetic retentivity. [14]
1179	Resonance	Re-enforcement or prolongation of any wave motion, such as sound, radio waves, etc., resulting when the natural frequency of the body or system in vibration is equal to that of an impressed vibration. In tides, the water movement resulting from the natural period of oscillation of a body of water which approximates the period of one of the tide-producing forces. [14]
1180	Responder	A transmitter, fitted to a submersible or on the seabed, which can be triggered by a hardwired external control signal to transmit an interrogation signal which is received by a transducer or hydrophone. [14]
1181	Revetment	Facing of stone or other material, either permanent or temporary, placed along the edge of a stream to stabilize the bank and to protect it from the erosive action of the stream. [14]
1182	Sea Reach	The straight part of a river between the last bend and the sea. [14]
1183	Side Shot	A reading or measurement from a survey station to locate a point which is not intended to be used as a base for the extension of the survey. A side shot is usually made for the purpose of determining the position of some object which is to be shown on the map. [14]
1184	Snowstorm	Storm of blowing snow. [14]
1185	Telemeter	An instrument for determining the distance from one point to another. Some such instruments employ a telescope and measure the angle subtended by a short base of known length. The complete equipment for measuring any quantity, transmitting the results electrically to a distance point, and there recording the values measured. [14]
1186	Threshold	In aeronautical terminology, the beginning of that portion of the runway usable for landing. [14]
1187	Tide Lock	A lock situated between a basin or canal and tidewater to maintain the water at a desired level as the height of the tide changes. Also called guard lock. [14]
1188	Tide Pole	See tide staff. [14]
1189	Tidewater	Water affected by tides or sometimes that part of it which covers the tideland. The term is sometimes used broadly to designate the seaboard. See tidal waves. [14]
1190	Timepiece	An instrument for measuring time. See chronometer, clock, watch. [14]
1191	Tributary	A river which joins a larger one. [14]
1192	Tunny Net	A net built at sea for catching tunnies. [14]
1193	Washovers	Small deltas formed on the lagoon side of a bar separating the lagoon from the open sea. Storm waves breaking over the bar deposit sediment on the lagoon side in the form of deltas. Also called wave deltas. [14]
1194	Watershed	Water-parting. The whole region or area contributing to the supply of a river or lake; drainage area; catchment area or basin. [14]
1195	Wind Rose	For a given station and period of time, a star-shaped diagram indicating the relative frequencies of different directions of wind, sometimes also the frequencies of groups of wind speeds in different directions. [14]
1196	Wind Tide	See wind set-up. [14]
1197	Almucantar	Any small circle on the celestial sphere parallel to the horizon. Also called parallel of altitude. [14]
1198	Barysphere	See centrosphere. [14]
1199	Blind Seas	See blind rollers. [14]
1200	Blind Zone	An area within or from which little or no radio signal is received. Also called zone of silence. [14]
1201	Breakwater	A structure protecting a shore area, harbor, anchorage, or basin from waves. See also floating breakwater. [14]
1202	Challenger	See interrogator. [14]
1203	Chromatism	See aberration of light. [14]
1204	Clinometer	An instrument for indicating the degree of slope or the angle of roll or pitch of a vessel, according to the plane in which it is mounted. [14]
1205	Cocked Hat	Triangle on chart, formed by three position lines that do not cross at one point. Also called triangle of error. Note. This expression is seldom used by american navigators. [14]
1206	Compacting	Pieces of sea ice are said to be compacting when they are subjected to a converging motion, which increases ice concentration and/or produces stresses which may result in ice deformations. [14]
1207	Compensate	(v.t.). To counteract an error, as in an instrument; to counterbalance. [14]
1208	Daily Rate	See chronometer rate. [14]
1209	Datum Line	See reference line. [14]
1210	Day Number	The sequentially numbered day of the year, usually starting with day number 1 on 1st January. [14]
1211	Definition	In photography, and electronic equipment, the degree of clarity and sharpness of an image. See resolution and resolving power. [14]
1212	Dove Prism	A prism which reverts the image but does not deviate nor displace the beam. A given angular rotation of the prism about its longitudinal axis causes the image to rotate through twice the angle. Also called a rotating prism. [14]
1213	Downstream	(Adj. and Adv.). In the direction of flow of a current or stream. The opposite is upstream. [14]
1214	Earthshine	See earth light. Also written as two words. [14]
1215	Embankment	An artificial elevation composed of earth, stone, etc. To hold back water. [14]
1216	Escarpment	An elongated, characteristically linear, steep slope, separating horizontal or gently sloping sectors of the sea floor in non-shelf areas. Also abbreviated to scarp. [14]
1217	False Echo	See echo. [14]
1218	Field Work	All activities in the field required for a hydrographic survey. [14]
1219	Flood Tide	See tide: rising. [14]
1220	Frazil Ice	Fine spicules or plates of ice in suspension in water. [14]
1221	Grease Ice	A later stage of freezing than frazil ice when the crystals have coagulated to form a soupy layer on the surface. Grease ice reflects little light, giving the sea a matt appearance. [14]
1222	Hack Watch	See watch. [14]
1223	Heat Burst	A sudden increase in surface air temperature often accompanied by extreme drying. A heat burst is associated with the downdraft of a thunderstorm, or a cluster of thunderstorms. [1]
1224	Heliograph	A device for reflecting the sun's rays from one point to another for sending messages. In meteorology, instrument which records the time interval during which solar radiation reaches sufficient intensity to cast distinct shadows. Also called sunshine recorder. [14]
1225	Heliotrope	See heliostat. [14]
1226	Hygrograph	Hygrometer which includes an arrangement for the time recording of atmosphere humidity. [14]
1227	Hypsograph	A circular instrument of the slide-rule type used to compute elevations from vertical angles and horizontal distances. [14]
1228	Hypsometer	A device for measuring heights of land surfaces by the boiling point of water. [14]
1229	Julian Day	The number of each day, as reckoned consecutively since the beginning of the present Julian period on January 1, 4713 BC. The Julian day begins at noon, 12 hours later than the corresponding civil day. [14]
1230	Landlocked	(Adj.). Almost or quite enclosed by land. Said of an area of water, as a bay, harbor, etc., entirely protected from the sea. [14]
1231	Large Halo	See halo. [14]
1232	Level Axis	See axis of spirit level. [14]
1233	Light Beam	A group of pencils of light, as those originating at the many points of an illuminated surface. A beam of parallel light rays is a special case in which each pencil is of such small cross-section that it may be regarded as a ray. [14]
1234	Log Factor	The ratio represented by the true distance divided by the log distance. [14]
1235	Lower Limb	See limb. [14]
1236	Mean Draft	See draft. [14]
1237	Mesosphere	The atmospheric layer between the stratosphere and the thermosphere. Located at an average elevation between 50 and 80 km above the earth's surface. [1]
1238	Oceanology	See oceanography. [14]
1239	Open Coast	A coast that is not sheltered from the sea. [14]
1240	Orthodrome	Any line on a chart representing a great circle track between two points. [14]
1241	Orthogonal	(Adj.). At right angles; rectangularly meeting, crossing, or lying at right angles. [14]
1242	Patent Log	See log. [14]
1243	Permafrost	A layer of soil or bedrock at a variable depth beneath the surface of the earth in which the temperature has been below freezing continuously from a few to several thousands of years. Permafrost exists where the summer heating fails to descend to the base of the layer of frozen ground. [14]
1244	Radiosonde	Instrument carried through the atmosphere, equipped with devices permitting one or several meteorological elements (pressure, temperature, humidity, etc.) To be determined, and provided with a radio transmitter for sending this information. [14]
1245	Rafted Ice	Type of pressure ice formed by one floe overriding another. [14]
1246	Rear Light	See light(s): range. [14]
1247	Red Sector	A sector of the circle of visibility of a navigational light in which a red light is exhibited. Such sectors are designated by their limiting bearings, as observed at some point other than the light. Red sectors are often located so that they warn of danger to vessels. [14]
1248	Roof Prism	A type of prism in which the image is reverted by a roof, that is, two surfaces inclined at 90° to each other. [14]
1249	Seismology	The science and study of earthquakes, and their causes and effects and related phenomena. [14]
1250	Settlement	The general lowering in level of a moving vessel, relative to what its level would be were it motionless. Settlement is due to the regional depression of the surface of the water in which the ship moves. It is not an increase in displacement. Settlement is a factor to be reckoned in echo sounding. [14]
1251	Sight Line	See collimation: line of. [14]
1252	Slack Tide	See slack water. [14]
1253	Solar Year	See year: tropical. [14]
1254	Sonic Wave	See wave: sound. [14]
1255	Sound Buoy	See buoy. [14]
1256	Speed Line	A line of position approximately perpendicular to the course. [14]
1257	Stadia Rod	See stadia. [14]
1258	Star Globe	A small globe representing the celestial sphere, on which the apparent positions of the stars are indicated. It is usually provided with graduated arcs and a suitable mount for determining the approximate altitude and azimuth of the stars, to serve as a star finder. Also called celestial globe. [14]
1259	Steel Tape	See tape. [14]
1260	Stereopair	See stereoscopic pair. [14]
1261	Stop Watch	See watch. [14]
1262	Storm Tide	See storm surge. [14]
1263	Storm Wave	See wave. [14]
1264	Sugar Loaf	A descriptive term for a conical hill. [14]
1265	Survey Net	See level net, triangulation net. [14]
1266	Tachymetry	A method of surveying for the rapid determination of distance, direction, and relative elevation of a point with respect to the instrument station by a single observation on a rod or other object at the point. The stadia method of surveying is an example of tachymetry. [14]
1267	Tented Ice	Pressure ice in which two ice floes have been pushed into the air, leaving an air space underneath. [14]
1268	Tidal Rise	See rise of tide. [14]
1269	Variometer	An instrument for comparing magnetic forces, especially of the earth's magnetic field. [14]
1270	Wall Cloud	An area of rotating clouds that extends beneath a supercell thunderstorm and from which a funnel cloud may appear. Also called a collar cloud and pedestal cloud. [1]
1271	Warm Front	Any non-occluded front which moves in such a way that warmer air replaces colder air. [14]
1272	Watch Buoy	See station buoy. [14]
1273	Wave Group	A series of waves in which the wave direction, wavelength, and wave height vary only slightly. [14]
1274	Westerlies	One, lying between the approximate latitudes 35oand 65o in each hemisphere, in which the air motion is mainly from west to east, especially in the high troposphere and low stratosphere. Near the earth's surface, the zone is particularly well marked in the southern hemisphere. [14]
1275	Westerlies	The dominant westerly winds that blow in the middle latitudes on the poleward side of the subtropical high- pressure areas. [1]
1276	X-Parallax	See parallax: absolute stereoscopic. [14]
1277	Age Of Tide	See age of phase inequality. [14]
1278	Aiming Line	See collimation: line of. [14]
1279	Air Density	The ratio of the mass of a substance to the volume occupied by it. Air density is usually expressed as g/cm3 or kg/m3. Also see density. [1]
1280	Air Sextant	See sextant. [14]
1281	Altocumulus	A middle cloud, usually white or gray. Often occurs in layers or patches with wavy, rounded masses or rolls. [1]
1282	Altostratus	A middle cloud composed of gray or bluish sheets or layers of uniform appearance. In the thinner regions, the sun or moon usually appears dimly visible. [1]
1283	Anticyclone	Region of the atmosphere where the pressure is high relative to the surrounding region at the same level. It is represented on a synoptic chart by a system of isobars at a specified level or of contours at a specified pressure which enclose relatively high values of pressure or level. Also called high. [14]
1284	Area Survey	A method of bottom relief survey consisting of surveying overlapping strips which allow soundings to be obtained with a specified accuracy at any position of the area under survey. [14]
1285	Astigmatism	An aberration affecting the sharpness of images for objects off the axis, in which the rays passing through different meridians of the lens come to focus in different planes. [14]
1286	Attenuation	A lessening in amount, particularly the reduction of the amplitude of a wave or the intensity of light or sound with distance from the origin. [14]
1287	Basal Plane	See epipolar plane. [14]
1288	Bifurcation	A division into two branches. [14]
1289	Box Compass	See declinatoire. [14]
1290	Buoy: Sound	A buoy equipped with a characteristic sound signal. Sound buoys may be further classified according to the manner in which the sound is produced, such as bell, gong, horn, trumpet, or whistle buoy. [14]
1291	Buoy: Super	A very large buoy designed to carry a signal light of high luminous intensity at a high elevation. See also large automatic navigation buoy (lanby). [14]
1292	Check Angle	A third angle taken to a fourth point as a check to a three-point fix. [14]
1293	Coast Pilot	(US Terminology). A descriptive book for the use of mariners, containing detailed information of coastal waters, harbor facilities, etc., of an area. Such books are prepared by the national ocean service for waters of the US. And its possessions. See also sailing directions. [14]
1294	Correlation	The removal of discrepancies that may exist among survey data, so that all parts are interrelated without apparent error. [14]
1295	Cross Hairs	See cross wires. [14]
1296	Danger Zone	See danger area. [14]
1297	Datum Point	See reference point. [14]
1298	Delineation	In cartography, the visual selection and distinguishing of map worthy features on various possible source materials by outlining the features on the source material, or on a map manuscript (as when operating a stereoscopic plotting instrument); also a preliminary step in compilation. [14]
1299	Dipsey Lead	See lead: deep sea. [14]
1300	Diurnal Arc	See arc: astronomical. [14]
1301	Drying Reef	A reef or part thereof which dries at low water. [14]
1302	Forel Scale	A colour scale employed as a means of determining the colour of sea water. [14]
1303	Front Light	See light(s): range. [14]
1304	Frost Point	The temperature to which atmospheric moisture must be cooled to reach the point of saturation with respect to ice. [14]
1305	Grid Method	In photogrammetry, a method of plotting detail from oblique photographs by superimposing a perspective of a map grid on a photograph and transferring the detail by eye, that is, by using the corresponding lines of the map grid and its perspective as placement guides. See also grid: per-spective. [14]
1306	Hydrosphere	The waters of the earth's surface collectively. The 'water sphere' in comparison and contrast with lithosphere and atmosphere. [14]
1307	Index Glass	See index mirror. [14]
1308	Isomagnetic	(Adj.). Of or pertaining to lines connecting points of equality in some magnetic element. [14]
1309	Isomagnetic	(n.). See isomagnetic line. [14]
1310	Land Breeze	Wind of coastal regions blowing at night from the land towards a large water surface as a result of nocturnal cooling of the land surface. [14]
1311	Land Survey	See survey: cadastral. [14]
1312	Layer Depth	In oceanography, the thickness of the mixed layer; or the depth to the top of the thermocline. [14]
1313	Marker Buoy	A temporary buoy used in surveying to mark a location of particular interest such as a shoal or reef. See also station buoy. [14]
1314	Occultation	The concealment or extinguishment of the light of an aid to navigation during the dark periods of its cycle. In astronomy, the concealment of a celestial body by another which crosses the line of view. Thus, the moon occults a star when it passes between the observer and the star. [14]
1315	Ocean Water	Water having the physical-chemical characteristics of the open sea, where continental influences are at a minimum. [14]
1316	Planisphere	A map or chart that is the projection of all or part of a sphere on a plane. A representation, on a plane, of the celestial sphere, especially one on a polar projection, with means provided for making certain measurements such as altitude and azimuth. See star finder. [14]
1317	Plumb Point	See nadir: photograph. [14]
1318	Radial Plot	See radial triangulation. [14]
1319	Radio Range	A radio facility the emissions of which are intended to provide a definite course guidance. [14]
1320	Radio Stars	Sources of radio waves existing in the universe. The position of many of the radio stars have been plotted but their signals are generally very weak. [14]
1321	Restitution	The process of determining the true planimetric position of objects whose images appear on photographs. Restitution corrects for distortion resulting from both tilt and relief displacement. [14]
1322	Rip Current	See current. [14]
1323	Safety Zone	The area around an offshore installation within which vessels are prohibited from entering without permission. Special regulations protect installations within a safety zone and vessels of all nationalities are required to respect the zone. [14]
1324	Scale Error	The difference between the principal scale and the particular scale resulting from projection distortion. [14]
1325	Secchi Disc	A white, black, or varicolored disc, 30 centimeters in diameter, used to measure water transparency (clarity). The disc is lowered in the water and the depth (in meters) at which it disappears from sight is averaged with the depth at which it reappears. This average value is used to represent sea water transparency. [14]
1326	Selenotrope	A device used in geodetic surveying for reflecting the moon's rays to a distant point, to aid in long-distance observations. [14]
1327	Slope Angle	The angle between a slope and the horizontal. [14]
1328	Speedometer	An odometer recording the speed of a craft by a process of differentiation. [14]
1329	Spot Height	See spot elevation. [14]
1330	Squaring Up	See squares: method of. [14]
1331	Star Finder	A device to facilitate the identification of stars. Sometimes called a star identifier. See planisphere. [14]
1332	Stereomodel	See stereoscopic image. [14]
1333	Stratopause	Top of the inversion layer in the upper stratosphere, at about 50-55 km. [14]
1334	Summer Time	See time: daylight saving. [14]
1335	Sumner Line	A celestial line of position, particularly one established by the Sumner method. Named after captain Thomas h. Sumner, the discoverer of the line of position by celestial observation. [14]
1336	Sunken Rock	A rock potentially dangerous to surface navigation, the summit of which is below the lower limit of the zone for rock awash. [14]
1337	Tape: Invar	Any survey tape made of invar. [14]
1338	Tape: Steel	Any survey tape made of steel. [14]
1339	Tidal Level	Depth or height contours defined by the rise and fall of the astronomical tide. [13]
1340	Time: Civil	Solar time in a day (civil day) that begins at midnight. [14]
1341	Transceiver	A combination transmitter and receiver in a single housing, with some components being used by both parts. See transponder. [14]
1342	Valley Line	See talweg. [14]
1343	W/T Station	See radio station. [14]
1344	Waning Moon	See phases of the moon. [14]
1345	Wave Trough	See trough. [14]
1346	Wave: Sound	A mechanical disturbance advancing with finite velocity through an elastic medium and consisting of longitudinal displacements of the ultimate particles of the medium, that is, consisting of compressional and rare-factional displacements parallel to the direction of advance of the disturbance; a longitudinal wave. Also called sonic wave, or acoustic wave. [14]
1347	Waxing Moon	See phases of the moon. [14]
1348	Wet Compass	See compass: liquid. [14]
1349	Wind Set-Up	The vertical rise in the still water level on the leeward side of a body of water caused by wind stresses on the surface of the water. The difference in still water levels on the windward and the leeward sides of a body of water caused by wind stresses on the surface of water. Synonymous with wind tide. Wind tide is usually reserved for use on the ocean and large bodies of water. Wind set-up is usually reserved for use on reservoirs and smaller bodies of water. See tide: meteorological. [14]
1350	Wire: Invar	A wire made of invar metal used in measurement of geodetic bases. [14]
1351	Grid: Universal Transverse Mercator (Utm)	A grid system in which a grid network is applied to transverse Mercator projections of zones of the earth's surface extending to 80° n. And s. Latitudes. [14]
1352	d50	One of the sediment characteristic which is in the median grain size. ; The portions of particles with diameters smaller and larger than this value are 50%. Also known as the median diameter. [24]
1353	Gut	A narrow passage such as a strait or inlet. A channel in otherwise less deep water, generally formed by water in motion. [14]
1354	Kay	See cay. [14]
1355	Ohm	The unit of electrical resistance in the si system. [14]
1356	Voe	An inlet, bay, or creek. [14]
1357	Arpa	See automatic radar plotting aid. [14]
1358	Bias	The distortion of a result through negligence of a factor usually introducing a systematic error of unchanging magnitude and sign throughout a given series of observations. [14]
1359	Blip	Indication of a signal on the scope of an electronic instrument, produced by a short sharply-peaked pulse of voltage. [14]
1360	Crag	A steep or precipitous rugged rock. [14]
1361	Dyke	See dike. [14]
1362	Firn	Old snow which has become granular and dense under the action of various processes of melting and refreezing, also including sublimation. [14]
1363	Font	Complete assortment of all the different characters of a particular size and style of type. [14]
1364	Glen	A narrow, secluded valley. [14]
1365	Gyre	A closed circulatory system, but larger than a whirlpool or eddy. [14]
1366	Haze	Suspension in the atmosphere of extremely small, dry particles which are invisible to the naked eye but are numerous enough to give the sky an appearance of opalescence. [14]
1367	Hulk	the hull of a wrecked or condemned ship, from which the fittings and superstructure have usually been removed, which is moored in a permanent position or grounded. [14]
1368	Int1	the compendium of symbols, abbreviations and terms to be used on paper and raster nautical charts, for use principally as a reference by mariners, as derived from the "regulations of the IHO for international (int) charts and chart specifications of the IHO" (IHO s-4). [14]
1369	Lull	A momentary decrease in the speed of the wind. [14]
1370	Ooze	A soft mud or slime. A fine-grained pelagic sediment containing undissolved sand- or silt-sized, calcareous or siliceous skeletal remains of small marine organisms in proportion of 30 percent or more, the remainder being amorphous clay-sized material. [14]
1371	Snag	A tree or branch embedded in a river or lake bottom and not visible on the surface, forming thereby a hazard to boats. [14]
1372	Spit	A small point of land or narrow shoal projecting into a body of water from the shore. [14]
1373	Sway	The side-to-side bodily motion of a ship, independent of rolling, caused by uniform pressure being exerted all along one side of the hull. [14]
1374	Thaw	Melting of snow and/or ice, at the earth's surface, following a temperature rise above 0°c. [14]
1375	Trim	The way in which a ship floats on the water, in relation to her fore-and-aft line, whether on an even keel or down by the bow or by the stern. [14]
1376	Tufa	A chemical sedimentary rock composed of calcium carbonate or silica, precipitated from percolating ground water or from a spring. [14]
1377	Wadi	A watercourse that is permanently dry or dry except for the rainy season. [14]
1378	Wake	The path of disturbed water or air behind a craft in motion. [14]
1379	Watt	The unit of power in the si system. [14]
1380	Apron	1. A gently dipping featureless surface, underlain primarily by sediment, at the base of any steeper slope. 2. The area of wharf or quay for handling cargo. 3. A sloping underwater extension of an iceberg. 4. An outwash plain along the front of a glacier. [14]
1381	Apsis	(pl. Apsides) see line of apsides. [14]
1382	Awips	Acronym for advanced weather interactive processing system. New computerized system that integrates and processes data received at a weather forecasting office from nexrad, asos, and analysis and guidance products prepared by nmc. [1]
1383	Barye	Pressure unit in the cgs system. [14]
1384	Bight	A bend or curve in the coastline, a bend in a river, etc. In ice terminology, an extensive crescent-shaped indentation in the ice edge formed either by wind or current. [14]
1385	Bluff	A cliff or headland with an almost perpendicular face. [14]
1386	Butte	An isolated flat-topped hill, similar to, but smaller than a mesa. [14]
1387	Cairn	A mound of stones, usually conical or pyramidal, raised as a landmark or to designate a point of importance in surveying. [14]
1388	Chaos	The property describing a system that exhibits erratic behavior in that very small changes in the initial state of the system rapidly lead to large and apparently unpredictable changes sometime in the future. [1]
1389	Crack	Any fracture or rift in sea ice not sufficiently wide to be described as a lead. [14]
1390	Creek	A comparatively narrow inlet, of fresh or salt water, which is tidal throughout its whole course. A small tributary. A small, narrow bay which extends farther inland than a cove. [14]
1391	Elbow	A sudden turn in a channel, river, or shoreline. [14]
1392	Farad	The unit of electrical capacitance, in the si system. [14]
1393	Firth	A Scottish word: an arm of the sea; an estuary of a river. [14]
1394	Fjord	See fiord. [14]
1395	Flume	An inclined channel for conveying water from a distance to be utilized for power, transportation, irrigation, etc. [14]
1396	Gamma	Photographic term for negative contrast resulting from development, and not the contrast of the subject itself; a numerical measure of contrast in the development of a negative. A small unit of magnetic field intensity generally used in describing the earth's magnetic field. It is defined as being equal to 10-5 oersted. [14]
1397	Gully	Small valley cut into soft sediments on the continental shelf or continental slope. [14]
1398	Henry	The unit of electrical inductance in the si system. [14]
1399	Knoll	A relatively small isolated elevation of a rounded shape. On the sea floor, an elevation somewhat smaller than a seamount and of rounded profile characteristically isolated or as a cluster. Also called hill. [14]
1400	Lough	Irish equivalent of the Scottish loch. [14]
1401	Lumen	The unit of luminous flux in the si system. [14]
1402	Lurch	A sudden roll to one side. See list. [14]
1403	Moire	Undesirable patterns occurring when reproductions are made from halftone proofs or steel engravings, caused by conflict between the ruling of the halftone screen and the dots or lines of the original; a similar pattern occurring in multicolor halftone reproductions and usually due either to incorrect screen angles or misregister of the colour impressions during printing. [14]
1404	Mouse	In computer systems, a pointing device operated by moving on a flat surface. See also cursor, joy-stick. [14]
1405	Shuga	An accumulation of spongy white ice lumps, a few centimeters across; the lumps are formed from grease ice or slush and sometimes from anchor ice rising to the surface. [14]
1406	Sleet	A type of precipitation consisting of transparent pellets of ice 5 mm or less in diameter. Same as ice pellets. [1]
1407	Slime	Soft, fine, oozy mud or other substance of similar consistency. [14]
1408	Squat	For a ship underway, the change of level of the bow and stern from the still water condition in re-sponse to the elevation and depression of the water level about the hull resulting from the bow and stern wave systems. [14]
1409	Talus	A slope. A sloping mass of detritus lying at the base of a cliff or the like, and consisting of material which has fallen from its face; also the slope or inclination of the surface of such a mass. [14]
1410	Tesla	The unit of magnetic flux density in the si system. [14]
1411	Varve	A sedimentary deposit, bed, or lamination deposited in one season. It is usually distinguished by colour or composition and used as an index to changes in the depositional environment. [14]
1412	Virga	Precipitation that falls from a cloud but evaporates before reaching the ground. (see fall streaks.) [1]
1413	Weber	The unit of magnetic flux in the si system. [14]
1414	Wedge	In optics, a refracting prism of very small deviation such as those used in the eyepiece of some stereoscopes. In meteorology, term synonymous with ridge, though usually applied to a fast-moving ridge between two depressions or troughs. [14]
1415	Billow	A great wave. [14]
1416	Boring	Forcing a vessel under power through ice. [14]
1417	Camber	A small basin, usually with a narrow entrance, situated inside a harbor. [14]
1418	Choppy	(adj). Of the sea, having short, abrupt, breaking waves dashing against each other. [14]
1419	Cobble	A naturally rounded stone larger than a pebble. [14]
1420	Corona	Photometeor formed by one or more sequences (seldom more than three) of coloured rings of relatively small radius, centered on the sun or moon. [14]
1421	Crater	Bowl-shaped cavity, at the summit or on the side of a volcano. [14]
1422	Cupola	A small dome-shaped tower or turret rising from a building. [14]
1423	Cutter	A boat belonging to a warship. [14]
1424	Dries'	see covers and uncovers. [14]
1425	Duplex	A method in which telecommunication between two stations can take place in both directions simultaneously. [14]
1426	Fading	Loss of strength in received signals due to temporary variations in the conditions of propagation. [14]
1427	Fender	A device let down between the side of a ship or a wharf or other ship to protect from chafing when ships are lying alongside or to take the shock of a bump when going alongside. [14]
1428	Haboob	A dust or sandstorm that forms as cold downdrafts from a thunderstorm turbulently lift dust and sand into the air. [1]
1429	Homing	Navigation toward a point by maintaining constant some navigational coordinate(s), usually bearing. The procedure of using the direction-finding equipment of one radio station with the emission of another radio station, where at least one of the stations is mobile, and whereby the mobile station proceeds continuously towards the other station. [14]
1430	Klaxon	A small power fog signal sometimes operated by hand. [14]
1431	League	A varying measure of distance, usually about three miles. [14]
1432	Leeway	The leeward motion of a vessel due to wind. It may be expressed as distance, speed, or angular difference between course steered and course through the water. Drift angle. Also called drift. [14]
1433	Lipper	Slight ruffling or roughness on a water surface. Light spray from small waves. Also called leaper. [14]
1434	Marina	A harbor facility for small boats, yachts, etc., where supplies, repairs, and various services are available. [14]
1435	Massif	A large mountain-mass; the central mass of a mountain; a compact and more or less independent portion of a range. [14]
1436	Newton	The unit of force in the si system. [14]
1437	Nipped	(Adj. And adv.). Said of a ship which is beset when ice forcibly presses against it. See beset, icebound. [14]
1438	Offing	That part of the visible sea a considerable distance from the shore, or that part just beyond the limits of the area in which a pilot is needed. [14]
1439	Photic	(Adj.). Of sea water, that is penetrated or influenced by sunlight. [14]
1440	Photon	A discrete quantity of energy that can be thought of as a packet of electromagnetic radiation traveling at the speed of light. [1]
1441	Polder	Land reclaimed from the sea or other body of water by the construction of an embankment to restrain the water. See dike. [14]
1442	Puddle	An accumulation on the ice of melt water, mainly due to melting snow, but in the more advanced stages also to the melting of ice. Initial stage consists of patches of melted snow. [14]
1443	Pulsar	A rotating neutron star emitting electromagnetic radiation in regular pulses related to its rotational period. [14]
1444	Pumice	An excessively cellular, glassy lava. It is very light and can float on water until it becomes waterlogged and sinks. [14]
1445	Q-Wave	See wave: love. [14]
1446	Radome	A dome, usually of glass reinforced plastic, housing a radar aerial. These domes are often prominent. The term is also used for domes or pods housing similar equipment in ships or on aircraft. [14]
1447	Ravine	In general, any steep-sided valley. [14]
1448	Refuge	A place of safety for a vessel in danger. [14]
1449	Reseau	A network. In photography, a glass plate on which is etched a network of fine lines. Sometimes used as a focal-plane plate to provide a means of calibrating film distortion. [14]
1450	Rodman	A person using a surveying rod. [14]
1451	Rotors	Turbulent eddies that form downwind of a mountain chain, creating hazardous flying conditions. [1]
1452	Rubble	Fragments of hard sea ice, roughly spherical and up to 1,5 meters (5 feet) in diameter, resulting from the disintegration of larger ice formations. When afloat, commonly called brash ice. Loose angular rock fragment. [14]
1453	Runnel	The smallest of natural streams; a brook or run. A trough or corrugation formed in the foreshore or in the bottom, immediately offshore, formed by waves or tidal currents. [14]
1454	Salina	A salt marsh or salt pond separated from the sea but flooded by high tides. [14]
1455	School	See shoal. [14]
1456	Slough	A minor marshland or tidal waterway which usually connects other tidal areas; often more or less equivalent to a bayou. Quagmire, swamp, miry place. [14]
1457	Sluice	Sliding gate or other contrivance for changing the level of a body of water by controlling flow into or out of it. [14]
1458	Steppe	An area of grass-covered, treeless plains that has a semiarid climate. [1]
1459	Strath	A broad elongated depression with relatively steep walls located on a continental shelf. The longi-tudinal profile of the floor is gently undulating with greatest depths often found in the inshore portion. [14]
1460	Stylus	A pointer that is operated by placing it in a display space or a tablet. [14]
1461	Sundog	A colored luminous spot produced by refraction of light through ice crystals that appears on either side of the sun. Also called parhelia. [1]
1462	Tie In	(v.i.). See tie. [14]
1463	Tongue	A projection of the ice edge up to several kilometers in length, caused by wind and current. A relatively narrow strip of land. An inlet. A narrow, rapid current. A protrusion of water into a region of different temperature. [14]
1464	Trivet	A low support for a surveying instrument which is used where a tripod cannot be used. [14]
1465	Typhon	A diaphragm horn which operates under the influence of compressed air or steam. Called siren in Canadian terminology. Also called Tyfon. [14]
1466	Varsol	An oil used as the liquid in some modern magnetic compasses. [14]
1467	Veneer	A thin layer of sediment covering a rocky surface. [14]
1468	Vertex	(pl. Vertices). The highest point; the vertices of a great circle are the points nearest the pole. See apex. [14]
1469	Aphotic	(Adj.). Without light. [14]
1470	Blow Up	Enlarge photographically. [14]
1471	Boulder	A rounded rock with a diameter of 256 millimeters (about 10 inches) or larger. [14]
1472	Calving	The breaking away of a mass of ice from a glacier, ice front, or iceberg. [14]
1473	Clutter	Confused unwanted echoes on a radar display. [14]
1474	Console	The housing of the main operating unit of electronic equipment, in which indicators and general controls are located. A portion of a computer used to control the machine manually. [14]
1475	Coulomb	The unit of electric charge in the si system. [14]
1476	Damping	The dissipation of energy with time or distance. The progressive reduction of amplitude of oscillations, waves, etc. [14]
1477	Decibar	One-tenth of a bar. [14]
1478	Decibel	See bel. [14]
1479	Derecho	Strong, damaging, straight-line winds associated with a cluster of severe thunderstorms that most often form in the evening or at night. [1]
1480	Derrick	A tall pyramid of latticed steel mounted over a borehole. [14]
1481	Diopter	A unit of refractive power of an optical system in the si system. [14]
1482	Dog Leg	A leg which does not lead directly to the destination or way point. [14]
1483	Dredger	A vessel or floating structure equipped with machinery for excavating ditches or canals, deepening channels and harbors, and removing solid matter from the bottom of a water area. Also called a dredge. [14]
1484	End Lap	See overlap. [14]
1485	Fog Gun	A gun used as a fog signal. [14]
1486	Freshet	An area of comparatively fresh water at or near the mouth of a stream flowing into the sea. A flood or overflowing of a river caused by heavy rains or melted snow. [14]
1487	Glitter	The spots of light reflected from a point source by the surface of the sea. [14]
1488	Granite	Light-coloured, acidic igneous rock mineralogically composed primarily of quartz and potassium-sodium rich feldspars in which the mineral grains are visible to the naked eye (phaneritic texture). [14]
1489	Growler	A piece of ice almost awash, smaller than a bergy bit. [14]
1490	Holiday	An unintentional unsurveyed area within a given hydrographic survey where the spacing between sounding lines or surveys exceeds the maximum allowable limits. [14]
1491	Hunting	Fluctuation about a midpoint due to instability, as oscillations of the needle of an instrument about the zero point, or alternate lead and lag of a synchronous motor with respect to the alternating current. [14]
1492	Indelta	Inland area where a river subdivides (now in common use, especially in Australia). [14]
1493	Isogriv	A line connecting points of equal grid variation. [14]
1494	Isotope	Two or more nuclides having the same atomic number, hence constituting the same element, but differing in mass number. [14]
1495	Isthmus	A narrow strip of land connecting two larger bodies of land. [14]
1496	Kedging	Moving a vessel by laying out an anchor and then hauling the vessel up to the anchor. [14]
1497	La Niña	A condition where the central and eastern tropical pacific ocean turns cooler than normal. [1]
1498	Locking	In electronic navigation, a term describing the condition of two transmitters when their signals maintain a stable phase relationship. One station is then said to be locked to the other. [14]
1499	Logging	1. Gauging ship's speed with a log. 2. Record events. [14]
1500	Lowland	Low and relatively level land at a lower elevation than adjoining districts. [14]
1501	Magenta	Adj.). A mixture of red and blue in equal parts. [14]
1502	Meander	(often in plural). A winding, convolution or winding course, as of a stream. A deviation of the flow pattern of a current. [14]
1503	Mock-Up	A model of something to be used for testing or study. [14]
1504	Monsoon	Wind of the general circulation of the atmosphere, typified by the seasonal persistence of a given wind direction and by a pronounced change in this direction from one season to another. The term is generally confined to those cases in which the primary cause is the differential heating (changing in nature from summer to winter) of a continent relative to a neighbouring ocean. [14]
1505	Montage	A series of related pieces of copy appearing as one to tell a complete story. [14]
1506	Narrows	A navigable narrow part of a bay, strait, river, etc. [14]
1507	Nipping	The closing of ice around a ship so that the ship is beset and subjected to pressure from the ice. [14]
1508	Nodules	In oceanography, concretionary lumps of manganese, cobalt, iron, and nickel found widely scattered on the ocean floor. Rocks of various sizes and shapes often are encrusted with these metals. [14]
1509	Nowcast	Short-term weather forecasts varying from minutes up to a few hours. [1]
1510	Nunatak	An isolated hill or mountain peak of rock projecting above an inland ice sheet. [14]
1511	Oersted	The cgs unit of magnetic field intensity in the si system. [14]
1512	Old Ice	Any sea ice more than 1 year old. [14]
1513	Outcrop	Naturally protruding, or erosional exposed or uncovered part of a rock, most of which is covered by overlying material. [14]
1514	Pontoon	Floating structure, usually rectangular in shape which serves as landing, pierhead or bridge support. [14]
1515	Pricker	A pointed tool used instead of a pencil for laying off finer and more accurate lines on a plotting sheet. [14]
1516	Quayage	A comprehensive term embracing all the structures in a port alongside which vessels can lie. [14]
1517	Rainbow	Groups of concentric arcs with colors ranging from violet to red, produced on a "screen" of water drops (raindrops, droplets of drizzle or fog) in the atmosphere by light from the sun or moon. [14]
1518	Red Mud	See mud. [14]
1519	Rivulet	A small river. [14]
1520	Road(S)	See roadstead. [14]
1521	Sanding	An irregular dot pattern used on some of the early hydrographic surveys to accentuate the area between the high- and low-water lines. [14]
1522	Savanna	A tropical or subtropical region of grassland and drought-resistant vegetation. Typically found in tropical wet- and-dry climates. [1]
1523	Sea Fog	See fog. [14]
1524	Seamark	An aid to navigation located with the express purpose of being visible from a distance to seaward. Often erected in shoal water rather than on land. [14]
1525	Seaport	A port on or near the sea and readily accessible to seagoing vessels. [14]
1526	Shimmer	Apparent fluttering of objects at the earth's surface, when they are viewed in an almost horizontal direction above strongly heated surfaces. [14]
1527	Shingle	Rounded, often flat waterworn rock fragments larger than approximately 16 millimeters. [14]
1528	Siemens	The unit of conductance in the si system. [14]
1529	Sigma-T	Symbol ïƒ t). A conveniently abbreviated value of the density of a sea water sample of temperature t and salinity s: ïƒt = (rho(s,t)-1) * 1000 , where rho(s,t) is the value of the sea water density in cgs units at standard atmospheric pressure. If, for example, rho(s,t) = 1.02648, then ïƒt = 26.48. [14]
1530	Simplex	A method in which telecommunication between two stations takes place in one direction at a time. [14]
1531	Sparker	An echo sounder which uses an electrical spark discharge as the sound source. A recorder produces a chart which represents a vertical cross section of the geological structure beneath the water bottom. [14]
1532	Spindle	A spar serving as a beacon. A slender pin or rod, as one constituting part of a machine. [14]
1533	Splines	Flexible rulers or interpolation algorithm used to draw smooth curves between points when constructing e.g. Hyperbolic lattices. [14]
1534	Stratum	(pl. Strata). A single sedimentary bed or layer of generally homogenous rock, independent of thickness. [14]
1535	Subplan	An inset on a survey sheet used to extend the survey coverage shown on the sheet, or to show small congested areas at enlarged scales. [14]
1536	Sundial	An instrument that indicates time by the position of the shadow of a pointer or gnomon cast by the sun on the face of a dial marked in hours. [14]
1537	Syntony	The situation of two or more oscillating circuits having the same resonant frequency. [14]
1538	Thalweg	See talweg. [14]
1539	Tideway	A channel through which a tidal current runs. [14]
1540	Tillite	Rock formed of consolidated or lithified till and generally a record of a glacial epoch, older than that of the quaternary. [14]
1541	Tonnage	The carrying capacity of ships. [14]
1542	Tripton	Collectively, all of the dead suspended particulate matter in aquatic habitats. [14]
1543	Viaduct	A structure consisting of a series of arches or towers supporting a roadway, waterway, etc., across a depression, etc. [14]
1544	Westing	The distance a craft makes good to the west. The opposite is easting. [14]
1545	Wet Fog	See fog. [14]
1546	Y-Level	See levelling instrument: y level. [14]
1547	Aerology	Study of the free atmosphere. [14]
1548	Aerovane	A wind instrument that indicates or records both wind speed and wind direction. Also called a skyvane. [1]
1549	Affluent	A stream flowing into a larger stream or lake; a tributary. [14]
1550	Analemma	A scale of the sun's daily declination drawn from tropic of cancer to tropic of Capricorn on terrestrial globes. An orthographical projection of the sphere made on the plane of the meridian, the eye being supposed to be an infinite distance and in the east or west point of the horizon. [14]
1551	Array(S)	The order in which equipment (antenna, oceanographic equipment) or mathematical quantities are ordered. [14]
1552	Avulsion	Rapid erosion of shoreland by waves during a storm. [14]
1553	Backwash	Water or waves thrown back by an obstruction such as a ship, breakwater, cliff, etc. [14]
1554	Bar Buoy	A buoy marking the location of a bar. [14]
1555	Barogram	Record made by a barograph. [14]
1556	Base Map	See map. [14]
1557	Beam Sea	Waves moving in a direction approximately 90° from the heading. [14]
1558	Blizzard	Violent and very cold wind which is laden with snow, some part, at least, of which has been raised from snow-covered ground. This term originated in north America but has been extended to include similar winds in other countries. [14]
1559	C/A Code	The standard (coarse/acquisition, or clear/access) gps code; a sequence of 1023 pseudo-random binary biphase modulations on the gps carrier at a chip rate of 1.023 MHz, thus having a code repetition period of one millisecond. See also p-code. [14]
1560	Cadastre	A public record of the extent, value, and ownership of land for purposes of taxation. [14]
1561	Causeway	A raised way across low or wet ground or water. [14]
1562	Chaining	See taping. [14]
1563	Clapotis	The french equivalent for a type of standing wave. [14]
1564	Co-Phase	see. CO-TIDAL [14]
1565	Co-Range	Lines on a cotidal chart joining places which have the same tidal range or amplitude. Usually drawn for a particular constituent or tidal condition (e.g. spring tides). [16]
1566	Co-Tidal	Lines on a cotidal chart joining places where tide has the same phase, for example where high water occurs at the same time. Usually drawn for a particular constituent or tidal condition. [16]
1567	Data Set	A logical entity of data consisting of several elements (fields) grouped under one criterion. [14]
1568	Deadbeat	(Adj.). Aperiodic, or without a period. [14]
1569	Deadhead	(1) a block of wood used as anchor buoy. (2) a bollard. [14]
1570	Diaphone	A device operated by compressed air for producing a distinctive fog signal. [14]
1571	Doldrums	The region near the equator that is characterized by low pressure and light, shifting winds. [1]
1572	Doldrums	Zone of calm or light variable winds, in the lower atmospheric layers, situated near the thermal equator; the zone follows, with slight time lag, the annual meridional fluctuation of the thermal equator. [14]
1573	Duplexer	A switching device used to connect a transmitter and a receiver to the same antenna. [14]
1574	Fog Bank	Fog, generally caused by local conditions, which extends over a small area some hundreds of meters wide. [14]
1575	Fog Bell	A bell used as a fog signal. [14]
1576	Fog Gong	A gong used as a fog signal. [14]
1577	Fog Horn	A horn used as a fog signal. [14]
1578	Fog: Ice	Suspension of numerous minute ice crystals in the air, reducing the visibility at the earth's surface. [14]
1579	Fog: Sea	Advection fog which forms over the sea. [14]
1580	Fog: Wet	Fog formed of droplets sufficiently large to deposit water on objects. [14]
1581	Foreland	A cape or promontory. [14]
1582	Gram(Me)	A cgs unit of mass equal to one one-thousandth of a kilogram. [14]
1583	Halation	In photography, a spreading of a photographic image beyond its proper boundaries, due especially to reflection from the side of the film or plate support opposite to that on which the emulsion is coated. Particularly noticeable in photographs of bright objects against a darker background. [14]
1584	Halftone	In photography or printing, a technique in which the solid image is broken up by the use of a screen into evenly spaced dots of equal density but of varying size. This gives an illusion of continuous tone. [14]
1585	Hatching	The drawing or engraving of fine, parallel or crossed lines to show shading. [14]
1586	Head Sea	A sea in which the waves move in a direction approximately opposite to the heading. [14]
1587	Heli Pad	A site on which helicopters may land and take off. [14]
1588	Ice Free	Water surface completely free of ice. [14]
1589	Isobront	Line joining, on a chart, places on the earth's surface where, on a given day, the first clap of thunder has been heard simultaneously. In climatology, line drawn on a chart through places which have the same average number of days on which thunder is heard in a given period. [14]
1590	Isostasy	A condition of approximate equilibrium in the outer part of the earth, such that the gravitational effect of masses extending above the surface of the geoid in continental areas is approximately counterbalanced by a deficiency of density in the material beneath those masses while the effect of deficiency of density in the ocean waters is counterbalanced by an excess of density in the material under the oceans. [14]
1591	Joystick	In computer systems, a pointing device operated by pressing a stick in a desired direction. [14]
1592	Keg Buoy	A buoy consisting of a keg to which is attached a small pole with a flag, used by fishermen to mark the position of a trawl line. See dan buoy. [14]
1593	Lake Ice	Ice formed in lakes. [14]
1594	Laterite	A soil formed under tropical conditions where heavy rainfall leaches soluble minerals from the soil. This leaching leaves the soil hard and poor for growing crops. [1]
1595	Lee Tide	See tide: leeward. [14]
1596	Level: Y	See levelling instrument: y level. [14]
1597	Littoral	(Adj.). Of or pertaining to a shore, especially of the sea. [14]
1598	Littoral	(n.). A coastal region. Intertidal zone. [14]
1599	Log Book	Book in which events connected with the ship are entered. Also written as one word. [14]
1600	Log Boom	Heavy logs chained or lashed together and moored or anchored so as to enclose and contain rafted logs. See also boom. [14]
1601	Log Ship	See log chip. Also written as one word. [14]
1602	Make Way	To progress through the water. [14]
1603	Milligal	A unit of acceleration equal to 1/1,000 of a gal, or 1/1,000 centimeter per second, per second. This unit is used in gravity measurement, being approximately one-millionth of the average gravity at the earth's surface. [14]
1604	Mud: Red	A reddish-brown terrigenous deep-sea mud which accumulates on the sea floor in the neighbour-hood of deserts and off the mouths of great rivers; contains calcium carbonate up to 25 per cent. [14]
1605	Nun Buoy	A buoy the above water part of which is in the shape of a cone or a truncated cone. [14]
1606	Parabola	An open curve all points of which are equidistant from a fixed point, called the focus, and a straight line. [14]
1607	Pictomap	A map supplement on which the photographic imagery of a standard photomosaic has been con-verted into interpretable colors and symbols by means of tonal masking techniques. [14]
1608	Pierhead	The outer end of a pier. Also called wharfhead. [14]
1609	Pinpoint	(v.t. And i.). To establish (position) with great accuracy. [14]
1610	Pitching	See pitch. [14]
1611	Planform	The outline or shape of a body of water as determined by the still water level. [14]
1612	Porosity	The ratio of the aggregate volume of pore space in a rock or sediment to its total volume, usually expressed as a percentage. [14]
1613	Psephyte	A coarse fragmental rock (conglomerate) or deposit composed of rounded pebbles. [14]
1614	Q-Factor	The pressure coefficient of the unprotected thermometer expressed in °c. [14]
1615	Quintant	A double-reflecting instrument for measuring angles. It is similar to a sextant, but has an arc of 72°. [14]
1616	Rapid(S)	Portions of a stream with accelerated current where it descends rapidly but without a break in the slope of the bed sufficient to form a waterfall. Usually used in the plural. [14]
1617	Repromat	Reproduction material, generally in the form of positive or negative copies on film or glass for each colour plate, from which a map or chart may be reproduced without redrafting. [14]
1618	Rockweed	One of a group of marine plants, principally of an order (fucales) of the brown algae, mostly multi-branched and leathery, which grow attached to rocks in the intertidal zone by means of an organ called a holdfast. Also called wrack or fucus. [14]
1619	Sandwave	a large wavelike sediment feature in very shallow water and composed of sand. The wavelength may reach 100 meters; the amplitude may be up to 20 meters. Also sand-wave or sand wave. Sometimes called a mega-ripple. [14]
1620	Sea Moat	See moat. [14]
1621	Seashore	The shore of a sea or ocean. [14]
1622	Shelving	A gently sloping area. [14]
1623	Shipyard	A place where ships are built or repaired. [14]
1624	Side Lap	See overlap. [14]
1625	Solenoid	A coil of wire, often helical in form, which becomes an electromagnet when an electric current is passed through it. [14]
1626	Southing	The distance a craft makes good to the south. The opposite is northing. [14]
1627	Steep-To	(Adj.). Precipitous. The term is applied particularly to a shore, bank or shoal that descends steeply to a lower level. [14]
1628	Sternway	Making way through the water in a direction opposite to the heading. [14]
1629	Stooping	Apparent decrease in the vertical dimension of an object near the horizon, due to large inequality of atmospheric refraction in the line of sight to the top and bottom of the object. The opposite is towe-ring. [14]
1630	Subsonic	(Adj.). Designating or of speeds that are less than that of sound. [14]
1631	Swashway	See swash. [14]
1632	Tidemark	A high water mark left by tidal water. The highest point reached by a high tide. A mark placed to indicate the highest point reached by a high tide, or, occasionally, any specified state of tide. [14]
1633	Toponymy	The place names or the study of place names of a country or district. [14]
1634	Towering	Apparent increase in the vertical dimension of an object near the horizon, due to large inequality of atmospheric refraction in the line of sight to the top and bottom of the object. The opposite is stoo-ping. [14]
1635	Undertow	A seaward flow near the bottom of a sloping beach. The subsurface return by gravity flow of the water carried up on shore by waves or breakers. See also backrush. [14]
1636	Wave Age	The state of development of a wind-generated sea surface wave, conveniently expressed by the ratio of wave speed to wind speed. Wind speed is usually measured at about 8 meters above still water level. [14]
1637	Wet Dock	See dock. [14]
1638	Whitecap	A crest of a wave which becomes unstable in deep water, toppling over or breaking. See breaking of waves. [14]
1639	Wireless	See radio. [14]
1640	Advection	The horizontal transfer of any atmospheric property by the wind. [1]
1641	Altimetry	The process of determining the difference of elevation by the use of altimeters. [14]
1642	Ambiguity	Uncertainty of value or meaning because of the possibility of two or more interpretations. The condition when navigational coordinates define more than one position, direction, line of position, or surface of position. [14]
1643	Amidships	At, near, or toward the middle of a ship. [14]
1644	Anemogram	Record of the anemograph. [14]
1645	Angstroem	A unit of length, used especially in expressing the length of light waves, equal to one ten-thousandth of a micron or one hundred-millionth of a centimeter (1 x 10-8 cm). [14]
1646	Anticline	An arch of stratified rock in which the layers bend downward in opposite directions from the crest. [14]
1647	Backshore	That part of a beach which is usually dry, being reached only by the highest tides. Also called back beach. See also foreshore. [14]
1648	Backwater	Water turned back by an obstruction, opposing current, etc. Water held back from the main flow. [14]
1649	Bandwidth	The number of units (hertz, kilohertz, etc.) Of frequency required for transmission. [14]
1650	Bar Check	An on-site calibration method for echo sounders. [14]
1651	Barograph	Recording barometer. [14]
1652	Barotropy	The condition and type of motion in which pressure is constant on surfaces of constant density, e.g. Surface tides. [14]
1653	Base Tilt	See tilt. [14]
1654	Beaconage	A system of beacons. See buoyage. [14]
1655	Beam Wind	Wind blowing in a direction approximately 90° from the heading. [14]
1656	Bell Buoy	See buoy: sound. [14]
1657	Bergy Bit	A massive piece of sea ice or disrupted hummocked ice; also medium-sized piece of floating glacier ice. Generally less than 5 m above sea level, and not more than about 10 m across. [14]
1658	Berm Line	In cartography, the outer edge of vegetation shown as shoreline on charts in marsh or mangrove areas. [14]
1659	Biosphere	Spherical terrestrial layer comprising the lower part of the atmosphere, the seas and the upper layers of the soil within which living organisms can exist naturally. [14]
1660	Black Ice	A thin sheet of ice that appears relatively dark and may form as supercooled droplets, drizzle, or light rain come in contact with a road surface that is below freezing. Also, thin dark-appearing ice that forms on freshwater or saltwater ponds, or lakes. [1]
1661	Boat Grid	See careening grid or gridiron. [14]
1662	Boat Slip	A slipway designed specifically for boats. [14]
1663	Brash Ice	Accumulation of floating ice made up of small fragments not more than 2 meters across; the wreckage of other forms of ice. [14]
1664	Cartogram	A map showing geographical statistics by means of lines, dots, shaded areas, etc. [14]
1665	Cartouche	A panel on a map, often with decoration, enclosing the title or other legends, the scale, etc. [14]
1666	Cold Wave	Marked cooling of the air, or the invasion of very cold air, over a large area. [14]
1667	Collimate	(v.t.). In physics and astronomy, to render parallel to a certain line or direction; to render parallel, as rays of light; to adjust the line of sight of an optical instrument so that it is in the proper position relative to the other parts of the instruments. In photogrammetry, to adjust the fiducial marks of a camera so that they define the principal point. [14]
1668	Condenser	In optics, a lens or lens system designed to concentrate the illumination from a light source on a limited area. In electricity, a device for receiving and storing an electric charge. Also called a capacitor. [14]
1669	Cross Sea	A series of waves or swell crossing another wave system at an angle. [14]
1670	Ctd Probe	Instrument for measuring electrical conductivity, temperature and depth of the sea water. See probe. [14]
1671	Deflector	An instrument for measuring the directive force acting on a magnetic compass on different headings, for use in compass adjustment. [14]
1672	Depressor	A device to maintain a towfish at a given depth. [14]
1673	Detail(S)	In cartography, the items or particulars of information (shown on a map by lines, symbols, and lettering) which, when considered as a whole, furnish the comprehensive representation of the physical and cultural features of the earth's surface. [14]
1674	Dew-Point	The temperature to which air must be cooled at constant pressure and constant water vapor content to reach saturation. [14]
1675	Digitizer	A computer aided device equipped with a digitizing table and a cursor for digitally capturing graphical data (pictures, charts), usually based on vector-techniques (as opposed to a scanner). The digitizing table consists of a gridded electrical network under the table's surface which allows an automatic computation of the planar x/y coordinates of a cursor's position. Lines are sequentially scanned by moving the cursor along the position and identifying the appropriate symbol on a menu. [14]
1676	Dock Sill	The foundation at the bottom of the entrance to a dry dock or lock against which the caisson or gates close. The depth of water controlling the use of the dock or lock is measured from the sill to the surface. [14]
1677	Dock: Wet	A dock in which water can be maintained at any level by closing a gate when the water is at the desired level. [14]
1678	Dry Proof	An impression of a chart pulled from the engraved plate onto a dry sheet of paper. This impression is fainter than a damp-pulled copy and unsuitable for ordinary use but is free from distortion. [14]
1679	Duststorm	Ensemble of particles of dust or sand energetically lifted to great heights by a strong and turbulent wind. Also called sandstorm. Also written as two words. [14]
1680	Dynameter	An instrument for measuring the magnifying power of a telescope. [14]
1681	Edge Wave	See wave. [14]
1682	Embayment	An indentation in a shoreline forming an open bay. [14]
1683	Extrusion	In cartography, the extension of detail outside the neat line. [14]
1684	Filtering	The process of selecting specific data from a specific source in accordance with certain rules, formulae, or algorithms. [14]
1685	Fish Lead	See lead. [14]
1686	Fish Weir	See fish trap. [14]
1687	Float-Off	(British terminology). The paper of a field board when detached from the board on completion of the work for which the field board was prepared. [14]
1688	Foam Line	The front of a wave as it advances shoreward, after it has broken. [14]
1689	Fog Siren	A siren used as a fog signal. [14]
1690	Foul Area	An area of numerous uncharted dangers to navigation. The area charted serves as a warning to the mariner that all dangers are not charted individually and that navigation through the area may be hazardous. The term "foul" should not be applied to a soft continuum with indefinite boundaries such as mud or sand; to areas congested with marine vegetation such as kelp or grass in water; or to materials not likely to cause damage to a vessel. [14]
1691	Free Port	A port where certain import and export duties are waived (unless goods pass into the country) to facilitate re-shipment to other countries. [14]
1692	Frostbite	The partial freezing of exposed parts of the body, causing injury to the skin and sometimes to deeper tissues. [1]
1693	Gamma Ray	See x-rays. [14]
1694	Gelbstoff	Yellowish organic material suspended in sea water which causes greenish colour of the sea water in coastal areas; usually transported into the sea by rivers. [14]
1695	Geomatics	The science and technology of spatial information management, including the acquisition, storage, analysis and processing, display and dissemination of geo-referenced information. [14]
1696	Geosphere	The solid and liquid portions of the earth; the lithosphere plus the hydrosphere. [14]
1697	Gong Buoy	See buoy: sound. [14]
1698	Half Byte	4 bits of a 8 bit byte; usually used to encode the figures 0....9. [14]
1699	Halocline	A vertical gradient of salinity (which is usually positive) in some layer of the body of water, which is appreciably greater than the gradients above and below it. [14]
1700	Head Wind	Wind which blows in a direction opposite to that in which an object is moving, with respect to the earth's surface. [14]
1701	Heat Wave	Marked warming of the air, or the invasion of very warm air, over a large area. [14]
1702	Hodometer	See odometer. [14]
1703	Hook Echo	The shape of a hook on a doppler radar screen that indicates the possible presence of a tornado. [1]
1704	Horn Buoy	See buoy: sound. [14]
1705	Ice Blink	A typical whitish glare on low clouds above an accumulation of distant ice. It is especially glowing when observed on the horizon. [14]
1706	Ice Field	Area of pack ice consisting of any size floes, which is greater than 10 km across. [14]
1707	Ice Limit	The average position of the ice edge in any given month or period based on observations over a number of years. [14]
1708	Ice Storm	Intense formation of ice on objects by the freezing, on impact, of drops of rain or drizzle. [14]
1709	Impedance	The total opposition offered to an alternating current. It may consist of any combination of resistance, inductive reactance, or capacitive reactance. [14]
1710	Index Bar	See index arm. [14]
1711	Index Map	See map. [14]
1712	Ironbound	(Adj.). Said of a rugged, rocky coast which affords no anchorage. [14]
1713	Isoradial	A radial from the isocenter. [14]
1714	Leap Year	See year: civil. [14]
1715	Left Bank	Of a river, the bank of the left-hand side as one proceeds downstream. [14]
1716	Life Buoy	See buoy. [14]
1717	Lithology	The scientific study of rocks. Literally, the science of stones. [14]
1718	Localizer	A radio facility which provides signals for lateral guidance of aircraft with respect to a runway center line. [14]
1719	Log: Chip	A log consisting essentially of a weighted wooden quadrant attached to a bridle in such a manner that it will float in a vertical position, and a log line, speed being measured by casting the quadrant overboard and counting the knots in the line paid out in unit time. [14]
1720	L-Z Graph	A graph used to determine 'in situ' depths of oceanographic observations by the wire depths minus thermometric depth method. [14]
1721	Madrepore	A branching or stag-horn coral, also any perforated stone coral. [14]
1722	Magnetron	An electron tube for converting direct-current energy into radio-frequency energy by means of a magnetic field. [14]
1723	Manoeuvre	Planned and controlled movement of a vehicle. [14]
1724	Manometer	An instrument for measuring pressure of gases and vapors. [14]
1725	Map Nadir	See nadir. [14]
1726	Map Scale	See scale. [14]
1727	Map: Base	A map showing certain fundamental information, used as a base upon which additional data of specialized nature are compiled. Also, a map containing all the information from which maps showing specialized information can be prepared; a source map. [14]
1728	Marigraph	A recording tide gauge. [14]
1729	Mark Boat	A temporary sounding mark consisting of a whaler moored head and stern, with a signal on board. [14]
1730	Mean Noon	See noon. [14]
1731	Megacycle	One million cycles; one thousand kilocycles. The term is often used incorrectly as the equivalent of one million cycles per second. [14]
1732	Mesoscale	The scale of meteorological phenomena that range in size from a few km to about 100 km. It includes local winds, thunderstorms, and tornadoes. [1]
1733	Meteogram	A chart that shows how one or more weather variables has changed at a station over a given period of time or how the variables are likely to change with time. [1]
1734	Meteorite	A meteor that reaches the surface of the earth as a solid particle. [14]
1735	Metrology	The science of weights and measures. [14]
1736	Mock Suns	Name often given to parhelia, paranthelia and anthelia when they are particularly bright. [14]
1737	Multiplex	In photogrammetry, an instrument for making a topographic map from aerial photographs. A three-dimensional optical model of the terrain to be mapped is produced, in miniature, by direct optical projection from a pair of overlapping photographs. This instrument uses the anaglyph principle. [14]
1738	New Chart	See chart. [14]
1739	Open Port	A port which is not icebound during winter. [14]
1740	Open Wave	The stage of development of a wave cyclone (midlatitude cyclonic storm) where a cold front and a warm front exist, but no occluded front. The center of lowest pressure in the wave is located at the junction of the two fronts. [1]
1741	Orography	The branch of physical geography which deals with the formation and features of mountains; the description of mountains. [14]
1742	Overfalls	Short, breaking waves occurring when a strong current passes over a shoal or other submarine obstruction or meets a contrary current or wind. See rips. [14]
1743	Overprint	In cartography, an additional plate, generally in a distinctive colour, printed down on a map or chart which is already complete in itself. Overprints may be used to reproduce specialized information (e.g., to add aeronautical information to a topographic map) or to incorporate revision data without the amendment of existing plates. [14]
1744	Pie Graph	Circular symbol divided into sectors to indicate proportions of a total value. [14]
1745	Plumb Bob	A conical device, usually of brass and suspended by a cord, by means of which a point can be projec-ted vertically into space over relative short distances. Also referred to as plummet. [14]
1746	Quadripod	A four-legged stand for triangulation, signals, etc. [14]
1747	Quenching	The great reduction in underwater sound transmission or reception resulting from absorption and scattering of sound energy by air bubbles entrapped around the sonar dome. See attenuation. [14]
1748	Quicksand	A loose mixture of sand and water that yields to the pressure of heavy objects. Such objects are difficult to extract once they begin sinking. [14]
1749	Reed Horn	A horn that produces sound by means of a steel reed vibrated by air under pressure. [14]
1750	Rill Mark	A small groove, furrow or channel made in mud or sand on a beach by tiny streams following an outflowing tide. [14]
1751	Safetynet	The international service for the broadcast and automatic reception of maritime safety information via the inmarsat egc system in waters where an international navtex service is not provided. [14]
1752	Salt Pans	Shallow pools of brackish water used for the natural evaporation of sea water to obtain salt. [14]
1753	Sand Dune	A ridge of sand piled up by the action of wind on sea coasts or in deserts. [14]
1754	Sea Scarp	See escarpment. [14]
1755	Semaphore	Any apparatus for signaling. [14]
1756	Shoreface	The narrow zone seaward from the low tide shoreline, permanently covered by water, over which the beach sands and gravels actively oscillate with changing wave conditions. [14]
1757	Siltation	The deposition or accumulation of silt that is suspended in a body of water. [14]
1758	Smoothing	Averaging of data in space or time, designed to compensate for random errors or fluctuations of a scale smaller than that presumed significant to a specific problem. [14]
1759	Sonargram	The analog echo record produced by the side scan sonar recording device on special chemically-treated paper. [14]
1760	Sono-Buoy	A buoy with equipment for automatically transmitting a radio signal when triggered by an underwater sound signal. [14]
1761	Spar Buoy	A buoy made of a tapered log or metal shaped like a tapered log, and secured so as to float in an approximately vertical position. [14]
1762	Split Fix	See fix. [14]
1763	Standpipe	A tall cylindrical structure in a waterworks system, whose height is several times greater than its diameter. It extends from the ground and may be supported by a skeleton-type framework. [14]
1764	Steradian	The unit of a solid angle in the si system. [14]
1765	Stippling	Graduation of shading by numerous separate touches. Shallow areas on charts, for instance, are sometimes indicated by numerous dots decreasing in density as the depth increases. [14]
1766	Sun: Mean	A fictitious sun conceived to move eastward along the celestial equator at a rate that provides a uniform measure of time equal to the average apparent time. It is used as a reference for reckoning mean time, zone time, etc. [14]
1767	Sun: True	See sun: apparent. [14]
1768	Tableland	An elevated region of land with a generally level surface of large or considerable extent; a lofty plain; a plateau. [14]
1769	Tail Wind	Wind which blows in the same direction as that in which an object is moving, with respect to the earth's surface. [14]
1770	Tectonics	The study of origin and development of the broad structural features of the earth. [14]
1771	Telemetry	The study and technique involved in measuring a quantity or quantities in place, transmitting this value to a station, and there interpreting, indicating, or recording the quantities; and transmitting commands from the station to control the measurement device. [14]
1772	Telemotor	A hydraulic or electrical device controlling the action of power at a distance, specifically, a device which controls the steering gear of a ship. [14]
1773	Tide Gate	A restricted passage through which water runs with great speed due to tidal action. [14]
1774	Tide Race	A strong tidal current or a channel in which such a current flows. [14]
1775	Tide: Ebb	See tide: falling. [14]
1776	Tide: Low	See low water. [14]
1777	Tie Point	Point of closure of a survey either on itself or on another survey. [14]
1778	Time Ball	A visual time signal in the form of a ball. [14]
1779	Time Zone	See zone. [14]
1780	Tolerance	The maximum allowable variation from a standard or from specified conditions. [14]
1781	True Wind	Wind vector in relation to the earth's surface. For a moving object it is the vector sum of the relative wind and the velocity of the object. [14]
1782	Tuff-Cone	See tuff. [14]
1783	Turbidite	Turbidity current deposits, characterized by both vertically and horizontally graded bedding. [14]
1784	Turbidity	Reduced water clarity resulting from the presence of suspended matter. Water is considered turbid when its load of suspended matter is visibly conspicuous, but all waters contain some suspended matter and therefore are turbid. Reduced transparency of the atmosphere, caused by absorption and scattering of radiation by solid or liquid particles, other than clouds, held there in suspension. [14]
1785	Type Face	A type of print, such as roman, egyptian, caslon, etc. [14]
1786	Uncovered	(Adj.). Above water. The opposite is submerged. [14]
1787	Warm Pool	A body of warm water entirely surrounded by cold water. [14]
1788	Water Sky	Typical dark patches and strips on low clouds over a water area enclosed in ice or behind its edge. [14]
1789	Waterline	The line marking the junction of land and water. The line along which the surface of the water touches a vessel's hull. Also written as two words. [14]
1790	Wave Base	The greatest depth at which sediment on the sea floor can just be stirred by the oscillating water. [14]
1791	Wavemeter	An instrument for measuring waves. One used for ocean waves usually measures height and period; one used for electromagnetic or sound waves usually measures length. Also written as two words. [14]
1792	Whirlpool	Water in rapid rotary motion. See eddy. [14]
1793	Whirlwind	General term for a small-scale rotating column of air. [14]
1794	Wind Farm	a collection of wind turbines that are collocated and are organized as a single power generation unit. [14]
1795	Wind Vane	An instrument used to indicate wind direction. [1]
1796	Air Camera	A camera specially designed for use in flying craft. [14]
1797	Alkalinity	The number of milliequivalents of hydrogen ions that are neutralized by 1 kilogram of sea water at 20°c when a large excess of acid is added. [14]
1798	Anemometer	Instrument used in the measurement of wind speed or of wind speed and direction. See also anemograph. [14]
1799	Annotation	Any marking on illustrative material for the purpose of clarification, such as numbers, letters, symbols, and signs. [14]
1800	Antiselena	Luminous phenomenon analogous to anthelion, the luminary being the moon. [14]
1801	Anti-Trade	Air current with a westerly component which in various subtropical regions of either hemisphere sometimes blows above the trade wind. [14]
1802	Astrometry	That branch of astronomy dealing with the determination of positions and motions of celestial bodies, including the earth. [14]
1803	Automation	The technique of improving human productivity in the processing of materials, energy and information, by utilizing in various degrees elements of automatic control, and of automatically executed product programming. [14]
1804	Bathymeter	An instrument primarily designed for measuring depth of water. [14]
1805	Beam Width	The angular measure of the transverse section of a beam (usually in the main lobe) lying within directions corresponding to specified values of field strength relative to the maximum. [14]
1806	Bold Coast	A prominent land mass that rises steeply from the sea. [14]
1807	Borderland	A region adjacent to a continent, normally occupied by or bordering a shelf and sometimes emerging as islands, that is irregular or blocky in plan or profile, with depths well in excess of those typical of a shelf. [14]
1808	Bottom Ice	See anchor ice. [14]
1809	Buoy: Life	A buoy intended to keep persons afloat. Also called life jacket. [14]
1810	Cable Buoy	See buoy. [14]
1811	Cable Sign	A sign on a post marking the point from which a cable runs under water. [14]
1812	Calcareous	(adj). Composed of or containing calcium or calcium carbonate. [14]
1813	Calculator	A machine for performing arithmetical operations usually more complex than that done by an adding machine; a calculating machine, which may be mechanical, electrical, electronic or a combination of all three. A person who calculates. [14]
1814	Cavitation	The turbulent formation, generally mechanically induced, including growth and collapse of bubbles in a fluid, and occurring when the static pressure at any point in fluid flow is less than fluid vapor pressure. [14]
1815	Cgs System	See centimeter-gram-second (cgs) system. [14]
1816	Chart: New	The first publication of a chart. [14]
1817	Chlorosity	The property of sea water corresponding to the chlorinity expressed as grams per litre at 20°. [14]
1818	Choppy Sea	The state of the sea caused by interaction of waves running in different directions. [14]
1819	Civil Time	See time. [14]
1820	Civil Year	See year. [14]
1821	Colatitude	The complement of the latitude, or 90° minus the latitude. [14]
1822	Comparator	An instrument for measuring a dimension in terms of a standard. An optical instrument for measuring rectangular or polar coordinates of points on any plane surface, such as a photographic plate. [14]
1823	Conduction	The transfer of heat by molecular activity from one substance to another, or through a substance. Transfer is always from warmer to colder regions. [1]
1824	Confluence	Flowing together. The place where two or more rivers, streams, etc. Unite. In meteorology, progressive drawing together of the streamlines in the direction of flow. [14]
1825	Contouring	The process of establishing lines representing equal values of a quantity on a map or chart. [14]
1826	Coral Head	A massive mushroom or pillar shaped coral growth. [14]
1827	Cordillera	A range or system of mountains. [14]
1828	Covariance	The arithmetic mean or expected value of the product of the deviations of corresponding values of two variables from their respective mean values. [14]
1829	Cross Wind	Wind which blows in a direction perpendicular to that of the motion of a moving object, relative to the earth's surface. [14]
1830	Crosslines	Sounding lines that cross the main system of lines at either right angles or at an oblique angle to serve as a check on the accuracy of the work. [14]
1831	Dark Slide	See slide: dark. [14]
1832	Day: Civil	A mean solar day beginning at midnight. [14]
1833	Day: Lunar	The duration of one rotation of the earth on its axis, with respect to the moon. Its average length is about 24h50m of mean solar time. Also called tidal day. The duration of one rotation of the moon on its axis, with respect to the sun. [14]
1834	Day: Tidal	See day: lunar and tidal day. [14]
1835	Dead Ahead	Bearing 000° relative. If the bearing is approximate, the term ahead should be used. [14]
1836	Dead Water	The phenomenon which occurs when a ship of low propulsive power negotiates water which has a thin layer of fresher water over a deeper layer of more saline water. As the ship moves, part of its energy goes into generation of an internal wave which causes a noticeable drop in efficiency of propulsion. [14]
1837	Diagenesis	The chemical and physical changes that sediments undergo after their deposition, by lithification. [14]
1838	Dispersion	The separation of radiant energy into its various components. In optics, the separation of light into its component colors by its passage through a diffraction grating or by refraction such as that provided by a prism. In oceanography, the separation of a complex surface gravity wave disturbance into its component parts. [14]
1839	Divider(S)	Measuring compasses having both legs pointed, used principally for measuring distances and coordinates. [14]
1840	Drift Buoy	A data collection buoy which is not moored to the sea bottom, but drifting freely in response to currents, tides, and wind. [14]
1841	Drift Lead	See lead. [14]
1842	Earth Tide	See tide. [14]
1843	Exit Pupil	The image of aperture stop formed by all the lens elements on the image side of the aperture stop. [14]
1844	Fair Sheet	See fair chart. [14]
1845	Fix: Split	A fix obtained by measuring two angles to four objects whose positions are known, i.e. With no common center object. [14]
1846	Float Well	A vertical pipe or box with a relatively small opening in the bottom, used to enclose the float of a tide gauge so the float will be little affected by nontidal motions of the water. Synonymous with stilling well. [14]
1847	Form Lines	Lines drawn to represent the shape of terrain; unlike contour lines, these are drawn without regard to a true vertical datum or regular vertical interval. [14]
1848	Foul Berth	A berth in which a vessel cannot swing to her anchor or moorings without fouling another vessel or striking an obstruction. [14]
1849	Geophysics	The study of the physical characteristics and properties of the earth. [14]
1850	Glaciology	The study of snow and ice on the earth's surface, with specific concentration on the regime of active glaciers. [14]
1851	Gold Slide	An adjustable attachment to a mercurial barometer for giving resultant of corrections for index error, height of instrument above sea level, variation in gravity due to latitude, temperature. Invented by col. E. Gold. [14]
1852	Goniometer	An instrument for measuring angles. A pick-up coil which eliminates the necessity of having to rotate a radio direction finder antenna to determine direction. [14]
1853	Gravimeter	A weighing device or instrument of sufficient sensitivity to register variations in the weight of a constant mass when the mass is moved from place to place on the earth and thereby subjected to the influence of gravity at those places. Also called gravity meter. [14]
1854	Grid Ticks	Short lines indicating where selected grid lines intersect the neat line. [14]
1855	Ground Ice	See anchor ice. [14]
1856	Ground Log	See log. [14]
1857	Guard Lock	See tide lock. [14]
1858	Gyro Pilot	An automatic pilot controlled by gyroscopes. An automatic device for steering a vessel by means of control signals from a gyroscopic compass. [14]
1859	Hinterland	The district behind that lying along the coast; the back country. [14]
1860	Hummocking	Pressure process by which level ice becomes broken up into hummocks. [14]
1861	Hydrometer	An instrument for determining the specific gravity of liquids. [14]
1862	Hygrometer	An instrument for measuring the humidity of the air. See also psychrometer. [14]
1863	Hypsometry	The determination of elevations above sea level. Generally applied to the determination of eleva-tions through the measurement of air pressure by observing the boiling point of a liquid. [14]
1864	Hysteresis	Retardation or lag in the effect of changing forces, as in ship's magnetism induced by the earth's magnetic field. [14]
1865	Ice Nuclei	Particles that act as nuclei for the formation of ice crystals in the atmosphere. [1]
1866	Infrasonic	(Adj.). Having a frequency below the audible range. [14]
1867	Insolation	Amount of direct solar radiation incident per unit horizontal area at a given level. Downward-directed solar radiation (global radiation). [14]
1868	Invar Tape	See tape. [14]
1869	Invar Wire	See wire. [14]
1870	Isodynamic	(Adj.). Of or pertaining to equality of force. [14]
1871	Isohalsine	See isohaline. [14]
1872	Jet Streak	A region of high wind speed that moves through the axis of a jet stream. Also called jet maximum. [1]
1873	Kite Otter	A multi-plane device which can be used either as a kite or as an otter depending on the way it is slung. See oropesa sweep. [14]
1874	Kymatology	The science of waves and wave motion. [14]
1875	Lead (Led)	A navigable passage through ice. The amount one cyclic motion is ahead of another, expressed in degrees. [14]
1876	Lead: Fish	A fish-shaped sounding lead which reduces to a minimum the inclination of the wire when trailed, making unnecessary its removal from the water between soundings. [14]
1877	Lead: Hand	A light sounding lead (3 to 5 kilos) having usually a line of not more than 40 to 50 meters. [14]
1878	Light-Year	A unit of length equal to the distance light travels in one year. This unit is used as a measure of stellar distance. [14]
1879	Lunar Tide	See under tide. [14]
1880	Macroscale	The normal meteorological synoptic scale for obtaining weather information. It can cover an area ranging from the size of a continent to the entire globe. [1]
1881	Making Way	Progressing through the water. [14]
1882	Map: Index	In aerial photography, a map showing the location and numbers of flight strips and photographs. [14]
1883	Microburst	A strong localized downdraft (downburst) less than 4 km wide that occurs beneath thunderstorms. A strong downburst greater than 4 km across is called a macroburst. [1]
1884	Microphone	An electroacoustic device containing a transducer which is actuated by sound waves and delivers essentially equivalent electric waves. [14]
1885	Microscale	The smallest scale of atmospheric motions. [1]
1886	Mixed Seas	The state of the sea resulting from the interaction of wind, waves, and swell. [14]
1887	Mixed Tide	See tide. [14]
1888	Mobile Rig	See rig. [14]
1889	Mock Moons	Name given sometimes to paraselenae, parantiselenae and antiselenae when they are bright. [14]
1890	Monitoring	Checking of the operation and performance of an electronic system through reception of its signals. [14]
1891	Nadir: Map	The map position for the ground nadir. [14]
1892	Nanosecond	A thousand millionth of a second. [14]
1893	Nautophone	A horn having a diaphragm oscillated by electricity. [14]
1894	New Survey	See resurvey. [14]
1895	Niggerhead	Large blocks of coral torn loose from the outer face of a reef and tossed on to the reef flat by storm waves or tsunamis. The blocks are blackened by a crust of lichens after detachment from the reef. [14]
1896	Noon: Mean	Twelve o'clock mean time. [14]
1897	Ocean Eddy	A moving or stationary local rotating formation where water predominantly moves along circular paths. [14]
1898	Open Sound	A bay similar to a lagoon but with large openings between the protecting islands. [14]
1899	Open Water	A relatively large area of free navigable water in an ice-encumbered sea. In US Terminology, an area of sea with less than one-tenth ice concentration. [14]
1900	Opisometer	A recording device designed to measure by revolutions of a small wheel, continuous linear distances on a map. Used in measuring the length of shoreline by closely following all the indentations and sinuosity’s of the shore. [14]
1901	Outgassing	The release of gases dissolved in hot, molten rock. [1]
1902	Ozone (O3)	An almost colorless gaseous form of oxygen with an odor similar to weak chlorine. The highest natural concentration is found in the stratosphere where it is known as stratospheric ozone. It also forms in polluted air near the surface where it is the main ingredient of photochemical smog. Here, it is called tropospheric ozone. [1]
1903	Ozone (O3)	An almost colorless gaseous form of oxygen with an odor similar to weak chlorine. The highest natural concentration is found in the stratosphere where it is known as stratospheric ozone. It also forms in polluted air near the surface where it is the main ingredient of photochemical smog. Here, it is called tropospheric ozone. [1]
1904	Ozone Hole	A sharp drop in stratospheric ozone concentration observed over the Antarctic during the spring. [1]
1905	Pantograph	An instrument for copying a chart, drawing, etc., to any desired scale within the limits of the instrument. [14]
1906	Paraselene	Optical phenomenon of the halo family, similar to but less brilliant than the parhelion, the luminary being the moon. [14]
1907	Pass Point	In photogrammetry, a point whose horizontal and/or vertical position is determined from photo-graphs by photogrammetrically methods and which is intended for use (as in the manner of a supplemental control point) in the orientation of other photographs. [14]
1908	Passometer	A pocket-size instrument which registers the number of steps taken by the pedestrian carrying it. See pedometer. [14]
1909	Phonometer	An instrument for measuring the intensity or frequency of sounds. [14]
1910	Photo Base	The length of the air base as represented on a photograph. [14]
1911	Photoindex	A mosaic made by assembling individual photographs, with accompanying designations, into their proper relative positions and copying the assembly photographically at a reduced scale. [14]
1912	Photometer	An instrument used in measuring the intensity of light, especially in determining the relative intensity of different lights. [14]
1913	Piggot Gun	A coring instrument for obtaining deep-sea bottom samples. This instrument uses an explosive charge to drive a metal bit into the bottom at the instant the sharp end of the bit strikes the bottom. [14]
1914	Planimeter	A mechanical integrator for measuring the area of a plane surface. [14]
1915	Planimetry	The measurement of plane surfaces. The plan details of a map. [14]
1916	Promontory	A high point of land extending into a body of water. A cape. [14]
1917	Pycnocline	A vertical positive density gradient in some layer of a body of water, which is appreciably greater than gradients above and below it. [14]
1918	Radar Buoy	See buoy. [14]
1919	Radar Dome	A dome shaped structure used to protect the antenna of a radar installation. [14]
1920	Radar Line	See radar guided track. [14]
1921	Radar View	A depiction (photographic reproduction or drawing) of appearance of landmarks on the ppi scope of a radar set at a particular geographic location, intended to facilitate the identification of the coast. This can aid the navigator to identify or match his own radar image of these same landmarks. [14]
1922	Radarsonde	Equipment used for determining high-level winds, by means of radar aimed at a target carried by a free balloon. [14]
1923	Radio Aids	An aid to navigation transmitting information by radio waves. [14]
1924	Radio Mast	A tower, pole, or other structure for elevating an antenna. [14]
1925	Radiometer	An instrument for measuring the intensity of radiant energy. [14]
1926	Real Image	See image. [14]
1927	Region A,B	Within the iala maritime buoyage system there are two international buoyage regions, designated as region a and region b, where lateral marks differ only in the colors of port and starboard hand marks. [14]
1928	Relief Map	See map. [14]
1929	Right Bank	Of a river, the bank on the right-hand side as one proceeds downstream. [14]
1930	Rock Borer	A member of any of several families of bivalves that live in cavities they bore in soft rock, concrete and other material. [14]
1931	Rock Flour	Finely ground rock particles, chiefly silt size, resulting from glacial abrasion. A component of marine deposits off glacial stream mouths. [14]
1932	Rocky Area	An area with a rocky bottom. [14]
1933	Rod: Range	See range rod. [14]
1934	Roll Cloud	A dense, roll-shaped, elongated cloud that appears to slowly spin about a horizontal axis behind the leading edge of a thunderstorm's gust front. [1]
1935	Rotten Ice	Sea ice which has become honeycombed in the course of melting, and which is in an advanced state of disintegration. [14]
1936	Salt Marsh	Flat, poorly drained coastal swamps which are flooded by most high tides. [14]
1937	Sea Valley	See valley. [14]
1938	Seamanship	A general term for the art by which vessels are handled. [14]
1939	Shadow Pin	A small rod or pin used to cast a shadow on an instrument, such as a magnetic compass or sun com-pass, to determine the direction of the luminary; a gnomon. [14]
1940	Shore Lead	A lead between pack ice and the shore, or between pack ice and a narrow fringe of fast ice. [14]
1941	Sill Depth	The greatest depth over a sill. [14]
1942	Sketch Map	See map. [14]
1943	Solar Apex	See apex. [14]
1944	Solar Cell	A cell using the solar light or other light energy for conversion into electric energy. [14]
1945	Solar Tide	See tide. [14]
1946	Sonic Boom	A loud explosive-like sound caused by a shock wave emanating from an aircraft (or any object) traveling at or above the speed of sound. [1]
1947	Stadimeter	An instrument used to measure the distance from the observer to a more-or-less distant object, such as a vessel, when the height of a specified part of the latter (e.g. The mast) is known. It is in effect a hand-held range finder. [14]
1948	Star Chart	See chart. [14]
1949	Statoscope	A highly sensitive barometer or altimeter for measuring slight variations in pressure or altitude. [14]
1950	Stereogram	A stereoscopic pair of photographs or drawings correctly oriented and mounted or projected for stereoscopic viewing. [14]
1951	Sun Pillar	A vertical streak of light extending above (or below) the sun. It is produced by the reflection of sunlight off ice crystals. [1]
1952	Supersonic	(Adj.). Designating or of a speed greater than the speed of sound. [14]
1953	Swash Mark	The thin wavy line of fine sand, mica scales, bits of seaweed, etc., left by the uprush when it recedes from its upward limit of movement on the beach. [14]
1954	Swept Area	An area that has been determined to be clear of navigational dangers to a specified depth [14]
1955	Tablemount	A seamount having a comparatively smooth flat top. Also called guyot. [14]
1956	Tabulation	Orderly arrangement as in a table. [14]
1957	Tachometer	A device that indicates or measures the revolutions per minute of a revolving shaft or the velocity of a machine. [14]
1958	Tape: Base	See base tape (or wire). [14]
1959	Thermogram	Record made by a thermograph. [14]
1960	Tidal Bore	See bore. [14]
1961	Tidal Flat	A marsh or sandy or muddy coastal flatland which is covered and uncovered by the rise and fall of the tide. [14]
1962	Tide Bulge	See tide wave. [14]
1963	Tide Crack	The fissure at the line of junction between an immovable icefoot or ice wall and fast ice, the latter being subject to the rise and fall of the tide. [14]
1964	Tide Curve	Any graphic representation of the rise and fall of the tide. Time is generally represented by the abscissae and the height of the tide by ordinates. For normal tides the curve so produced approximates a sine curve. Also called marigram. [14]
1965	Tide: Half	The condition or time of the tide when at the level midway between any given high tide and the following or preceding low tide. [14]
1966	Tide: High	See high water. [14]
1967	Tide-Bound	(Adj.). Unable to proceed because of insufficient depth of water due to tidal action. [14]
1968	Tilt: Base	In photogrammetry, the inclination of the air base with respect to the horizontal. [14]
1969	Time: Zone	The local mean time of a reference or zone meridian, whose time is kept throughout a designated zone. The zone meridian is usually the nearest meridian whose longitude is exactly divisible by 15°. [14]
1970	Trajectory	The curved path of something hurtling through space. In meteorology, curve traced by the successive positions of a moving particle of air. Curve traced by the successive positions of the center of a selected synoptic system, such as a depression. In oceanography, the path followed by moving water particles. In electronics the path followed by electrons emanating from the cathode as in an electron tube. [14]
1971	Undercliff	A terrace or lower cliff formed by a landslide. Also written as two words. [14]
1972	Upper Limb	See limb. [14]
1973	Vectograph	A stereoscopic photograph composed of two superimposed images which polarize light in planes 90° apart. When these images are viewed through polaroid spectacles with the polarization axes at right angles, an impression of depth is obtained. [14]
1974	Vignetting	In photography, a gradual reduction in density of parts of a photographic image due to the stopping of some of the rays entering the lens. [14]
1975	Waterspout	A column of rotating wind over water that has characteristics of a dust devil and a tornado. [1]
1976	Wave Setup	The result of 'sets' of waves transporting water shoreward and raising the sea level. [16]
1977	Wave: Edge	An ocean wave travelling parallel to a coast, with crests normal to the coastline. Such a wave has a height that diminishes rapidly seaward and is negligible at a distance of one wavelength offshore. [14]
1978	Wave: Free	A wave that continues to exist after the generating force has ceased to act, in contrast with a forced wave that is generated and maintained by a continuous force. A free wave on a water surface is one created by a sudden impulse, thereafter influenced only by friction, the dimensions of the basin, and the dispersive character of the water medium it moves in. Most ocean surface waves except tidal waves are free waves. See oscillation. [14]
1979	Wave: Tide	See tide. [14]
1980	Wave: Wind	A wave resulting from the action of wind on a water surface. See fetch. [14]
1981	Winter Ice	More or less unbroken, level sea ice of not more than one winter's growth originating from young ice. Thickness from 15 cm to 2 m. [14]
1982	Wire: Base	See base tape (or wire). [14]
1983	Wreck Buoy	A buoy marking the location of a wreck. [14]
1984	Xerography	A process of electrostatic printing which employs a special selenium-coated plate, useable many times over. [14]
1985	Xerophytes	Drought-resistant vegetation. [1]
1986	Abyssal Gap	A gap in a sill, ridge, or rise that lies between two abyssal plains. [14]
1987	Aggradation	See accretion. [14]
1988	Agonic Line	The line through all points on the earth's surface at which the magnetic variation is zero. [14]
1989	Air Almanac	See under almanac. [14]
1990	Amici Prism	A prism which deviates the rays of light through 90° and because of its shape inverts the image. See roof prism. [14]
1991	Anchor Buoy	A buoy marking the position of an anchor. [14]
1992	Angle: Hour	See hour angle. [14]
1993	Antipode(S)	Place(s) on the surface of the earth directly opposite to each other. [14]
1994	Apex: Solar	The point of the celestial sphere towards which the solar system as a whole is moving. It lies in the constellation of Hercules. [14]
1995	Aquaculture	The cultivation of aquatic fauna and flora. [14]
1996	Axis: Polar	In a system of polar or spherical coordinates, the primary axis of direction. [14]
1997	Baroclinity	The condition and type of motion in which pressure is not constant on surfaces of constant density, e.g. Internal waves. [14]
1998	Barrel Buoy	See buoy. [14]
1999	Bathysphere	A diving sphere for deep-sea observations. [14]
2000	Box Sextant	A small portable instrument used for approximate measurement of angles. [14]
2001	Buoy: Cable	A buoy used to indicate the run of a submarine cable. [14]
2002	Buoy: Radar	A buoy with a cluster of radar reflectors. [14]
2003	Candlepower	Luminous intensity expressed in candelas. Also written as two words. [14]
2004	Chart Scale	See scale. [14]
2005	Chart: Fair	See fair chart. [14]
2006	Chart: Grid	A chart only showing a cartographic grid on its inner border. [14]
2007	Chart: Star	A representation, on a flat surface, of the celestial sphere or a part of it, showing the positions of the stars and sometimes other features of the celestial sphere. [14]
2008	Chlorophyll	The green pigment contained in the leaves of plants. See photosynthesis. [14]
2009	Chronograph	An instrument for measuring and recording time or time intervals. [14]
2010	Circle: Dip	See dip circle. [14]
2011	Climatology	Study of climates (causes, variations, distributions, types, etc.). [14]
2012	Coalescence	The merging of cloud droplets into a single larger droplet. [1]
2013	Coast Chart	See chart. [14]
2014	Contour Map	See map. [14]
2015	Core Sample	See core. [14]
2016	Cosmic Dust	Very fine particles of solid matter in any part of the universe, including meteoric dust and zodiacal light particles in the solar system, interstellar matter of uncertain origin in the milky way galaxy, and accumulation of dark matter in other galaxies. [14]
2017	Customhouse	The office, especially in harbors, at which customs are collected. [14]
2018	Danger Buoy	See isolated danger mark. [14]
2019	Danger Line	A line drawn on a chart, to indicate the limits of safe navigation for a vessel of specific draft. A dotted line on a chart to emphasize the presence of an obstruction. [14]
2020	Dart Leader	The discharge of electrons that proceeds intermittently toward the ground along the same ionized channel taken by the initial lightning stroke. [1]
2021	Dead Astern	Bearing 180° relative. If the bearing is approximate, the term astern should be used. Also called right astern. [14]
2022	Demagnetize	(v.t.). To remove magnetism. The opposite is magnetize. [14]
2023	Depth Gauge	See gauge. [14]
2024	Design Wave	Deterministic wave used for the design of an offshore structure. [14]
2025	Diapositive	A positive photograph on a transparent medium. One which has a right reading image when viewed through the base support. [14]
2026	Diffraction	The bending of the rays of radiant energy around the edges of an obstacle, or when passing near the edges of an opening, or through a small hole or slit, resulting in the formation of a spectrum, or arrangement by wavelength of component waves, producing, for visible wavelengths, the chromatic spectrum. The bending of a wave as it passes an obstruction. [14]
2027	Direct Wave	See wave. [14]
2028	Discrepancy	A difference between results of duplicate or comparable measures of a quantity. The difference in computed values of a quantity obtained by different processes using data from the same survey. [14]
2029	Dish Aerial	A parabolic aerial for the receipt and transmission of high frequency radio signals. [14]
2030	Dixie Alley	Region in the southern united states, typically over mississippi and alabama, where tornadoes often form. [1]
2031	Double Tide	See tide. [14]
2032	Draft Marks	Numerals at the bow and stern of a vessel that indicate the depth to which the vessel is submerged. [14]
2033	Draughtsman	See draftsman. [14]
2034	Driver Tube	See driver rod. [14]
2035	Drying Line	The line marking the transit from water to land; usually the low-water line. [14]
2036	Duck Blinds	Non floating structures used for concealing waterfowl hunters. They usually consist of a wooden framework covered with brush. They are essentially unreported to any charting authority when built. They are unlighted and often constructed in navigable water without regard to the possible hazard they pose, especially to the small craft operator. Many are substantial structures built on piles. Even after they are eventually reduced to ruins the pilings may persist for years. [14]
2037	Dx90-Format	Format for supply or interchange of digital cartographic data. Dx90 provides two modes: the sequential, and the chain mode. [14]
2038	Dynamometer	An apparatus for measuring force or energy. [14]
2039	Earth Light	Feeble light of the dark part of the moon's disc produced by the solar light reflected by the earth including the atmosphere. Also written as one word. Also called earthshine. [14]
2040	Electrotape	A trade name for a precise electronic distance measuring device operating on the same principle as the tellurometer. Originally designated as micro-dist. [14]
2041	Erect Image	See image. [14]
2042	Exit Window	The image of the field stop formed by all the lens elements on the image side of the field stop. [14]
2043	Field Chart	See chart. [14]
2044	Field Sheet	The hydrographer's or topographer's work sheet; it presents a graphic display of all surface and subsurface features in the area being surveyed. See also boat sheet. [14]
2045	Flare Stack	A tall structure used for burning-off waste oil or gas. [14]
2046	Flash Flood	A flood that rises and falls quite rapidly with little or no advance warning, usually as the result of intense rainfall over a relatively small area. [1]
2047	Float Gauge	See gauge. [14]
2048	Focal Point	See focus. [14]
2049	Fog Patches	Fog in banks irregularly distributed. [14]
2050	Fog Trumpet	A trumpet used as a fog signal. [14]
2051	Fog Whistle	A whistle used as a fog signal. [14]
2052	Forced Wave	See wave. [14]
2053	Forward Lap	See overlap. [14]
2054	Foul Bottom	A hard, uneven, rocky or obstructed bottom having poor holding qualities for anchors, or one having rocks or wreckage that would endanger an anchored vessel. [14]
2055	Foul Ground	An area over which it is safe to navigate but which should be avoided for anchoring, taking the ground or ground fishing. [14]
2056	Frost Smoke	Fog-like clouds, due to the contact of cold air with relatively warm sea water, which appear over newly formed leads and pools, or leeward, of the ice edge, and which may persist while slush or sludge and young ice are forming. [14]
2057	Gauge: Rain	Instrument for measuring the depth of water from precipitation supposed distributed over a hori-zontal impervious surface and not subject to evaporation. Also written as one word. [14]
2058	Glacier Ice	Any ice floating on the sea as an iceberg, which originates from a land glacier. Also called land ice. [14]
2059	Green Flash	A small green color that occasionally appears on the upper part of the sun as it rises or sets. [1]
2060	Grid Course	See course. [14]
2061	Gross Error	See error. [14]
2062	Gulf Stream	A warm, swift, narrow ocean current flowing along the east coast of the united states. [1]
2063	Hadley Cell	A thermal circulation proposed by George Hadley to explain the movement of the trade winds. It consists of rising air near the equator and sinking air near 30° latitude. [1]
2064	Hard Bottom	The sea floor not covered by unconsolidated sediment. [14]
2065	Heat Stroke	A physical condition induced by a person's overexposure to high air temperatures, especially when accompanied by high humidity. [1]
2066	Hindcasting	Method of simulating historical (metocean) data for a region through numerical modelling [14]
2067	Hydrometeor	Meteor consisting of an ensemble of liquid or solid water particles falling through or suspended in the atmosphere, blown by the wind from the earth's surface or deposited on objects on the ground or in the free air. [14]
2068	Hypothermia	The deterioration in one's mental and physical condition brought on by a rapid lowering of human body temperature. [1]
2069	Ice Cluster	A concentration of sea ice covering hundreds of square kilometers, which is found in the same region every summer. [14]
2070	Image: Real	An image actually produced and capable of being shown on a surface, as in a camera. [14]
2071	Indentation	A recess in a coastline. [14]
2072	Index Chart	See chart. [14]
2073	Index Shade	On a sextant, one of the pivoting coloured glasses which can be swung before the index mirror for reducing the glare of the sun. [14]
2074	Iridescence	Brilliant spots or borders of colors, most often red and green, observed in clouds up to about 30° from the sun. [1]
2075	Jack-Up Rig	A rig which provides a stable drilling structure in shallow waters by extending supporting legs onto the seabed. The legs are retracted when the rig is under tow. [14]
2076	Kelvin Wave	A long ocean wave whose amplitude decreases from right to left along the wave crest when viewed in the direction of travel in the northern hemisphere and from left to right in the southern hemisphere. The component of gravity acting down the slope is exactly balanced by the deflecting force of the earth's rotation, the Coriolis force. [14]
2077	Lake Breeze	See sea breeze. [14]
2078	Latent Heat	The heat that is either released or absorbed by a unit mass of a substance when it undergoes a change of state, such as during evaporation, condensation, or sublimation. [1]
2079	Lead (Lã¨D)	A heavy, soft, malleable, bluish-grey metallic chemical element. Anything made of this metal, such as a weight for sounding depths of water. [14]
2080	Lead: Drift	Sounding lead dropped to bottom, to indicate movement of a vessel. [14]
2081	Least Count	The finest reading that can be made directly (without estimation) from a vernier or micrometer. [14]
2082	Light Float	A boat-like structure used instead of a light buoy in waters where strong streams or currents are experienced, or when a greater elevation than that of a light buoy is necessary. [14]
2083	Light: Rear	See light(s): range. [14]
2084	Line Squall	Squall which occurs along a squall line. [14]
2085	Lithosphere	The solid, rocky part of the earth; earth's crust distinguished from atmosphere, hydrosphere. [14]
2086	Log: Ground	A device for determining the course and speed made good over the ground in shallow water, consisting of a lead attached to a line. The lead is thrown overboard and allowed to rest on the bottom. The course being made good is indicated by the direction the line tends and the speed by the amount of line paid out in unit time. [14]
2087	Log: Patent	Former name for a towed log. Any mechanical log, particularly a taffrail log. [14]
2088	Magnetogram	An analogue time record of the temporal variations in a magnetic element measured at a magnetic observatory. [14]
2089	Map: Relief	A map emphasizing relief or relative elevations. See relief model. [14]
2090	Map: Sketch	A map drawn freehand and greatly simplified which, although preserving the essential space relationships, does not truly preserve scale or orientation. [14]
2091	Marine Farm	See fish farm. [14]
2092	Mesoclimate	The climate of an area ranging in size from a few acres to several square kilometers. [1]
2093	Meter Wheel	A special block used to measure paid out sampling line at oceanographic stations. [14]
2094	Microsecond	One millionth of a second. [14]
2095	Microseisms	More or less persistent feeble earth tremors caused by natural sources such as atmospheric pressure systems or waves. [14]
2096	Mixed Layer	In oceanography, the surface layer of virtually isothermal water, which frequently exists above the thermocline. The thickness of the layer is dependent on the temperature gradient. [14]
2097	Mud Snapper	See snapper. [14]
2098	North: Grid	An arbitrary reference direction used with grid navigation. The northerly or zero direction indicated by the grid datum of directional reference. [14]
2099	North: True	The direction of the north geographic pole. [14]
2100	Omnibearing	The magnetic bearing of an omnirange. [14]
2101	Opalescence	Whitish colour of the atmosphere and a slight change of the apparent colour of objects with respect to normal (for example, bluish colour of an object normally black or dark) produced by the scattering of light by small particles held in suspension in the atmosphere. [14]
2102	Overrunning	A condition that occurs when air moves up and over another layer of air. [1]
2103	Oxygen (O2)	A colorless and odorless gas that occupies about 21 percent of dry air in the lower atmosphere. [1]
2104	Pacific Air	Cool, moist air that originates over the Pacific Ocean, moves eastward, then descends the rocky mountains and moves over the plains as dry, stable, relatively cool air. [1]
2105	Pancake Ice	Pieces of new ice, usually approximately circular, about 30 cm to 3 m across, and with raised rims, due to the pieces striking against each other as the result of wind and swell. [14]
2106	Pecked Line	In cartography, a symbol consisting of a line broken at regular intervals. [14]
2107	Pencil Beam	A beam in which the radiant energy is concentrated in an approximately conical or cylindrical portion of space of relatively small diameter. This type beam is used for many revolving navigational lights. [14]
2108	Percolation	The process by which water is forced by wave action through the interstices of the bottom sediment and has a tendency to reduce wave heights. [14]
2109	Photosphere	The visible surface of the sun and direct source of almost all its radiation. It is a gaseous layer some 400 km thick, below which the sun becomes opaque. [14]
2110	Pillar Buoy	A buoy composed of a tall central structure on a broad flat base. [14]
2111	Pilot Chart	See chart. [14]
2112	Pivot Point	After a ship has assumed its drift angle in a turn, the point on the centerline between the bow and the center of gravity at which the resultant of the velocities of rotation and transaction is directed along the centerline. To an observer on board, the ship appears to rotate about this point. [14]
2113	Plate Level	See level. [14]
2114	Pluviograph	Rain gauge which includes an arrangement for the time recording of the depth of water from precipitation. [14]
2115	Polar Chart	See chart. [14]
2116	Press Proof	A lithographed impression taken from among the first copies run on the press and used for checking purposes. Also called press pull. [14]
2117	Print: Blue	A nonreproducible blue image or outline usually printed photographically on paper. [14]
2118	Pseudorange	The time shift required to align (correlate) a replica of the gps code generated in the receiver with the received gps code, scaled into distance by the speed of light. This time shift is the difference between the time of signal reception (measured in the receiver time frame) and the time of emission (measured in the satellite time frame). [14]
2119	Qtg Station	A radio station which is prepared to provide qtg service, that is to say, to transmit upon request from a ship, a radio signal, the bearing of which can be taken by that ship. [14]
2120	Radar Chain	An arrangement of radar sets in a chain usually used for vessel traffic control. [14]
2121	Radar Chart	See chart. [14]
2122	Rain Shadow	The region on the leeside of a mountain where the precipitation is noticeably less than on the windward side. [1]
2123	Ratio Print	See print. [14]
2124	Reflectance	The ratio of light given off by an object to the amount of light striking the object, expressed as percentage. [14]
2125	Rift Valley	See median valley. [14]
2126	Ripple Mark	Undulating surface features of various shapes produced in unconsolidated sediments by wave or current action. [14]
2127	River Mouth	The exit or point of discharge of a river into the sea, a lake, or another river. [14]
2128	Running Fix	See fix. [14]
2129	Safety Aids	See aid to navigation. [14]
2130	Salinometer	Any device or instrument for determining salinity, especially one based on electrical conductivity methods. [14]
2131	Sea Channel	A continuously sloping elongated discrete depression commonly found in fans or abyssal plains and customarily bordered by levees on one or both sides. [14]
2132	Seismograph	An instrument that records the direction, intensity and time of earthquakes. [14]
2133	Selectivity	The degree of decrease in the response of a resonant device with departure from resonance. Selec-tivity determines the ability of a radio receiver to differentiate between signals of different carrier frequency. [14]
2134	Sexagesimal	An angular division whereby a circle is divided in 360 equal parts called degrees. A degree is divided in 60 minutes and one minute in 60 seconds. [14]
2135	Shade Glass	See shade. [14]
2136	Shadow Zone	A region into which very little sound energy penetrates. [14]
2137	Shelf Break	See shelf edge. [14]
2138	Shelf Cloud	A dense, arch-shaped, ominous-looking cloud that often forms along the leading edge of a thunderstorm's gust front, especially when stable air rises up and over cooler air at the surface. Also called an arcus cloud. [1]
2139	Signal: Fog	See fog signal. [14]
2140	Sky Compass	See compass. [14]
2141	Slide: Dark	A thin plate (usually metal or fibre, rigid or flexible) which, after insertion in a camera magazine, renders it light-tight. [14]
2142	Snow Grains	Precipitation in the form of very small, opaque grains of ice. The solid equivalent of drizzle. [1]
2143	Speed Scale	See scale. [14]
2144	Spoil Banks	Submerged accumulations of dumped material dredged from channels or harbors. [14]
2145	Squall Line	Fictitious moving line, sometimes of considerable extent, along which squall phenomena occur. [14]
2146	Steerageway	The condition wherein the ship has sufficient way on that it will respond to rudder movements to maintain desired course. [14]
2147	Stereometer	A measuring device comprising a micrometer movement by means of which the separation of two index marks can be changed to measure parallax difference on a stereoscopic pair of photographs. Also called parallax bar. [14]
2148	Stream: Ebb	See ebb stream. [14]
2149	Strong Gale	Wind with a speed between 41 and 47 knots (beaufort scale wind force 9). [14]
2150	Sun Compass	See compass. [14]
2151	Surface Map	A map that shows the distribution of sea-level pressure with isobars and weather phenomena. Also called a surface chart. [1]
2152	Survey Boat	A boat used for hydrographic surveys. [14]
2153	Survey Buoy	See buoy. [14]
2154	Survey Mark	An object placed at the site of a station to identify the surveyed location of that station. In particular, an object whose coordinates are used for control in a geodetic network. Also called marker, geodetic marker, and monument. [14]
2155	Survey: New	See resurvey. [14]
2156	Swirl Error	See error. [14]
2157	Tangent Arc	An arc of light tangent to a halo. It forms by refraction of light through ice crystals. [1]
2158	Terrigenous	(Adj.). Derived from the land. Applied to marine deposits, originating from the erosion of the land as opposed to pelagic deposits. [14]
2159	Texas Tower	A fixed tower mounted on the continental shelf or on a shoal, used to drill and operate gas or petroleum wells, and to provide a platform for aids to navigation and meteorological or oceanographic instrumentation. [14]
2160	Thermoprobe	A transducer used to measure temperature 'in situ' of ocean bottom sediments at depths beneath the bottom. Such measurements when combined with heat conductivity information provide a measurement of heat flow through the ocean bottom. [14]
2161	Tidal Basin	See basin. [14]
2162	Tidal Epoch	See phase lag. [14]
2163	Tidal Water	Any water the level of which changes periodically due to tidal action. See tidewater. [14]
2164	Tide Rip(S)	Small waves formed on the surface of water by the meeting of opposing tidal currents or by a tidal current crossing an irregular bottom. Vertical oscillation, rather than progressive waves, is charac-teristic of tide rips. [14]
2165	Tide Signal	See signal. [14]
2166	Tide: Earth	Periodic movement of the earth's crust caused by the tide-producing forces of the moon and sun. [14]
2167	Tide: Flood	See tide: rising. [14]
2168	Tide: Lunar	That part of the tide due solely to the tide-producing forces of the moon, as distinguished from that part caused by the forces of the sun. See tide: solar. [14]
2169	Tide: Mixed	The type of tide in which a diurnal wave produces large inequalities in heights and/or durations of successive high and/or low waters. This term applies to the tides intermediate to those predomi-nantly semidiurnal and those predominantly diurnal. [14]
2170	Tide: Slack	See slack water. [14]
2171	Tide: Solar	That part of the tide due solely to the tide-producing forces of the sun, as distinguished from that part caused by the forces of the moon. [14]
2172	Tide: Storm	See storm surge. [14]
2173	Time: Local	Time based upon the local meridian as reference, as contrasted with that based upon a zone meridian, or the meridian of Greenwich. Any time kept locally. [14]
2174	Time: Solar	Time based upon the rotation of the earth relative to the sun. See time: apparent solar, time: astronomical, time: civil, time: mean solar. [14]
2175	Torrid Zone	That part of the earth between the tropic of cancer and the tropic of Capricorn. Also called the tropics. [14]
2176	Track Chart	A chart showing recommended, required, or established tracks, and usually indicating turning points, courses, and distances. [14]
2177	Triangulate	The process of triangulation. [14]
2178	Trilaterate	The process of trilateration. [14]
2179	Ultrasonics	The science and technology relating to sound waves of frequencies above the audible range. [14]
2180	Upslope Fog	Fog formed as moist, stable air flows upward over a topographic barrier. [1]
2181	Vacuum Lead	A corer which makes use of hydrostatic pressure to force a tube into the bottom sediment. [14]
2182	Velocimeter	An instrument used for the 'in situ' measurement of the speed of sound in the sea and other natural waters. [14]
2183	Watch: Hack	A watch used for timing observations of celestial bodies regulating ship's clocks, etc. [14]
2184	Watch: Stop	A watch that can be started, stopped, and reset at will, to indicate elapsed time. [14]
2185	Water Front	Land at the end of a stream, harbor, etc. The part of a city or town on such land; wharf or dock area. [14]
2186	Watercourse	A stream of water, a river or a brook; also an artificial channel for the conveyance of water. [14]
2187	Wave Deltas	See washovers. [14]
2188	Wave: Short	A radio wave shorter than those of the standard broadcasting band. In oceanography, waves under conditions where the relative depth (water depth/wavelength) is greater than 0.5 and where the phase velocity is independent of water depth, but dependent upon wavelength. [14]
2189	Wave: Storm	A wind-generated sea surface wave of great height. See storm surge. [14]
2190	Wave: Tidal	The wave motion of the tides. In popular usage, any unusually high (and therefore destructive) water level along a shore. It usually refers to either a storm surge or tsunami. [14]
2191	International Commission For The Scientific Exploration Of The Mediterranean Sea (Icsem)	serves as liaison for research in Mediterranean laboratories; promotes international activities on behalf of countries bordering the Mediterranean. [14]
2192	LAT	Lowest astronomical tide (LAT); The lowest level astronomical tide that can be expected to occur under average meteorological conditions and under any combination of astronomical conditions. [24]
2193	HAT	Highest astronomical tide (HAT); The highest level astronomical tide that can be expected to occur under average meteorological conditions and under any combination of astronomical conditions. [24]
2194	Era	In geology, any of the main divisions of geological time. [14]
2195	Low	See depression. [14]
2196	Sea	The great body of salt water in general, as opposed to land; ocean. One of the smaller divisions of the oceans. The state of the surface of the ocean with regard to wave or swell, as a calm sea. See cross sea, head sea, beam sea, following sea, quartering sea, sugar loaf sea. [14]
2197	Surveying	Specifically, the science or art of making such measurements as are necessary to determine the relative position of points above, on, or beneath the surface of the earth, or to establish such points. Generally, the art of making a survey. [14]
2198	Aerial	See antenna. [14]
2199	Magnetic Field	The space in which a magnetic influence exists. [14]
2200	Satellite	A relatively small celestial body revolving around a planet. Name sometimes given to the fictitious bodies assumed in the harmonic analysis of tides. [14]
2201	Tidal Current	An alternating, horizontal movement of water associated with the rise and fall of the tide, these movements being caused by gravitational forces due to the relative motions of Moon, Sun, and Earth. [20]
2202	Sea Level	The height of the sea surface uninfluenced by wind waves and swell, which is frequently measured relative to a reference horizon. Observations of the sea level over a certain period are often evaluated to render minimum, maximum, and mean sea level. [14]
2203	Orientation	The act of establishing the correct relationship in direction with reference to the points of the compass. The state of being in correct relationship in direction with reference to the points of the compass. A map is in orientation when the map symbols are parallel with their corresponding ground features. A photograph is in orientation when it correctly presents the perspective view of the ground or when images on the photograph appear in the same direction from the point of observation as do the corresponding map symbols. See orientation of plane table, orientation of surveying instrument, orientation: photogrammetric. [14]
2204	Nodal Point	In optics, one of the two points on the optical axis of a lens (or a system of lenses) such that a ray emergent from the second point is parallel to the ray incident at the first. The first nodal point is referred to as the front nodal point or incident nodal point, and the second nodal point as the rear nodal point or emergent nodal point. An amphidromic point. In astronomy, a node. [14]
2205	Positioning	The process of determination of a position. [14]
2206	Oscillation	The variation, usually with time, of the magnitude of a quantity with respect to a specified reference when the magnitude is alternately greater and smaller than the reference. Half an oscillatory cycle, consisting of a fluctuation or vibration in one direction; half a vibration. [14]
2207	Spirit Level	See level. [14]
2208	Celestial Sphere	An imaginary sphere of infinite radius, concentric with the earth, on which celestial bodies are imagined to be projected. Also called celestial concave. [14]
2209	Magnetic Compass	See compass. [14]
2210	Oceanography	The study of the sea, embracing and integrating all knowledge pertaining to the sea's physical boundaries, the chemistry and physics of sea water, marine biology, and submarine geology. In strict usage oceanography is the description of the marine environment, whereas oceanology is the study of the oceans and related sciences. [14]
2211	Shallow Water	Commonly, water of such a depth that surface waves are noticeably affected by bottom topog-raphy. It is customary to consider water of depths less than half the surface wavelength as shallow water. [14]
2212	Water Bottle	A device for collecting water samples from varying depths. They are lowered in an 'open' state to the required depth and can be closed before being hauled up by means of a messenger. Water bottles can be operated in series that is with more than one bottle on the wire rope so that water samples can be taken at a number of depths on the same cast. Also called water specimen cup. [14]
2213	Nautical Chart	A chart specifically designed to meet the requirements of marine navigation, showing depths of water, nature of bottom, elevations, configuration and characteristics of coast, dangers and aids to navigation. May be a paper chart, electronic navigational chart (enc) or a raster navigational chart (rnc). Also called marine chart, hydrographic chart, or simply chart. - 2. (from solas chapter v) a special-purpose map or a specially compiled database from which a map is derived, that is issued officially by or on the authority of a government, authorized hydrographic office or other relevant government institution and is designed to meet the requirements of marine navigation. [14]
2214	Line Of Position	A line indicating a series of possible positions of a craft, determined by observation or measurement. Also called position line. See celestial line of position, circle of position, course line, electronic line of position, fix, hyperbolic line of position, latitude line, leading line, longitude line, retired line of position, sonic line of position, speed line, sumner line, surface of position, visual line of position. [14]
2215	Hydrographic Survey	See survey. [14]
2216	Transponder	A combined receiver and transmitter whose function is to transmit signals automatically when triggered by an interrogator. See transceiver. [14]
2217	Level: Spirit	A small closed vessel of glass (vial), having the inside surface of its upper part curved in form; the vessel is nearly filled with a fluid of low viscosity (alcohol or ether), enough free space being left for the formation of a bubble of air and gas, which will always assume a position at the top of the vessel. There are two types of spirit levels used in surveying: one has the curved surface spherical in form, producing a bubble of circular outline; and is properly called a circular level (also universal level or bull's eye level). The other and much more generally used type has a vessel in the form of circular tube, the longitudinal axis of which is also circular in form. It is the type usually referred to when the term 'spirit level' is used. The spirit level is also called spirit bubble or sensitive bubble. [14]
2218	Line Of Sight	The straight line between two points. This line is in the direction of a great circle, but does not follow the curvature of the earth. See also collimation: line of. [14]
2219	Nautical Mile	A unit of length used principally in navigation. See international nautical mile. [14]
2220	Displacement	In radiolocation, the half of the band of uncertainty having as its center line an electronic line of position. In photogrammetry, any shift in the position of an image on a photograph which does not alter the perspective characteristics of the photograph (i.e. Shift due to tilt of the photograph, scale change in the photograph, and relief of the objects photographed). [14]
2221	Echo Sounding	Determination of the depth of water by measuring the time interval between emission of a sonic or ultrasonic signal and return of its echo from the bottom. Also called acoustic sounding. See also echo sounder. [14]
2222	Dead Reckoning	A method of navigation utilizing only the speed and heading of the craft, without reference to external aids. In air navigation, the best estimate of course and speed over the ground is used, i.e., dead reckoning incorporates wind vector. [14]
2223	Vertical Plane	See plane. [14]
2224	Angular Distance	The angular difference between two directions, numerically equal to the angle between two lines extending in the given directions. The arc of the great circle joining two points, expressed in angular units. [14]
2225	Focal Length	The distance from the rear nodal point of a lens to the focal plane for an object at infinity. The distance from the surface of a mirror to its focus. Also called focal distance. [14]
2226	Control Point	A point on the ground whose position (horizontal and vertical) is used as a base for a dependent survey. Also referred to as control station.- 2. In photogrammetry, any point in a horizontal and vertical control system that is identified on a photograph and used for correlating the data shown on that photograph. More specific terms are photo-control point, picture control point and ground control point. [14]
2227	Current Meter	An instrument for the measurement of either speed alone or of both direction and speed of a current. See current pole, Ekman current meter, price-gurley current meter, roberts radio current meter, swallow float, savonius rotor current meter, wollaston current meter. [14]
2228	Establishment	The interval of time between the transit (upper or lower) of the moon and the next high water at a place. The average establishment at the time of full or new moon is called vulgar or common establishment, or high water full and change. Also called high water lunitidal interval, or establishment of the port. See lunitidal interval. [14]
2229	Sounding Line	A line of sounding. A lead line. [14]
2230	Celestial Pole	See pole. [14]
2231	Line Of Sounding	A series of soundings along a predetermined line, and at stated intervals, when surveying. Also referred to as sounding line. See check lines, cross lines, cross-section lines, inter line, split line, starred lines, track line of sounding, systems of sounding lines. [14]
2232	Tropical Cyclone	Cyclone of tropical origin of small diameter (some hundreds of kilometers). It is characterized by violent wind and torrential rain. Sometimes accompanied by a thunderstorm. [14]
2233	Water Sample	A portion of water brought up from a certain depth to determine its composition, or physical properties viz: temperature, salinity and density. [14]
2234	Magnetic Pole	Either of the two places on the surface of the earth where the magnetic dip is 90°, that in the northern hemisphere being designated north magnetic pole, and that in the southern hemisphere being designated south magnetic pole. The magnetic poles are not fixed and do not coincide with the geographical poles. Either of those two points of a magnet where the magnetic force is greatest. [14]
2235	Map Projection	See projection. [14]
2236	Mean Solar Day	See day: solar. [14]
2237	Principal Line	In photogrammetry, the trace of the principal plane upon the photograph, (e.g., the line through the principal point and the photograph nadir). [14]
2238	Vertical Circle	See circle. [14]
2239	Sextant Altitude	See under altitude. [14]
2240	Weather Forecast	Statement of the expected meteorological conditions for a specified period, and for specified area or portion of air space. [14]
2241	Relative Position	See position. [14]
2242	Perspective Centre	The point of origin or termination of bundles of perspective rays. The two such points usually associated with a survey photograph are the interior perspective center and the exterior perspective center. In a perfect lens-camera system, perspective rays from the interior perspective center to the photographic images enclose the same angles as the corresponding rays from the exterior perspective center to the objects photographed. In a lens having distortion this is true only for a particular zone of the photograph. In a perfectly adjusted lens-camera system the exterior and interior perspective centers correspond, respectively, to the front and rear nodal points of the camera lens. [14]
2243	Survey Sheet	See hydrographic survey sheet. [14]
2244	Levelling Rod	A straight rod or bar, designed for use in measuring a vertical distance between a point on the ground and the line of collimation of a levelling instrument which has been adjusted to horizontal position. Also called levelling staff. [14]
2245	Scale: Natural	The ratio between the linear dimensions of a chart, drawing, etc., and the actual linear dimensions represented, expressed as a proportion. Occasionally called representative fraction, fractional scale or numerical scale. [14]
2246	Horizontal Axis	See axis. [14]
2247	Principal Point	In photogrammetry, the foot of the perpendicular from the interior perspective center to the plane of the photograph (i.e. The foot of the photograph perpendicular). [14]
2248	Territorial Sea	A belt of water of a defined breadth but not exceeding 12 nautical miles measured seaward from the territorial sea baseline. [14]
2249	Zenith Distance	The vertical angle between the zenith and the object which is observed or defined. Zenith distance is the complement of the altitude. See zenith distance: double. [14]
2250	Meridian Transit	The apparent passage of a celestial body across a celestial meridian. Upper or superior transit is the passage across the upper branch of the celestial meridian. Lower or inferior transit is the passage across the lower branch. The lower transit may take place either above the horizon as is the case of circumpolar celestial bodies, or across that branch of the meridian lying below the observer's horizon. Also called transit, meridian passage, culmination. [14]
2251	Coordinate System	A fixed system of lines used to define the position of a point, line, or plane. [14]
2252	Pressure Gradient	Vector, perpendicular to the isobaric line or surface, directed towards low pressure and of intensity equal to the rate of variation of the pressure with distance. Also called barometric gradient. [14]
2253	Sextant: Sounding	(British terminology). A simplified and more robustly constructed version of the marine sextant intended primarily for use in hydrographic survey. It has no shades, a wide angle low magnification telescope and is generally graduated in minutes of arc. It may be fitted with either a vernier or a micrometer reading device. Both mirrors are silvered all over to enable angles up to 180° to be measured. Some sounding sextants have a 90° prism attachment which reflects the normal direct line of sight 90° to the left. Called surveying sextant, or hydrographic sextant in US Terminology. [14]
2254	Primary Great Circle	A great circle used as the origin of measurement of a coordinate; particularly such a circle 90° from the poles of a system of spherical coordinates, as the equator. Also called primary circle, fundamental circle. [14]
2255	Water Column	A vertical continuum of water from sea surface to sea-bed. [14]
2256	Depth Contour	See depth curve. [14]
2257	Ground Survey	See survey. [14]
2258	Level Surface	A surface which, at every point, is perpendicular to the direction of gravity. A level surface is an equipotential surface. The geoid or, in general, any surface parallel to it, is a level surface. If changes in elevation due to tides, winds, etc. Are neglected, the surface of the sea is a level surface. A level surface is not a plane surface, but it is sometimes so regarded in surveys of limited areas. [14]
2259	Range Of Tide	The difference in height between consecutive high and low tides at a place. Also called tidal (or tide) range. [14]
2260	Coriolis Force	Composite centrifugal force, due to the rotation of the earth, which acts on moving particles, whose motion is considered relative to that of the earth. [14]
2261	Height Of Tide	The vertical distance from the chart datum to the level of the water at any time. [14]
2262	Mercator Chart	See chart. [14]
2263	Objective Lens	In telescopes and microscopes, the optical component which receives light from the object and forms the first or primary image. In a camera, the image formed by the objective lens is the final image. In a telescope or microscope used visually, the image formed by the objective lens is magnified by the eyepiece. Also called objective or object-glass. [14]
2264	Reconnaissance	In surveying, a general examination or survey of the main features, or certain specific features, of a region, usually as a preliminary to a more detailed survey. An examination of an area to gain specific information, as the weather conditions, extent and nature of ice, etc. [14]
2265	Sounding Datum	See datum. [14]
2266	Magnetic Needle	A small, slender magnetized bar which tends to align itself with magnetic lines of force. [14]
2267	Navigation Mark	An artificial or natural object of easily recognizable shape or colour, or both, situated in such a position that it may be identified on a chart or related to a known navigational instruction. Alternative term for visual aid to navigation. Includes both buoys and beacons (fixed artificial navigation mark). [14]
2268	Collimation Axis	The line through the optical center of the objective lens perpendicular to the axis of rotation of the telescope. Also called axis of collimation. [14]
2269	Error Of Closure	The amount by which a quantity obtained by a series of related measurements differs from the true or fixed value of the same quantity. Also called closing error. [14]
2270	Geodetic Equator	See equator. [14]
2271	Horizontal Plane	See plane. [14]
2272	Vertical Control	See control. [14]
2273	Eccentric Station	A survey point over which an instrument is centered and observations are made, which is not in the same vertical line with the station it represents, and to which the observations will be reduced before being combined with observations at other stations. Also called false station or satellite station. See eccentric reduction. [14]
2274	Greenhouse Effect	The warming of an atmosphere by its absorbing and emitting infrared radiation while allowing shortwave radiation to pass on through. The gases mainly responsible for the earth's atmospheric greenhouse effect are water vapor and carbon dioxide. See atmospheric greenhouse effect. [1]
2275	Celestial Meridian	See meridian. [14]
2276	Current: Reversing	A tidal current which flows alternately in approximately opposite directions, with slack water at each reversal. Such currents occur principally in areas where motion is largely restricted to relatively narrow channels. Also called rectilinear current or rectilinear stream. [14]
2277	Oblique Photograph	See photograph. [14]
2278	Harmonic Constituent	One of the harmonic elements in a mathematical expression for the tide-producing force, and in corresponding formulae for the tide or tidal current. Each constituent represents a periodic change or variation in the relative positions of the earth, sun and moon. Also called tidal constituent or component. [14]
2279	True Horizon	See horizon. [14]
2280	Acoustic Wave	See wave: sound. [14]
2281	Apparent Time	See time: apparent solar. [14]
2282	Earth'S Crust	See crust. [14]
2283	Fixed Station	A radiolocation station which is situated in one particular spot throughout the period of its operation. As opposed to mobile station. Also called shore station.in oceanography, a platform from which repeated observations are taken. These include coastal and island stations, light vessels, weather ships, automatic floating stations and ice islands. Also called fixed platform. [14]
2284	Geodesic Line	The shortest line on a mathematically derived surface, between two points on that surface. A geodesic line on a reference spheroid is called a geodetic line. Also termed a geodesic. [14]
2285	Least Squares	A method of adjusting observations in which the sum of the squares of all the deviations or residuals derived in fitting the observations to a mathematical model, is made a minimum. Least squares have also been designated as minimum squares. [14]
2286	Nansen Bottle	A device used by oceanographers to obtain subsurface samples of sea water. The bottle is lowered by wire; its valves are open at both ends. It is then closed 'in situ' by allowing a weight (called a messenger) to slide down the wire and strike the reversing mechanism. This causes the bottle to turn upside down, closing the valves and reversing the reversing thermometers which are mounted in a special thermometer case on it. If, as is usually done, a series of bottles is lowered, then the reversal of each bottle releases another messenger to actuate the bottle beneath it. [14]
2287	Nodical Month	See month. [14]
2288	Ocean Current	See current. [14]
2289	Radial Centre	In photogrammetry, the selected point on a photograph from which radials (directions) to various image points are drawn or measured (i.e., the origin of radials). The radial center is either the principal point, the nadir point, the isocenter, or a substitute center. [14]
2290	Radio Station	A place equipped to transmit radio waves. Such a station may be either stationary or mobile, and may also be provided with a radio receiver. In British terminology, also called w/t station. [14]
2291	Radius Vector	A straight line connecting a fixed reference point or center with a second point, which may be moving. In astronomy, the expression is usually used to refer to the straight line connecting a cele-stial body with another which revolves around it, as a radius vector of the earth and moon. See coordinates: plane polar and coordinates: polar. [14]
2292	Stand Of Tide	The condition at high tide or low tide when there is no change in the height of the water. It may be called high water stand if it occurs at the time of high tide, and low water stand if it occurs at low tide. Also called stand. [14]
2293	Station: Tide	A place where tidal observations are obtained. It is a primary tide station when continuous observations are available for a sufficient number of years to determine the characteristic tide features for the locality. A secondary tide station is operated during a short period of time to obtain data for a specific purpose. [14]
2294	Swinging Ship	The process of placing a vessel on various headings and comparing magnetic compass readings with the corresponding magnetic directions, to determine deviation. This usually follows compass compensation (or adjustment), and is done to obtain information for making a deviation table. Also called compass calibration, or calibration of compass. See compensation of magnetic compass. [14]
2295	Air Navigation	See navigation. [14]
2296	Diurnal Motion	The apparent daily motion of a celestial body. [14]
2297	Frequency Band	See band of frequency. [14]
2298	Geodetic Datum	See datum. [14]
2299	Gradient Tints	See hypsometric tints. [14]
2300	Ground Control	See control. [14]
2301	On The Quarter	Bearing approximately 135° relative (on the starboard quarter) or 225° relative (on the port quarter). The expression is often used loosely for broad on the quarter, or bearing exactly 135° or 225° relative. See also broad on the quarter. [14]
2302	Personal Error	See error. [14]
2303	Prime Vertical	See prime vertical circle. [14]
2304	Time: Apparent	See time: apparent solar. [14]
2305	Wind Direction	The direction from which the wind is blowing. [1]
2306	Control Station	see control point . [14]
2307	Lens Distortion	See distortion. [14]
2308	Modulating Wave	See wave. [14]
2309	Parhelic Circle	Photometeor of the halo family, consisting of a white, horizontal circle, situated at the same angular height as the sun. [14]
2310	Plane Surveying	See surveying. [14]
2311	Principal Plane	In photogrammetry, the vertical plane through the internal perspective center containing the photograph perpendicular of a tilted photograph. [14]
2312	Relative Motion	Motion of one object or body relative to another. The expression is usually used in connection with problems involving motion of one craft, torpedo, or missile relative to another, the direction of such motion being called direction of relative movement, and the speed of such motion being called speed of relative movement or relative speed. Usually called apparent motion when applied to the change of position of a celestial body as observed from the earth. Also called relative movement. [14]
2313	Station Pointer	(British terminology). A metal instrument with three legs, a circle graduated in degrees and 1/2 degrees, and a vernier or micrometer for setting the angles. See also protractor: three arm. [14]
2314	Axis Of Homology	In photogrammetry, the intersection of the plane of the photograph with the horizontal plane of the map or the plane of reference of the ground. Corresponding lines in the photograph and map planes intersect on the axis of homology. Also called the axis of perspective, or map parallel. [14]
2315	Central Meridian	See meridian: initial. [14]
2316	Compass: Hanging	A compass having its binnacle overhead and its graduated card facing downward. Also referred to as overhead compass, or inverted compass. [14]
2317	Direction Finder	See radio direction finder. [14]
2318	Mean Water Level	The average surface level of a body of water. [14]
2319	Oscillatory Wave	See wave. [14]
2320	Parallax: Annual	The angle subtended at a celestial body by the radius of earth's orbit. Also called heliocentric parallax, or stellar parallax. [14]
2321	Aid To Navigation	A visual, acoustical, or radio device, external to a ship, designed to assist in determining a safe course or a vessel ™s position, or to warn of dangers and/or obstructions. Aids to navigation usually include buoys, beacons, fog signals, lights, radio beacons, leading marks, radio position fixing systems and gnss which are chart-related and assist safe navigation. [14]
2322	Bottom: Nature Of	The feature of the bottom including the material of which it is composed and its physical characteristics. Also called character (or characteristics) of the bottom, or quality of the bottom. [14]
2323	Geodetic Meridian	See meridian. [14]
2324	Horizontal Circle	See circle. [14]
2325	Parallactic Angle	That angle of the astronomical triangle at the celestial body; the angle between a body's hour circle and its vertical circle. Also called position angle.in photogrammetry, the angle subtended by the eye of the observer at the object viewed. Also called angle of convergence or angular parallax. [14]
2326	Personal Equation	The time interval between the sensory perception of a phenomenon and the motor reaction thereto. Personal equation may be either positive or negative, as an observer may anticipate the occurrence of an event, or wait until he actually sees it occur before making a record. This is a syste-matic error, treated as of the constant type. It is a personal error, for which the term personal equation is reserved. It is of special significance in observations of time, made to determine chronometer correction. [14]
2327	Reference Station	See station. [14]
2328	Stereoscopic Pair	In photogrammetry, two photographs of the same area taken from different air stations so as to afford stereoscopic vision. Frequently called a stereopair. [14]
2329	Altitude: Apparent	The sextant altitude of a celestial body corrected for index error, dip (height of eye), and (for sun or moon only) semidiameter. Also called rectified altitude. [14]
2330	Angle Of Incidence	The angle between the line of motion of a ray and the perpendicular to a surface at the point of impingement. [14]
2331	Geodetic Longitude	See longitude. [14]
2332	Greenwich Meridian	See meridian. [14]
2333	Low Water Interval	See lunitidal interval. [14]
2334	Phototriangulation	The process for the extension of horizontal and/or vertical control whereby the measurements of angles and/or distances on overlapping photographs are related into a spatial solution using the perspective principles of the photographs. Generally, this process involves using aerial photographs, and is called aero triangulation, aerial triangulation, or photogrammetric extension. [14]
2335	Temporal Variation	See magnetic temporal variation. [14]
2336	Aberration Of Light	Astronomy, the apparent displacement in position of a heavenly body caused by the combination of the velocity of light and that of an observer on the surface of the earth. Aberration of light due to the rotation of the earth on its axis is termeddiurnal aberration. That due to the revolution of the earth around the sun is termedannual aberration. In optics, failure of an optical system to bring all light rays received from a point object to a single image point or to a prescribed geometric position. Spherical aberration is caused by rays from various zones of a lens or mirror coming to focus at different distances from the lens or mirror. Chromatic aberration(orchromatism) is due to the differences in refraction of the coloured rays of the spectrum; those of each colour having a different focus. [14]
2337	Closure Of Triangle	See error of closure of triangle. [14]
2338	Radial Triangulation	The aero triangulation procedure, either graphical or analytical, in which directions from the radial center, or approximate radial center, of each overlapping photograph are used for horizontal-control extension by the successive intersection and resection of these direction lines. A radial triangulation also is correctly called a radial plot or a minor-control plot. If made by analytical methods, it is called an analytical radial triangulation. A radial triangulation is assumed to be graphical unless prefixed by the word analytical. [14]
2339	Tape: Sag Correction	The difference between the effective length of a tape (or part of a tape) when supported continuously throughout its length and when supported at a limited number of independent points. Also called catenary correction. [14]
2340	Electronic Navigation	See navigation. [14]
2341	Spheroid Of Reference	See reference spheroid. [14]
2342	Flattening Of The Earth	The ratio of the difference between the equatorial and polar radii of the earth (major and minor semi-axes of the spheroid) and its equatorial radius (major semi-axis). The flattening of the earth is the ellipticity of the spheroid. Also called compression. [14]
2343	Weather Ship	See ocean station vessel. [14]
2344	Aerial Camera	See camera. [14]
2345	Aerial Survey	See survey. [14]
2346	Annual Change	See magnetic annual change. [14]
2347	Azimuth Angle	Azimuth measured from 0° at the north or south reference direction clockwise or counter-clockwise through 90° or 180°. It is labelled with the reference direction as a prefix and the direction of measurement from the reference direction as a suffix. [14]
2348	Azimuth: Back	An azimuth 180° from a given azimuth. In geodesy, the direction of the line ba as distinguished from the forward azimuth ab. The two differ by 180° plus the amount of convergence of the meridians between points a and b. Also called reverse azimuth. See azimuth: geodetic. [14]
2349	Bottom Sample	A portion of the sea bottom material brought to the surface for examination. See also core. [14]
2350	Drift Current	See current. [14]
2351	Floating Mark	In photogrammetry, a mark seen as occupying a position in the three-dimensional space formed by the stereoscopic fusion of a pair of photographs and used as a reference mark in examining or measuring the stereoscopic model. [14]
2352	Heavenly Body	See celestial body. [14]
2353	Horizon Glass	That glass of a marine sextant, attached to the frame, through which the horizon is observed. That half of this glass nearer the frame is silvered to form the horizon mirror for reflecting the image of a celestial body; the other half is clear. [14]
2354	Initial Point	The origin of a system in the rectangular system of surveys of which a principal meridian and a base line constitute the axes for a given area. Also called fundamental point. [14]
2355	Inner Harbour	See under harbor. [14]
2356	Leading Marks	(British terminology). Aids to navigation or other indicators so located as to indicate the path to be followed. Leading marks identify a leading line when they are in transit. See also range. [14]
2357	Luminous Flux	See flux. [14]
2358	Magnetization	The degree to which a body is magnetized. The magnetic moment per unit volume. Also called intensity of magnetization. [14]
2359	Plane Sailing	See sailing. [14]
2360	Position Line	See line of position. [14]
2361	Radiolocation	Determination of position or of a line of position by means of radio equipment. See navigation: electronic. [14]
2362	Rectification	The process of projecting a tilted or oblique photograph onto an horizontal reference plane, the angular relationship between the photograph and the plane being determined by ground methods. [14]
2363	Regular Error	See error: systematic. [14]
2364	Sidereal Time	See time. [14]
2365	Standing Wave	See wave. [14]
2366	Survey Signal	See signal. [14]
2367	Tide: Diurnal	A tide in which the tidal cycle consists of one high water and one low water each tidal day. In British terminology also called single day tide. [14]
2368	Tilting Level	See levelling instrument: tilting level. [14]
2369	Tropical Year	See year. [14]
2370	True Altitude	See altitude. [14]
2371	Turning Point	In levelling, a point on which both a minus sight (foresight) and a plus sight (backsight) are taken on a line of direct levelling. In topographic surveys, any point on which the rod is held while the instrument (plane table) is moved to another station. In a traverse, any point of junction of two legs. Also called traverse point. [14]
2372	Valley Breeze	A local wind system of a mountain valley that blows downhill (mountain breeze) at night and uphill (valley breeze) during the day. See mountain breeze. [1]
2373	Wave Spectrum	In ocean wave studies, a graph showing the distribution of wave heights with respect to frequency in a wave record. [14]
2374	Wind Spectrum	Measure of the variance associated with the fluctuating wind speed per unit frequency band. NOTE 1 The wind spectrum is an expression of the dynamic properties of the wind (turbulence). It reflects the fluctuations about and in the same direction as a certain mean wind speed, usually the 1 h sustained wind speed. There is hence no direction variable associated with the wind spectrum within this document. NOTE 2 As the sustained wind speed varies with elevation, the wind spectrum is a function of elevation. [15]
2375	Bearing: Sonic	A bearing determined by measuring the direction from which a sound wave is coming. Also called acoustic bearing. [14]
2376	Climate Change	A change in the long-term statistical average of weather elements such as temperature or precipitation sustained over several decades or longer. Climate change is also called climatic change. [1]
2377	Current Tables	Tables listing predictions of the times and speeds of tidal currents at various places, and other pertinent information. Also called tidal current tables. [14]
2378	Land Territory	Continental or insular land masses that are above water at high tide. [14]
2379	Low Water Line	See low water mark. [14]
2380	Magnetic North	See north. [14]
2381	Optical Centre	The point of intersection of lines which represent within the lens those rays whose emergent directions are parallel to their respective incident directions. This point lies on the optical axis. [14]
2382	Optical System	A series of lenses, apertures, prisms, mirrors, etc., so arranged as to perform a definite optical function. [14]
2383	Phantom Bottom	A false bottom indicated by an echo sounder, some distance above the actual bottom. Such an indication, quite common in the deeper parts of the ocean, is due to large quantities of small organisms. Also called deep scattering layer (DSL) or false bottom. [14]
2384	Plotting Sheet	A blank chart, usually on the Mercator projection, showing only the graticule and a compass rose, so that the plotting sheet can be used for any longitude. In hydrographic surveying, a working sheet on which the main stations of the survey are plotted. It forms the framework of the survey and provides the basis for accurately locating and plotting all the detail of the survey. See also lattice. [14]
2385	Radar: Primary	Radar which transmits a signal and receives the incident energy reflected from an object to detect the object in contrast to secondary radar which receives pulses from a transponder triggered by pulses transmitted from the radar. [14]
2386	Reference Line	Any line which can serve as a reference or base for the measurement of other quantities. Also called datum line. [14]
2387	Secular Change	An increase or decrease of intensity and/or change of direction of the total magnetic field over a period of many years. [14]
2388	Sound Pressure	See pressure. [14]
2389	Sound Velocity	The rate of motion at which sound energy moves through a medium. The velocity of sound in sea water is a function of temperature, salinity, and the changes in pressure associated with changes in depth. An increase in any of these factors tends to increase the velocity. [14]
2390	Tropical Storm	Organized thunderstorms with a cyclonic wind circulation between 35 and 64 knots. [1]
2391	Vernal Equinox	The equinox at which the sun approaches the northern hemisphere and passes directly over the equator. Occurs around march 20. [1]
2392	Year: Tropical	The period of one revolution of the earth around the sun, with respect to the vernal equinox. Because of precession of the equinoxes, this is not 360° with respect to the stars, but 50".3 less. A tropical year is about 20 minutes shorter than a sidereal year, averaging 365 days, 5 hours, 48 minutes, and 46 seconds in 1900 and is decreasing at the rate of 0.00530 second annually. Also called astronomical, equinoctial, natural, or solar year. [14]
2393	Bouguer Anomaly	A difference between an observed value of gravity and a theoretical value at the point of observation, which has been corrected for the effect of the topography and elevation only, the topography being considered as resting on a plane of indefinite extent. [14]
2394	Cardinal Points	The four points of the horizon at the intersections of the horizon with the meridian and the prime vertical; the north, south, east and west points. [14]
2395	Chart: Gnomonic	A chart on the gnomonic projection. Also called great circle chart. [14]
2396	Chart: Nautical	A chart specifically designed to meet the requirements of marine navigation, showing depths of water, nature of bottom, elevations, configuration and characteristics of coast, dangers and aids to navigation. Also called marine chart, hydrographic chart, or simply chart. [14]
2397	Compass: Liquid	A magnetic compass having a bowl completely filled with liquid in order to damp the swinging of the card. Sometimes called spirit compass, or wet compass. [14]
2398	Coordinate Axes	See coordinates: plane rectangular. [14]
2399	Current Station	The geographic location at which current observations are conducted. Also, the facilities used to make current observations. These may include a buoy, ground tackle, current meters, recording mechanism, and radio transmitter. See control current station and subordinate current station. [14]
2400	Data Processing	Any operation carried out with data usually with the help of a computer. [14]
2401	Error: Standard	The square root of the arithmetic mean of squared deviations from the mean. Also called standard deviation, when the deviations do not represent errors, or root mean square error. [14]
2402	Flight Altitude	See altitude. [14]
2403	Gust Wind Speed	Maximum value of the wind speed of a gust averaged over a short (3 s to 60 s) specified duration within a longer (1 min to 1 h) specified duration. NOTE 1 For design purposes, the specified duration depends on the dimensions and natural period of the (part of the) structure being designed such that the structure is designed for the most onerous conditions; thus, a small part of a structure is designed for a shorter gust wind speed duration (and hence a higher gust wind speed) than a larger (part of a) structure. NOTE 2 In practice, for design purposes, the gust wind speeds for different durations (e.g. 3 s, 5 s, 15 s, 60 s) are derived from the wind spectrum. [15]
2404	High Water Line	See high water mark. [14]
2405	Mean Solar Time	See time. [14]
2406	Navigation: Air	The navigation of aircraft. Occasionally called aerial navigation or navigation. See navigation: surface. [14]
2407	Oblate Spheroid	See spheroid. [14]
2408	Orthophotograph	A photographic copy, prepared from a perspective photograph, in which the displacements of images due to tilt and relief have been removed. [14]
2409	Point Of Origin	See coordinates: origin of. [14]
2410	Pole: Celestial	Either of the two points of intersection of the celestial sphere and the extended axis of the earth, labelled n or s to indicate either the north celestial pole or the south celestial pole. [14]
2411	Reference Level	See datum: chart and datum: vertical control. [14]
2412	Repetition Rate	The rate at which recurrent signals are transmitted. Also called recurrence rate. [14]
2413	Scatter Diagram	Joint probability of two or more (metocean) parameters. NOTE A scatter diagram is especially used with wave parameters in the metocean context. The wave scatter diagram is commonly understood to be the probability of the joint occurrence of the significant wave height (Hs) and a representative period (Tz or Tp). [15]
2414	Side Scan Sonar	A form of active sonar in which fixed acoustic beams are directed into the water perpendicularly to the direction of travel to scan the bottom and generate a record of the bottom configuration. [14]
2415	Synodical Month	See month. [14]
2416	Time: Greenwich	Time based upon the Greenwich meridian as reference. [14]
2417	Topographic Map	See map. [14]
2418	Transit Passage	In straits used for international navigation, all ships and aircraft enjoy the unimpeded right of transit passage. This means the freedom of navigation and overflight solely for the purpose of continuous and expeditious transit of the strait between one part of the high seas or an exclusive economic zone and another part of the high seas or an exclusive economic zone. See also innocent passage. [14]
2419	Vectorial Angle	See coordinates: plane polar. [14]
2420	Wire Drag Sweep	See survey: wire drag. [14]
2421	Altimeter: Radio	Any instrument used for determining an aircraft's flight altitude by the measurement of time intervals between the emission and return of electromagnetic pulses. Also called pulse radio altimeter or radar altimeter. See altitude: flight. [14]
2422	Annual Variation	See magnetic annual variation. [14]
2423	Apparent Horizon	See horizon. [14]
2424	Differential Gps	Differential gps is implemented by placing a gps monitor receiver at a precisely known location. Instead of computing a navigation fix, the monitor determines the range error to every gps satellite it can track. These ranging errors are then transmitted to local users where they are applied as corrections before computing the navigation result. [14]
2425	Eccentric Signal	A signal which is not in the same vertical line with the station it represents. [14]
2426	Equilibrium Tide	See tide. [14]
2427	Greenhouse Gases	Gases in the earth's atmosphere, such as water vapor and carbon dioxide, that allow much of the sunlight to pass through but are strong absorbers of infrared energy emitted by the earth and the atmosphere. Other greenhouse gases include methane, nitrous oxide, fluorocarbons, and ozone. [1]
2428	Magnetic Element	Variation, dip, or magnetic intensity. [14]
2429	Micrometer Screw	A finely threaded screw of definite pitch, with a head graduated to show how much the screw has been moved in or out; used in micrometers. [14]
2430	Radio Navigation	See navigation: electronic. [14]
2431	Rear Nodal Point	See nodal point. [14]
2432	Semidiurnal Tide	See tide. [14]
2433	Spring Low Water	See mean low water springs. [14]
2434	Systematic Error	See error. [14]
2435	Weather Analysis	Operation of studying the general state of the atmosphere over a region, with respect to synoptic charts. Also called synoptic analysis. [14]
2436	Aerotriangulation	See phototriangulation. [14]
2437	Bathymetric Chart	See chart. [14]
2438	Celestial Horizon	See horizon. [14]
2439	Centre Of Gravity	See gravity. [14]
2440	Geodetic Latitude	See latitude. [14]
2441	Geomagnetic Field	The magnetic field of the earth. Also called terrestrial magnetic field or earth's magnetic field. [14]
2442	Marine Navigation	See navigation. [14]
2443	Navigation: Sonic	Avigation by means of sound waves whether or not they are within the audible range. Also called acoustic navigation. [14]
2444	Parallax: Diurnal	The difference in the apparent direction or position of a celestial body as observed from the center of the earth and a point on its surface. This varies with the body's altitude and distance from the earth. Also called geocentric parallax. [14]
2445	Stability: Static	State of hydrostatic equilibrium of the atmosphere in which a particle of air moved from its initial level undergoes a hydrostatic force which tends to restore it to this level. Also called hydrostatic stability. [14]
2446	Strip Coordinates	See coordinates. [14]
2447	Telecommunication	Any transmission, emission, or reception of signs, signals, writing, images and sounds or intelligence of any nature by wire, radio, visual or other electromagnetic systems. [14]
2448	Triangulation Net	Arcs of triangulation, sometimes with lines of traverse, connected together to form a system of loops or circuits extending over an area. Sometimes called tie net when used to tie small islands together. Also called traverse net or survey net. [14]
2449	Aerial Photography	See photography. [14]
2450	Circle Of Latitude	A great circle of the celestial sphere through the ecliptic poles, and hence perpendicular to the plane of the ecliptic. [14]
2451	Condition Equation	See equation. [14]
2452	Continental Margin	The zone, generally consisting of shelf, slope and continental rise, separating the continent from the abyssal plain or deep sea floor. [14]
2453	Dry Adiabatic Rate	The rate of change of temperature in a rising or descending unsaturated air parcel. The rate of adiabatic cooling or warming is about 10°c per 1000 m (5.5°f per 1000 ft). [1]
2454	Hayford'S Spheroid	The spheroid based upon an investigation made in 1909 by hayford, a geodesist of US Coast & geodetic survey, using the large triangulation net then existing in the US A., and taking into account the inequal density of the earth's crust. The geodetic and geophysical union (now the international union of geodesy and geophysics) adopted in 1924 the hayford's spheroid (with some slight modifications) as the international ellipsoid of reference. [14]
2455	Infrared Radiation	Electromagnetic radiation with wavelengths between about 0.7 and 1000 mm. This radiation is longer than visible radiation but shorter than microwave radiation. [1]
2456	Luminous Intensity	See intensity. [14]
2457	Photochemical Smog	Originally smog meant a mixture of smoke and fog. Today, smog means air that has restricted visibility due to pollution, or pollution formed in the presence of sunlight, photochemical smog. Also see smog. [1]
2458	Thermometric Depth	See depth. [14]
2459	Topographic Survey	See survey. [14]
2460	Angle Of Refraction	The angle between a refracted ray and the perpendicular to the refraction surface. [14]
2461	Figure Of The Earth	The defining elements of the mathematical surface which approximates the surface of the geoid. The figure of the earth has been proved to be approximately an oblate spheroid. See also geoid and spheroid. [14]
2462	Geocentric Parallax	See parallax: diurnal. [14]
2463	Horizontal Parallax	See parallax. [14]
2464	Line Of Collimation	See collimation. [14]
2465	Mercator Projection	See projection. [14]
2466	Micrometer: Transit	A form of registering micrometer with its movable wire placed in the focal plane of an astronomic transit and at right angles to the direction of motion of the image of a star which is observed at or near culmination. The transit micrometer is also termed an impersonal micrometer, because it almost completely eliminates the effect of the personal equation on time observations made with it. [14]
2467	Reference Direction	A direction used as a basis for comparison of other directions. [14]
2468	Topographic Feature	A single feature of the surface of the earth such as a mountain or valley. [14]
2469	Coastwise Navigation	See navigation. [14]
2470	Course: Great Circle	The direction of the great circle through the point of departure and the destination, expressed as the angular distance from a reference direction, usually north, to the direction of the great circle. The angle varies from point to point along the great circle. At the point of departure it is called initial great-circle course; at the destination it is called final great-circle course. [14]
2471	Density Of Soundings	Intervals between lines of sounding and soundings in the same line. Density of soundings mostly depends on the scale and nature of the survey. Also called frequency of soundings. [14]
2472	Hydrostatic Pressure	See pressure. [14]
2473	Interior Orientation	See orientation. [14]
2474	Levelling Instrument	An instrument designed for the accurate measurement of height differences by the process of levelling. Its essential parts are a telescope and a spirit level. Also called a level. [14]
2475	Magnetism: Permanent	Magnetism which is retained for long periods without appreciable reduction, unless the magnet is subjected to a demagnetizing force. Because of the slow dissipation of such magnetism, it is sometimes called subpermanent magnetism. [14]
2476	Moist Adiabatic Rate	The rate of change of temperature in a rising or descending saturated air parcel. The rate of cooling or warming varies but a common value of 6°c per 1000 m (3.3°f per 1000 ft) is used. [1]
2477	Multiple Lens Camera	See camera. [14]
2478	Nature Of The Bottom	See bottom: nature of. [14]
2479	Navigational Warning	A message containing urgent information relevant to safe navigation broadcast to ships in accordance with the provisions of the international convention for the safety of life at sea, 1974, as amended. See coastal warning, local warning, navarea warning. [14]
2480	Oceanographic Survey	See survey. [14]
2481	Micrometer Microscope	A filar micrometer so placed that its wire moves in the focal plane of a microscope. [14]
2482	Projection: Conformal	A projection in which all angles around any point are correctly represented. In such a projection the scale is the same in all directions about any point. Very small shapes are correctly represented, resulting in an orthomorphic projection. Hence, the terms of 'conformal' and 'orthomorphic' are used synonymously since neither characteristic can exist independently of the other. [14]
2483	Reversing Thermometer	See thermometer. [14]
2484	Triangulation Station	See station. [14]
2485	Radio Direction Finder	Radio receiving equipment which determines the direction of arrival of a signal by measuring the orientation of the wave front or of the magnetic or electric vector. Radio direction finders may be either manual or automatic. Also called direction finder. Formerly called radio compass. [14]
2486	Reduction Of Soundings	The correction of the observed depths, for the height of tide above or below the plane of reference at the time of sounding. Usually the term reduction of soundings does not cover corrections other than those due to tide. See correction of soundings, lead line correction and tide reducer. [14]
2487	Tape: Grade Correction	A correction applied to a distance measured on a slope to reduce it to a horizontal distance between the vertical lines through its end points. Also termed slope correction or correction for inclination of tape. [14]
2488	Chart (Or Map): Weather	Geographical map on which meteorological conditions or elements are represented by figures, symbols, or isopleths. Also called synoptic chart (or map). [14]
2489	Orthomorphic Projection	See projection: conformal. [14]
2490	Mean Zero-Crossing Period	Average period of the (up or down) zero-crossing waves in a sea state. NOTE In practice the mean zero-crossing period is often estimated from the zeroth and second moments of the wave spectrum as T_z= T_2= √(m_0 (f)/m_2 (f) )=2π√(m_0 (ω)/m_2 (ω) ) [15]
2491	Weather Tide	See tide: windward. [14]
2492	Abyssal Plain	An extensive, flat, gently sloping or nearly level region at abyssal depths. [14]
2493	Accommodation	The faculty of the human eye to adjust itself to give sharp images for different object distances. In stereoscopy, the ability of the eyes to bring two images into superimposition for stereoscopic viewing. [14]
2494	Aperture Stop	The physical element (such as a diaphragm, or lens periphery) of an optical system which limits the size of the pencil of rays traversing the system. Also called thestop. Diameter of that part of the lens actually used. [14]
2495	Apparent Noon	See noon. [14]
2496	Apparent Wind	See relative wind. [14]
2497	Azimuth: Grid	The angle in the plane of projection between a straight line and the y-axis of a plane-rectangular coordinate system. See bearing: grid. [14]
2498	Blind Rollers	Long, high swells which have increased in height, almost to the breaking point, as they pass over shoals or run in shoaling water. Called blind seas in some localities. [14]
2499	Boundary Wave	See wave: internal. [14]
2500	Cadastral Map	See map. [14]
2501	Closing Error	See error of closure. [14]
2502	Codeclination	90° minus the declination. See polar distance. [14]
2503	Compound Tide	See tide. [14]
2504	Contact Glass	See focal plane plate. [14]
2505	Contact Plate	See focal plane plate. [14]
2506	Contact Print	See print. [14]
2507	Current Cycle	A complete set of tidal current conditions, as those occurring during a tidal day, lunar month, or metonic cycle. [14]
2508	Diurnal Range	See range. [14]
2509	Doppler Radar	A radar that determines the velocity of falling precipitation either toward or away from the radar unit by taking into account the doppler shift. [1]
2510	Draft Forward	See draft. [14]
2511	Earth Current	See current(s): telluric. [14]
2512	Elevated Pole	See pole. [14]
2513	Exercise Area	An area shown on charts within which naval, military or aerial exercises are carried out. Also called military practice area. [14]
2514	False Station	See eccentric station. [14]
2515	Farewell Buoy	The outermost buoy marking the entrance to a channel or harbor. Also called sea buoy. Known as landfall buoy in British terminology. [14]
2516	Fiducial Axes	In photogrammetry, the lines joining opposite fiducial marks on a photograph. Also called photograph axes. [14]
2517	First Quarter	See phases of the moon. [14]
2518	Flood Current	See flood stream. [14]
2519	Geodetic Line	See geodesic line. [14]
2520	Grid Meridian	See meridian. [14]
2521	Gyro Repeater	An electrically operated dial repeating at a distance the indications of the master gyro compass. [14]
2522	Harbour Works	Permanent man-made structures built along the coast which form an integral part of the harbor system such as jetties, moles, quays or other port facilities, coastal terminals, wharves, breakwaters, sea walls, etc. [14]
2523	Heeling Error	See error. [14]
2524	Horizon Trace	In photogrammetry, an imaginary line, in the plane of a photograph, which represents the image of the true horizon; it corresponds to the intersection of the plane of a photograph and the horizontal plane containing the internal perspective center or rear nodal point of the lens. Also called horizon line. [14]
2525	Hummocked Ice	Sea ice piled haphazardly one piece over another, and which may be weathered. [14]
2526	Internal Wave	See wave. [14]
2527	Interpolation	The process of determining intermediate values between given values in accordance with some known or assumed rate or system of variation. [14]
2528	Isobathytherm	A line or surface showing the depths in oceans or lakes at which points have the same temperature. Isobathytherms are usually drawn to show cross sections of the water mass. [14]
2529	Isogonic Line	A line connecting points of equal magnetic variation. Also called isogonal (or isogonic). [14]
2530	Junction Buoy	A buoy marking the inner end of a middle ground. Usually called a middle ground buoy in British terminology, without regard to direction of travel. [14]
2531	Latitude Line	A line of position extending in a generally east-west direction. [14]
2532	Local Warning	a navigational warning which covers inshore waters, often within the limits of jurisdiction of a harbor or port authority. [14]
2533	Lookout Tower	Any tower surmounted by a small house in which a watch is habitually kept, as distinguished from an observation tower in which no watch is kept. [14]
2534	Lost' Station	see station: unrecoverable. [14]
2535	Lower Transit	See meridian transit. [14]
2536	Lunar Eclipse	See eclipse. [14]
2537	Magnification	The apparent enlargement of anything. In optics, the term relates to the properties of lenses and lens systems to produce an image which differs in dimension from the related object. [14]
2538	Marker Beacon	A radio beacon which radiates a signal to define an area, as an aid to navigation. Usually called marker radio beacon or marker. [14]
2539	Median Valley	The axial depression of the mid-oceanic ridge system. See rift. [14]
2540	Metonic Cycle	A period of 19 years, after which the various phases of the moon fall on approximately the same days of the year as in the previous cycle. [14]
2541	Metric System	A system of weights and measures, based upon the metre. [14]
2542	Minor Control	See control: photogrammetric. [14]
2543	Mother Vessel	The lead vessel when surveying with several vessels. [14]
2544	Nocturnal Arc	See arc: astronomical. [14]
2545	Observed Tide	Those data from tide observing equipment such as tide gauges, staffs, etc. "actual tides" is an expression often used in referring to "observed tides". [14]
2546	Ocean Station	As defined by the international civil aviation organization, a specifically located area of ocean surface, roughly square and 200 nautical miles on a side. An ocean station vessel on patrol is said to be 'on station' when it is within the perimeter of the area. [14]
2547	Offshore Wind	Wind blowing from the land toward the sea. See land breeze. [14]
2548	Outer Harbour	See harbor. [14]
2549	Picture Plane	A plane upon which a system of lines or rays from an object to form an image or picture can be projected. In perspective drawing, the system of rays is understood to converge to a single point. In photogrammetry, the photograph is the picture plane. [14]
2550	Pointing Line	See collimation: line of. [14]
2551	Pressure Wave	A short-period oscillation of pressure such as that associated with the propagation of sound through the atmosphere; a type of longitudinal wave. [14]
2552	Radio Bearing	See bearing. [14]
2553	Radio Compass	See radio direction finder. [14]
2554	Relative Tilt	See tilt. [14]
2555	Return Period	(Also called recurrence interval.) The average time until the next occurrence of a defined event. When the time to the next occurrence has a geometric distribution, the return period is equal to the inverse of probability of the event occurring in the next time period, that is, T = 1/P, where T is the return period, in number of time intervals, and P is the probability of the next event's occurrence in a given time interval. [4]
2556	Reverberation	Continuation of radiant energy, particularly sound by multiple reflection. Sound scattered towards the source, principally from the ocean surface (surface reverberation) or bottom (bottom reverberation), and from small scattering sources in the medium such as bubbles of air and sus-pended solid matter (volume reverberation). [14]
2557	Rotary Stream	See current: rotary. [14]
2558	Shaded Relief	See illuminated relief. [14]
2559	Shore Station	See fixed station. [14]
2560	Shoreline Map	Shoreline maps are the graphic representation of plane table and photogrammetric surveys. The maps contain graphic data relating to the shoreline, alongshore natural and manmade features, and a narrow zone of natural and manmade features inland from the shoreline. The original sources of a shoreline map are ground survey data and photographs. Utilizing these sources, photogrammetric map compilation techniques, and instruments, cartographers generate shoreline maps, overlays, and associated data. The data are primarily generated to support nautical chart maintenance, new nautical chart construction, and hydrographic survey operations. [14]
2561	Side Echo(Es)	See echo(es): false. [14]
2562	Sidereal Year	See year. [14]
2563	Slave Station	In a radio navigation system, the transmitting station controlled or triggered by the signal received from the master station. Often shortened to slave. [14]
2564	Solar Eclipse	See eclipse. [14]
2565	Sound Channel	The region in the water column where sound velocity first decreases to a minimum value with depth and then increases in value as a result of pressure. Above the minimum value sound rays are bent downward, and below the minimum value sound rays are bent upward; the rays are thus trapped in this channel. Sound travelling in a deep channel can be detected thousands of miles from the sound source. [14]
2566	Sounding Book	See sounding record. [14]
2567	Sounding Lead	A lead used for determining depth of water. Also referred to as plummet. [14]
2568	Sounding Mark	(British terminology). A mark erected for control of sounding; its position is determined by plotting using intersections from sextant fixes. [14]
2569	Sounding Wire	A wire used with a sounding machine in determining depth. [14]
2570	Speed Of Lens	See aperture: relative. [14]
2571	Squaring Down	See squares: method of. [14]
2572	Station Error	See deflection of the vertical. [14]
2573	Swinging Buoy	See compass adjustment buoy. [14]
2574	Synoptic Hour	Hour, expressed in terms of ut, at which, by international agreement, meteorological observations are made simultaneously throughout the globe. [14]
2575	Tracing Cloth	A fine semitransparent linen or cotton cloth sized on one side and dull on the other. [14]
2576	Tropical Wave	A migratory wavelike disturbance in the tropical easterlies. Tropical waves occasionally intensify into tropical cyclones. They are also called easterly waves. [1]
2577	Trunnion Axis	See axis: horizontal. [14]
2578	Two-Way Route	A route within defined limits inside which two-way traffic is established, aimed at providing safe passage of ships through waters where navigation is difficult or dangerous. [14]
2579	Upper Transit	See meridian transit. [14]
2580	Vertical Axis	See axis. [14]
2581	Virtual Image	See image. [14]
2582	Wind Velocity	See wind vector. [14]
2583	Wire Sounding	See sounding. [14]
2584	Air Photograph	See photograph: aerial. [14]
2585	Air Pollutants	Solid, liquid, or gaseous airborne substances that occur in concentrations high enough to threaten the health of people and animals, to harm vegetation and structures, or to toxify a given environment. [1]
2586	Arm Of The Sea	A narrow portion of the sea projecting from the main body. The expression is often shortened to 'arm'. [14]
2587	Audiofrequency	A frequency within the audible range, about 20 to 20.000 cycles per second. Also called sonic frequency. [14]
2588	Azimuth Circle	See bearing circle. [14]
2589	Base Apparatus	Any apparatus designed for use in measuring with accuracy and precision the length of a base in triangulation, or the length of a line in traverse. [14]
2590	Bearing: Rhumb	The direction of a rhumb line through two terrestrial points expressed as angular distance from a reference direction. Also called Mercatorial (or Mercator) bearing. [14]
2591	Brackish Water	Water in which salinity values range from approximately 0.50 to 17.00 parts per thousand. [14]
2592	Camera Station	See air station. [14]
2593	Change Of Tide	A reversal of the direction of motion (rising or falling) of a tide. The expression is also sometimes applied to a reversal in the set of a tidal current. Also called turn of the tide. See also stand of tide. [14]
2594	Coplane: Basal	In photogrammetry, the condition of exposure of a pair of photographs in which the two photographs lie in a common plane parallel to the air base. If the air base is horizontal, the photographs are said to be exposed in horizontal coplane. [14]
2595	Dip Correction	That correction to sextant altitude due to the dip of the horizon. Also called height of eye correction. [14]
2596	Drying Heights	Heights above sounding datum, of any areas (banks, foreshores, rocks, etc.) Which dry at low water. [14]
2597	Eddy Viscosity	The turbulent transfer of momentum by eddies giving rise to an internal fluid friction, in a manner analogous to the action of molecular viscosity in laminar flow, but taking place on a much larger scale. The value of the coefficient of eddy viscosity is of the order 104 square centimeters per second. [14]
2598	Entrance Pupil	The image of the aperture stop formed by all the lens elements on the object side of the aperture stop. [14]
2599	Error Equation	See equation. [14]
2600	External Error	See error: theoretical. [14]
2601	Fiducial Marks	In photogrammetry, index marks, usually four, which are rigidly connected with the camera lens through the camera body and which form images on the negative and usually define the principal point of the photograph. Also marks, usually four in number, in any instrument, which define the axes whose intersection fixes the principal point of a photograph and fulfills the requirements of interior orientation. In surveying, an index line or point. A line or point used as a basis of reference. [14]
2602	Fishing Ground	A water area in which fishing is frequently carried on. Also called fishing area or fishing zone. [14]
2603	Fixed Platform	See fixed station. [14]
2604	Floating Point	In computer systems the type of numeric data approximately representing real numbers. A floating point number is composed of an exponent and a mantissa specifying the numerical value relative to the exponent. Owing to the limited length of a computer word, the floating point representation may cause a loss of precision. [14]
2605	Freezing Point	Temperature of solidification of a liquid in given conditions. [14]
2606	Friction Layer	Atmospheric layer extending from the earth's surface and of depth about 600 to 800 m, within which air motion is affected significantly by surface friction. Above this layer lies the 'free atmosphere'. [14]
2607	Global Warming	Increasing global surface air temperatures that show up in the climate record. The term global warming is usually attributed to human activities, such as increasing concentrations of greenhouse gases from automobiles and industrial processes, for example. [1]
2608	Greenwich Time	See time. [14]
2609	Heeling Magnet	A permanent magnet placed vertically in a tube under the center of a marine magnetic compass, to correct for heeling error. [14]
2610	Hertzian Waves	See wave(s): radio. [14]
2611	Holding Ground	An expression usually used with a modifying adjective to indicate the quality of the holding power of the material constituting the bottom of an anchorage; e.g., of good (or poor) holding ground. [14]
2612	Index Contours	Certain contour lines (usually every fifth) accentuated by use of a line heavier than the intervening ones. [14]
2613	List Of Lights	A publication tabulating navigational lights, with their locations, candle powers, characteristics, etc. To assist in their identification, and details of any accompanying fog signal. A list of lights may contain other information useful to a navigator. Also called light list. [14]
2614	Local Meridian	See meridian. [14]
2615	Longitude Line	A line of position extending in a generally north-south direction. [14]
2616	Luminous Range	See range. [14]
2617	Marine Sextant	See sextant. [14]
2618	Mass Transport	In oceanography, the voluminous transfer of water from one region to another. [14]
2619	Master Compass	See compass. [14]
2620	Masthead Angle	The vertical angle subtended by a ship's mast. [14]
2621	Modulated Wave	See wave. [14]
2622	Month: Nodical	The interval of time between two successive passages of the moon through the same node of its orbit. The length of the nodical month averages 27.21222 mean solar days. Also called draconic month. [14]
2623	Mountain Range	A line of mountains. Also referred to as range of mountains. [14]
2624	Neap Low Water	See mean low water neaps. [14]
2625	Photosynthesis	The formation of carbohydrates in living plants from water and carbon dioxide, by the action of sunlight on the chlorophyll. [14]
2626	Polar Distance	Angular distance from a celestial pole; the arc of an hour circle between a celestial pole, usually the elevated pole, and a point on the celestial sphere, measured from the celestial pole through 180°. When the declination and latitude are of the same name, codeclination is the same as polar distance measured from the elevated pole. [14]
2627	Position Angle	See parallactic angle. [14]
2628	Prime Meridian	See meridian. [14]
2629	Probable Error	See error. [14]
2630	Range: Diurnal	The difference in height between mean higher high water and mean lower low water. Also called great diurnal range. [14]
2631	Reference Mark	In surveying, a supplementary mark of permanent character close to a station or to a base terminal, to which it is related by an accurately measured distance and direction, and/or a difference in elevation. [14]
2632	Reference Tape	A base tape employed solely for use as a standard of comparison. Also called standard tape. [14]
2633	Relative Speed	See relative movement. [14]
2634	Remote Sensing	The measurement or acquisition of information of some property of an object or phenomenon by a recording device that is not in physical or infinite contact with the object or phenomenon under study. Sometimes restricted to the practice of data collection in the wavelengths from ultraviolet to radio regions. [14]
2635	Residual Error	See error. [14]
2636	Safety Fairway	An area within which permits are not granted for the erection of oil or gas related structures. The use of a safety fairway is not usually mandatory, but is recommended. [14]
2637	Satellite Boat	A subsidiary boat used in parallel sounding. [14]
2638	Scale Parallel	Used in Mercator projection charts to indicate the parallel at which the noted scale of the chart is exact. The scale parallel itself need not necessarily be depicted within the chart. [14]
2639	Secondary Port	See station: subordinate. [14]
2640	Semimajor Axis	One-half of the longest diameter of an ellipse. [14]
2641	Semiminor Axis	One-half of the shortest diameter of an ellipse. [14]
2642	Sidereal Month	See month. [14]
2643	Slant Distance	The straight-line distance from one point to another, as contrasted with ground distance. This expression is customarily used only when the straight line connecting the two points lies above the surface of the earth. Also called slant range. [14]
2644	Solar Constant	The rate at which solar energy is received on a surface at the outer edge of the atmosphere perpendicular to the sun's rays when the earth is at a mean distance from the sun. The value of the solar constant is about two calories per square centimeter per minute or about 1376 w/m2 in the si system of measurement. [1]
2645	Sounding Board	See field board. [14]
2646	Source Diagram	A small scale map or index placed on a chart to indicate the coverage area, and textual description, of the source data, used in construction of the chart. Also called compilation diagram. [14]
2647	Speed: Angular	Change of direction per unit time. Also called angular rate or angular velocity. [14]
2648	Spirit Compass	See compass: liquid. [14]
2649	Spot Elevation	A point on a map or chart whose elevation is noted. It is usually indicated by a dot accompanied by a number indicating the vertical distance of the point from the reference datum. Spot elevations are used principally to indicate points higher than their surroundings. Also called spot height. [14]
2650	Transformation	In photogrammetry, the process of projecting a photograph (mathematically, graphically, or photographically) from its plane onto another plane by translation, rotation, and/or scale change. The projection is made onto a plane determined by the angular relations of the camera axes and not necessarily onto a horizontal plane. See also rectification. [14]
2651	Tropical Month	See month. [14]
2652	Vanishing Tide	See tide. [14]
2653	Wave: Standing	A type of wave in which the surface of the water oscillates vertically between fixed points, called nodes, without progression. The points of maximum vertical rise and fall are called antinodes or loops. At the nodes, the underlying water particles exhibit no vertical motion but maximum horizontal motion. At the antinodes the underlying water particles have no horizontal motion and maximum vertical motion. They may be the result of two equal progressive wave trains travelling through each other in opposite directions. Also called stationary wave. [14]
2654	Well: Offshore	A borehole that produces or is capable of producing oil or natural gas. [14]
2655	Acid Deposition	The depositing of acidic particles (usually sulfuric acid and nitric acid) at the earth's surface. Acid deposition occurs in dry form (dry deposition) or wet form (wet deposition). Acid rain and acid precipitation often denote wet deposition. (see acid rain.) [1]
2656	Age Of The Moon	The elapsed time since the last new moon; usually expressed in days and fractions of a day. See phases of the moon. [14]
2657	Aneroid Capsule	Metallic capsule, of thin sides, partially evacuated by a fixed amount, carrying an arrangement to prevent its collapsing under atmospheric pressure, and whose shape changes in accordance with changes of this pressure. [14]
2658	Apparent Motion	See relative motion. [14]
2659	Bathymetric Map	A topographic map of the ocean floor, or the bed of a lake. A topographic chart of the bed of a body of water, or a part of it. Generally, bathymetric maps show depths by contour lines and gradient tints. [14]
2660	Coastal Warning	A navigational warning, or in-force bulletin, promulgated as part of a numbered series by a national coordinator. [14]
2661	Compass Bearing	See bearing. [14]
2662	Contiguous Zone	A zone contiguous to a coastal state's territorial sea, which may not extend beyond 24 nautical miles from the baselines from which the breadth of the territorial sea is measured. The coastal state may exercise certain control in this zone subject to the provisions of international law. [14]
2663	Course Recorder	A device which makes an automatic record of the headings of a vessel. See dead reckoning tracer. [14]
2664	Cust Protractor	See protractor. [14]
2665	Datum: Geodetic	A set of parameters specifying the reference surface or the reference coordinate system used for geodetic control in the calculation of coordinates of points on the earth. Commonly datums are defined as horizontal and vertical datums separately. For a local geodetic datum the reference surface is defined by five parameters: the latitude and longitude of an initial point, the azimuth of a line from this point, and the parameters of the reference spheroid. Absolute datums specify the initial point of the reference ellipsoid to be (ideally) located at the earth's center of mass. For modern reference systems using datum information given by satellites additional parameters are defined, e.g. Gravity models. See also horizontal control datum. [14]
2666	Datum: Sounding	The horizontal plane or tidal datum to which the soundings on a hydrographic survey are reduced. Also called datum for sounding reduction. [14]
2667	Diurnal Current	See current. [14]
2668	Eccentric Angle	See latitude: parametric. [14]
2669	Elevation Tints	See hypsometric tints. [14]
2670	Equal Altitudes	Two altitudes of the same celestial body observed east and then west of the meridian, when it has reached the same value. The expression also applies to the practice, essentially obsolete, of determining the instant of local apparent noon by observing equal altitudes of the sun. [14]
2671	Equisignal Zone	See zone. [14]
2672	Forward Azimuth	See azimuth: geodetic. [14]
2673	Geodetic Survey	See survey. [14]
2674	Gravity Anomaly	The difference between the observed gravity value properly reduced to sea level and the theoretical gravity obtained from gravity formula. See bouguer anomaly, free-air anomaly, isostatic anomaly. [14]
2675	Half Tide Level	The level midway between mean high water and mean low water. It may differ slightly from mean sea level. Also called mean tide level. [14]
2676	Hurricane Watch	A hurricane watch indicates that a hurricane poses a threat to an area (often within several days) and residents of the watch area should be prepared. [1]
2677	Inferior Mirage	See mirage. [14]
2678	Internal Waters	Waters on the landward side of the baseline of the territorial sea and landlocked waters within the state. [14]
2679	Inversion Layer	Atmospheric layer, horizontal or approximately so, in which the temperature increases with increasing height. See temperature inversion. [14]
2680	Irregular Error	See error: accidental. [14]
2681	Laplace Azimuth	See azimuth. [14]
2682	Laplace Station	See station. [14]
2683	Light: Rhythmic	A signal light that shows intermittently, in any given direction, with a regular periodicity. Also referred to as intermittent light. [14]
2684	Linear Parallax	See parallax: absolute stereoscopic. [14]
2685	Local Mean Time	See time. [14]
2686	Luminous Signal	See signal. [14]
2687	Mean Wind Speed	Time-averaged wind speed, averaged over a specified time interval. NOTE The mean wind speed varies with elevation above mean sea level and the averaging time interval; a standard reference elevation is 10 m and a standard time interval is 1 h. See also Sustained Wind Speed and Gust Wind Speed. [15]
2688	Micrometer Comb	A notched scale placed at right angles to the movable wire of a micrometer and so designed that one turn of the micrometer screw will move the micrometer wire across one notch of the comb; the central notch of the comb in conjunction with the zero of the micrometer head furnishes a fiducial point from which all micrometer readings are reckoned. The comb is used for keeping count of whole turns of the micrometer screw, parts of turns being read on the graduated micrometer head. [14]
2689	Minus Soundings	See sounding. [14]
2690	Navarea Warning	A navigational warning or in-force bulletin promulgated as part of a numbered series by a navarea co-ordinator. [14]
2691	Neap High Water	See mean high water neaps. [14]
2692	Normal Equation	See equation. [14]
2693	Numerical Scale	See scale: natural. [14]
2694	Perspective Ray	A line joining a perspective center and a point object. [14]
2695	Phototheodolite	A ground-survey instrument combining a theodolite and a surveying camera in which the relation-ship between the camera axis and the line of collimation of the theodolite can be measured. [14]
2696	Polyvinyl Corer	See corer: hydroplastic. [14]
2697	Position Circle	See circle of position. [14]
2698	Progress Sketch	A map or sketch showing work accomplished. In triangulation and traverse, each point established is shown on the progress sketch as well as lines observed over and bases measured. In a levelling survey, the progress sketch shows the route followed and the towns passed through, but not necessarily the locations of the bench marks. [14]
2699	Radar Altimeter	See altimeter: radio. [14]
2700	Radio Altimeter	See altimeter. [14]
2701	Rainfall Amount	Thickness of the layer of water which accumulates on a horizontal surface, as the result of one or more falls of precipitation, in the absence of infiltration or evaporation, and if any part of the precipitation falling as snow or ice were melted. Also called amount of precipitation. [14]
2702	Range: Luminous	The greatest distance at which a light can be seen merely as a function of its luminous intensity, the meteorological visibility, and the sensitivity of the observer's eye. [14]
2703	Recurrence Rate	See repetition rate. [14]
2704	Reference Plane	See datum: chart, and datum: vertical control. [14]
2705	Reference Point	Any point which can serve as a reference or base for the measurement of other quantities. Also called datum point. [14]
2706	Reflected Light	The process whereby a surface turns back a portion of the radiation that strikes it. When the radiation that is turned back (reflected) from the surface is visible light, the radiation is referred to as reflected light. See reflection. [1]
2707	Reported Danger	An object dangerous to navigation which is shown on a chart but the existence of which has not been confirmed. Sometimes called vigia. [14]
2708	Restricted Area	A specified area designated by appropriate authority within which access or navigation is restricted in accordance with certain specified conditions. [14]
2709	Right Ascension	Angular distance east of the vernal equinox; the arc of the celestial equator, or the angle at the celestial pole, between the hour circle of the vernal equinox and the hour circle of a point on the celestial sphere, measured eastward from the hour circle of the vernal equinox through 24 hours. [14]
2710	Routeing System	Any system of one or more routes or routing measures aimed at reducing the risk of casualties; it includes traffic separation schemes, two-way routes, recommended tracks, areas to be avoided, inshore traffic zones, roundabouts, precautionary areas and deep-water routes. [14]
2711	Sea Level Datum	A determination of mean sea level that has been adopted as a standard datum of heights although it may differ from a later determination over a longer period of time. [14]
2712	Subastral Point	See substellar point. [14]
2713	Subsurface Mark	See underground mark. [14]
2714	Supercell Storm	A severe thunderstorm that consists primarily of a single rotating updraft. Its organized internal structure allows the storm to maintain itself for several hours. Supercell storms can produce large hail and dangerous tornadoes. [1]
2715	Superior Mirage	A refraction phenomenon that makes an object appear to be displaced from its true position. When an object appears higher than it actually is, it is called a superior mirage. When an object appears lower than it actually is, it is an inferior mirage. See mirage. [1]
2716	Three-Point Fix	See fix. [14]
2717	Tidal Constants	Tidal relations that remain essentially constant for any particular locality. Tidal constants are classed as harmonic and non-harmonic, the harmonic constants consisting of the amplitudes and epochs, and the non-harmonic constants including those values determined directly from observations, such as tidal ranges and intervals. [14]
2718	Track Made Good	See track. [14]
2719	Tracking Camera	See camera: ballistic. [14]
2720	Transition Zone	The water area between two opposing currents manifested by eddies, upwelling, rips, and similar turbulent conditions occurring either vertically or horizontally; or a zone between two water masses of differing physical characteristics such as temperature and/or salinity. [14]
2721	Transverse Wave	See wave. [14]
2722	Travelling Wave	See wave: progressive. [14]
2723	Trochoidal Wave	See wave. [14]
2724	True Solar Time	See time: apparent solar. [14]
2725	Variation: Grid	Angular difference in direction between grid north and magnetic north. It is measured east or west from grid north. Also called grivation, or grid magnetic angle. [14]
2726	Wave Refraction	See refraction of water waves. [14]
2727	Wave: Modulated	A wave which varies in some characteristic in accordance with the variations of a modulating wave. See wave: continuous. [14]
2728	Winter Solstice	Approximately December 21 in the northern hemisphere when the sun is lowest in the sky and directly overhead at latitude 231d2°s, the tropic of Capricorn. [1]
2729	Angular Parallax	See parallactic angle. [14]
2730	Angular Velocity	See speed: angular. [14]
2731	Assumed Position	See position. [14]
2732	Astro-Navigation	See navigation: celestial. [14]
2733	Benthic Division	In the classification of the marine environment and its inhabitants, a primary division of the sea which includes all of the ocean floor. The other primary division of the sea is the pelagic division. [14]
2734	Binocular Vision	Simultaneous vision with both eyes. [14]
2735	Compass Meridian	See meridian. [14]
2736	Compass Repeater	A device for repeating at a distance the indications of the master compass. [14]
2737	Continental Rise	a gentle slope rising from the oceanic depths towards the foot of a continental slope. [14]
2738	Conversion Angle	See arc to chord correction. [14]
2739	Conversion Scale	A scale for the conversion of units of one measurement to equivalent units of another measurement. See nomogram. [14]
2740	Conversion Table	A table for the conversion of units of one measurement to equivalent units of another measurement. See nomogram. [14]
2741	Corrector Magnet	See compensator: magnetic. [14]
2742	Course Made Good	The actual track made good over the ground (seabed); the direction of the point of arrival from the point of departure. Course made good is the direction component of the resultant ship's velocity and the water current. Course made good should not be confused with heading, or ship's head. [14]
2743	Deep Ocean Floor	The surface lying at the bottom of the deep ocean. [14]
2744	Depth Of The Sea	The vertical distance from the water surface to the sea bottom. [14]
2745	Digital Computer	See computer. [14]
2746	Diurnal Parallax	See parallax. [14]
2747	Duration Of Fall	See duration of rise and fall. [14]
2748	Electronic Chart	A very broad term to describe the data, the software, and sometimes the electronic system, capable of displaying chart information. [14]
2749	Exposure Station	See air station. [14]
2750	Fixed Angle Plot	(British terminology). Plot prepared in advance for use in normal sounding in lieu of a station pointer. The arcs of equal angle subtended by selected marks are drawn on the sounding board at convenient intervals depending on the scale. The observed sextant angles can then be plotted in the field by visual inspection. See also circle sheet, and sounding: fixed angle. [14]
2751	Geodetic Azimuth	See azimuth. [14]
2752	Geodetic Control	See control. [14]
2753	Graduation Error	See error of graduation. [14]
2754	Grid Coordinates	See coordinates. [14]
2755	Half Convergency	See arc to chord correction. [14]
2756	Hygrothermograph	Instrument resulting from the combination of a thermograph and a hygrograph and furnishing, on the same diagram, simultaneous time recording of atmospheric temperature and humidity. Also called thermohygrograph. [14]
2757	Inferior Transit	See meridian transit. [14]
2758	Initial Meridian	See meridian. [14]
2759	Inland Ice Sheet	An ice sheet of considerable thickness and more than about 50,000 sq. Km in area, resting on rock. Inland ice sheets near sea level may merge into ice shelves. [14]
2760	Intercept Method	See marcq st. Hilaire method. [14]
2761	Local Attraction	Local magnetic disturbance. Also deflection of the plumb line due to a mountain or other irregularity in earth's crust. [14]
2762	Magnetic Anomaly	See local magnetic disturbance. [14]
2763	Magnetic Bearing	See bearing. [14]
2764	Magnetostriction	The phenomenon wherein ferromagnetic material experience an elastic strain when subjected to an external magnetic field. Also, the converse phenomenon in which mechanical stresses cause a change in the magnetic induction of a ferromagnetic material. [14]
2765	Meridian Passage	See meridian transit. [14]
2766	Meridional Parts	The length of the arc of a meridian between the equator and a given parallel on a Mercator chart, expressed in units of 1 minute of longitude at the equator. [14]
2767	Nautical Almanac	See almanac. [14]
2768	Navigation: Land	Navigation of vehicles across land or ice. The expression is generally used in connection with the crossing of a region devoid of roads or landmarks, so that methods similar to those employed in air or marine navigation must be employed. [14]
2769	Navigational Aid	(US Terminology). An instrument, device, chart, method, etc., intended to assist in the navigation of a craft. An aid to navigation is a navigational aid but the latter expression should not be confused with the former which refers only to devices external to a craft. [14]
2770	Neritic Province	See pelagic division. [14]
2771	Oceanic Province	See pelagic division. [14]
2772	Optical Parallax	See parallax: instrumental. [14]
2773	Photograph Nadir	See nadir. [14]
2774	Rational Horizon	See horizon: celestial. [14]
2775	Residual Current	Part of the total current that is not constituted from harmonic tidal components (i.e. the tidal stream). NOTE Residual currents are caused by a variety of physical mechanisms and comprise a large range of natural frequencies and magnitudes in different parts of the world. [15]
2776	Responder Beacon	See transponder beacon. [14]
2777	Small Correction	(British terminology). Minor corrections made to the chart plates. They have been discontinued since 1954. [14]
2778	Spherical Excess	The amount by which the sum of the three angles of a spherical triangle exceeds 180°. [14]
2779	Spheroid: Oblate	An ellipsoid of revolution, the minor axis of which is the axis of revolution. The earth is approximately an oblate spheroid. [14]
2780	Spirit Levelling	See levelling. [14]
2781	Static Stability	See stability. [14]
2782	Subpolar Climate	A climate observed in the northern hemisphere that borders the polar climate. It is characterized by severely cold winters and short, cool summers. Also known as taiga climate and boreal climate. [1]
2783	Subtropical High	A semipermanent high in the subtropical high-pressure belt centered near 30° latitude. The Bermuda high is located over the Atlantic Ocean off the east coast of north america. The pacific high is located off the west coast of north america. [1]
2784	Sulfate Aerosols	Tiny suspended solid particles (dust, smoke, etc.) Or liquid droplets that enter the atmosphere from either natural or human (anthropogenic) sources, such as the burning of fossil fuels. Sulfur-containing fossil fuels, such as coal, produce sulfate aerosols. See aerosols. [1]
2785	Survey: Geodetic	A survey in which the figure and size of the earth is considered. It is applicable for large areas and long lines and is used for the precise location of basic points suitable for controlling other surveys. [14]
2786	Tidal Difference	Difference in time or height of a high or low water at a subordinate station and at a reference station for which predictions are given in the tide tables. The difference, when applied according to sign to the prediction at the reference station, gives the corresponding time or height for the subordinate station. [14]
2787	Vibrating Needle	A magnetic needle used in compass adjustment to find the relative intensity of the horizontal components of the earth's magnetic field and the magnetic field at the compass location. Also called horizontal force instrument. See compensation of magnetic compass. [14]
2788	Water Equivalent	The depth of water that would result from the melting of a snow sample. Typically about 10 inches of snow will melt to 1 inch of water, producing a water equivalent of 10 to 1. [1]
2789	Wave: Continuous	A series of waves of like amplitude and frequency. See wave: modulated, pulse. [14]
2790	Weather Elements	The elements of air temperature, air pressure, humidity, clouds, precipitation, visibility, and wind that determine the present state of the atmosphere, the weather. [1]
2791	Well: Production	A borehole, producing oil or natural gas, which is covered by a seabed installation of valves and pipelines for the controlled removal of the product. See also sub-sea completion. [14]
2792	Wind Circulation	The flow of air through a given area. [14]
2793	Adiabatic Process	A thermodynamic change of state of a system in which there is no transfer of heat or mass across the boundaries of the system. In an adiabatic process, compression always results in warming, expansion in cooling. [14]
2794	Aneroid Barometer	An instrument designed to measure atmospheric pressure. It contains no liquid. [1]
2795	Annual Aberration	See aberration of light. [14]
2796	Anomalistic Month	See month. [14]
2797	Bilby Steel Tower	A demountable and transportable triangulation tower for elevating a theodolite and luminous signals above the ground, designed by j.s. Bilby, usc&gs. [14]
2798	Centrifugal Force	The force with which a body moving under constraint along a curved path reacts to the constraint. Equal and opposite to the centripetal force. [14]
2799	Collimation Error	See error of collimation. [14]
2800	Compass Corrector	See compensator: magnetic. [14]
2801	Compass: Steering	The compass placed next to the steering wheel, by which the course is steered. See also steering repeater. [14]
2802	Computer Graphics	All methods and techniques used in computer sciences to represent data in graphical form and to process images. [14]
2803	Controlled Mosaic	See mosaic. [14]
2804	Current Direction	See direction of current. [14]
2805	Daily Retardation	The amount of time by which corresponding tidal phases grow later day by day (averages approximately 50 minutes). [14]
2806	Datum For Heights	See datum: vertical control. [14]
2807	Discoloured Water	Unnatural coloured areas in the sea due to the existence of shoals. Sea water having a colour other than the blues and greens normally seen. Variations of the colors red, yellow, green and brown, as well as black and white, have been reported. Discolorations may appear in patches, streaks, or large areas and may be caused by concentrations of inorganic or organic particles or plankton. See red tide. [14]
2808	False Coordinates	See coordinates. [14]
2809	Field Examination	A special purpose hydrographic, wire drag, or side scan sonar survey of very limited area; i.e., usually an investigation of one or more individual and scattered items. [14]
2810	Geodetic Parallel	See parallel. [14]
2811	Ground Photograph	See photograph: terrestrial. [14]
2812	Horizon: Apparent	The irregular line along which rays from the point of observation are tangent to the surface of the earth. Also called visible (or local) horizon. [14]
2813	Hyperbolic System	Radiolocation system supplying hyperbolic lines of position. [14]
2814	Indian Tide Plane	See indian spring low water. [14]
2815	Induced Magnetism	See magnetism. [14]
2816	Intersected Point	See station: intersection. [14]
2817	Logarithmic Scale	See scale. [14]
2818	Longshore Current	A current paralleling the shore largely within the surf zone. It is caused by the excess water brought to the zone by the small net mass transport of wind waves. Longshore currents feed into rip currents. [14]
2819	Magnetic Meridian	See meridian. [14]
2820	Meridian Altitude	See altitude. [14]
2821	Meridian Distance	In astronomy, the hour angle of a celestial body when close to but not exactly on the astronomical meridian. In plane surveying, the perpendicular distance in a horizontal plane of a point from a meridian of reference. [14]
2822	Negative Altitude	See angle of depression. [14]
2823	No Anchoring Area	A routing measure comprising an area within defined limits where anchoring is hazardous or could result in unacceptable damage to the marine environment. Anchoring in a no anchoring area should be avoided by all ships or certain classes of ships, except in case of immediate danger to the ship or the persons on board. [14]
2824	Nyquist Frequency	The highest frequency that may be uniquely resolved in a time series from a given sampling interval. The nyquist frequency is equal to twice the sampling interval. Analyzing frequencies for which the nyquist criterion is not met leads to aliasing. [14]
2825	Observed Altitude	See altitude. [14]
2826	Personal Parallax	See parallax: instrumental. [14]
2827	Perspective Plane	Any plane containing the perspective center. The intersection of a perspective plane and the ground will always appear as a straight line on an aerial photograph. [14]
2828	Plane Coordinates	See coordinates: plane rectangular. [14]
2829	Point Of Symmetry	The point in the focal plane of a camera about which all lens distortions are symmetrical. If the lens were perfectly mounted, the point of symmetry would coincide with the principal point. [14]
2830	Polar Coordinates	See coordinates. [14]
2831	Positive Altitude	See angle of elevation. [14]
2832	Radiative Forcing	An increase (positive) or a decrease (negative) in net radiant energy observed over an area at the tropopause. An increase in radiative forcing may induce surface warming, whereas a decrease may induce surface cooling. [1]
2833	Recommended Track	A route which has been specially examined to ensure so far as possible that it is free of dangers and along which, ships are advised to navigate. [14]
2834	Relative Humidity	The ratio of the actual vapor pressure to the vapor pressure corresponding to saturation at the prevailing temperature. [14]
2835	Run Of Micrometer	See error of run. [14]
2836	Spheroid: Prolate	An ellipsoid of revolution, the major axis of which is the axis of revolution. [14]
2837	Spirit Level Axis	See axis of spirit level. [14]
2838	Spring High Water	See mean high water springs. [14]
2839	Tidal Constituent	also known as a Constituent Tide; One of the harmonic elements in a mathematical expression for the tide-producing force and in corresponding formulas for the tide or tidal current. Each constituent represents a periodic change or variation in the relative positions of the Earth, Moon and Sun. [21]
2840	Tidal Constituent	See harmonic constituent. [14]
2841	Velocity Of Sound	See sound velocity. [14]
2842	Angle Of Elevation	The angle in the vertical plane between the horizontal and the line to an object above the horizon. Also called positive altitude. [14]
2843	Apparent Shoreline	The seaward limit of marine vegetation, such as mangrove, marsh grass, or trees in water that would reasonably appear to the mariner from a distance to be the fast shoreline. The seaward limit of kelp, low grass in water, and other low ‘lying vegetation normally does not constitute an apparent shoreline. A line drawn on the chart in lieu of the mean high-water line or the mean water level line in areas where either may be obscured by marsh, mangrove, cypress, or other type of marine vegetation. This line represents the intersection of the appropriate datum with the outer limits of vegetation and appears to the navigator as shoreline. [14]
2844	Archipelagic State	A state constituted wholly by one or more archipelagos, eventually including other islands. [14]
2845	Artificial Horizon	See horizon. [14]
2846	Celestial Latitude	See latitude. [14]
2847	Centre Of Buoyancy	See buoyancy. [14]
2848	Compass Adjustment	See compensation of magnetic compass. [14]
2849	Compressional Wave	See wave. [14]
2850	Cooling Degree-Day	A form of degree-day used in estimating the amount of energy necessary to reduce the effective temperature of warm air. A cooling degree-day is a day on which the average temperature is one degree above a desired base temperature. [1]
2851	Coordinates: False	Grid coordinates obtained by adding fixed numerical quantities to all grid values. These quantities are so large that none of the resultant false coordinates are negative. Such a procedure introduces a false origin to the south and west of the true origin. See coordinates: origin of. [14]
2852	Coordinates: Plane	See coordinates: plane rectangular. [14]
2853	Diurnal Aberration	See aberration of light. [14]
2854	Eyepiece: Erecting	An eyepiece containing an auxiliary re-imagining system of one or two lenses which inverts the primary image before it reaches the eyepiece proper. The device is now obsolescent, the inversion being performed by prism systems. Also called inverting eyepiece. [14]
2855	Fundamental Circle	See primary great circle. [14]
2856	Geometric Latitude	See latitude: parametric. [14]
2857	Great Circle Track	See track. [14]
2858	Gyroscopic Compass	See compass. [14]
2859	Gyroscopic Inertia	The property of a gyroscope of resisting any force which tends to change its axis of rotation. A gyroscope tends to maintain the direction of its axis of rotation in space. [14]
2860	Hand Lead Sounding	See sounding. [14]
2861	Harmonic Constants	The amplitude and epochs of the harmonic constituent of the tide, or tidal current at any place. [14]
2862	Horizontal Control	See control. [14]
2863	Illuminated Relief	The representation of relief with the appearance of lighting from one or more directions, giving a three-dimensional impression. Also called shaded relief. [14]
2864	Isometric Parallel	See parallel. [14]
2865	Large Scale Survey	See survey. [14]
2866	Latitude: Geodetic	The angle which the normal at a point on the spheroid makes with the plane of the geodetic equator. [14]
2867	Lithographic Image	An ink-receptive image on the lithographic press plate, either photographic or direct hand or transfer image. The design or drawing on stone or metal plate. [14]
2868	Magnetic Deviation	See deviation. [14]
2869	Magnetic Intensity	See magnetic field intensity. [14]
2870	Micrometer: Ocular	A filar micrometer so placed that its wire moves in the principal focal plane of a telescope. Also called an eyepiece micrometer. [14]
2871	Nautical Astronomy	See astronomy. [14]
2872	Orientation: Basal	In photogrammetry, the establishment of the position of both ends of an air base with respect to a ground system of coordinates. In all, six elements are required. These are essentially the three-dimensional coordinates of each end of the base. [14]
2873	Position: Detached	In hydrographic survey, an expression indicating a position taken, to locate rocks, floating aids to navigation, least depths on shoals or other dangers or features of importance. [14]
2874	Preliminary Survey	See survey: reconnaissance. [14]
2875	Principal Parallel	See parallel: photograph. [14]
2876	Reciprocal Bearing	See bearing. [14]
2877	Resonant Frequency	See frequency. [14]
2878	Shallow Water Wave	See wave: transitional water. [14]
2879	Sonic Depth Finder	See echo sounder. [14]
2880	Static Instability	See instability. [14]
2881	Stereoscopic Image	The mental impression of a three-dimensional model which results from viewing two overlapping perspective views. Also called stereoscopic model or stereo model. [14]
2882	Tape Correction(S)	Corrections applied to a distance measured with a tape to eliminate errors caused by the physical condition of the tape, and to the manner in which it is used. [14]
2883	Tidal Observations	See observation. [14]
2884	Topographic Signal	See signal. [14]
2885	Track: Recommended	A track, shown on a chart by either a dashed or a continuous line, recommended to all or only certain vessels. [14]
2886	Transit Instrument	See transit. [14]
2887	Transit Micrometer	See micrometer. [14]
2888	Transponder Beacon	A beacon having a transponder. Also called responder beacon. [14]
2889	Unit Magnetic Pole	In magnetic theory, a fictitious entity analogous to a unit electric charge in electrostatic theory. [14]
2890	Aeronautical Beacon	See beacon. [14]
2891	Angle Of Depression	The angle in the vertical plane between the horizontal and the line to an object below the horizon. Also called negative altitude. [14]
2892	Angle Of Reflection	The angle between the line of motion of a reflected ray and the perpendicular to a surface at the point of reflection. [14]
2893	Apparent Solar Time	See time. [14]
2894	Broadcast Ephemeris	Ephemeris transmitted by a satellite which describes its position and orbital parameters. [14]
2895	Celestial Longitude	See longitude. [14]
2896	Condensation Nuclei	Also called cloud condensation nuclei. Tiny particles upon whose surfaces condensation of water vapor begins in the atmosphere. [1]
2897	Depth Anomaly Graph	A graph constructed to determine the difference between the computed or thermometric depth and the ideal or assumed depth of reversal of thermometers attached to a nansen bottle. [14]
2898	Ekman Current Meter	A widely used instrument for measuring the speed and direction of the current at any depth. It is designed for use from a ship or boat at anchor when the stream does not attain a rate of more than 3 to 3 1/2 knots. [14]
2899	Error: Polarization	Error in a radio bearing or the course indicated by a radio beacon, due to horizontally-polarized components of the electric field under certain transmission conditions. The terms night error or night effect have become obsolete. [14]
2900	Great Circle Course	See course. [14]
2901	High Water Interval	See lunitidal interval. [14]
2902	Hydrographic Signal	See signal. [14]
2903	Instability: Static	State of hydrostatic equilibrium of the atmosphere in which a particle of air moved from its initial level undergoes a hydrostatic force which tends to remove it further from this level. Also called hydrostatic instability. [14]
2904	Local Apparent Time	See time. [14]
2905	Longitude: Geodetic	The angle between the plane of the geodetic meridian and the plane of an initial meridian, arbitrarily chosen. [14]
2906	North Magnetic Pole	See magnetic pole. [14]
2907	Offshore Navigation	See navigation. [14]
2908	Parametric Latitude	See latitude. [14]
2909	Permanent Magnetism	See magnetism. [14]
2910	Photograph Meridian	See meridian. [14]
2911	Photograph Parallel	See parallel. [14]
2912	Radio Range Station	A radio navigation land station in the aeronautical radio navigation service providing radio equisignal zones. In certain instances a radio range station may be placed aboard a ship. [14]
2913	Range Of Visibility	The extreme distance at which an object or light can be seen. See range: geographical, and range: luminous. [14]
2914	Reference Ellipsoid	See reference spheroid. [14]
2915	Repeatable Accuracy	In a navigation system, the measure of the accuracy with which the system permits the user to return to a position as defined only in terms of the coordinates peculiar to that system. For example, the distance specified for the repeatable accuracy of the system such as loran’s is the distance bet-ween two loran’s positions established using the same stations and time difference readings at different times. The correlation between the geographical coordinates and the system coordinates may or may not be known. [14]
2916	Self-Aligning Level	See levelling instrument: self-aligning level. [14]
2917	Sidereal Hour Angle	See hour angle. [14]
2918	Stereoscopic Fusion	The mental process which combines the two perspective views to give an impression of a three-dimensional model. [14]
2919	Supercell Tornadoes	Tornadoes that occur within supercell thunderstorms that contain well-developed, mid-level mesocyclones. [1]
2920	Surface Temperature	Temperature of the water of the surface layer of the sea (or lake, river, etc.). [14]
2921	Transient Magnetism	See magnetism: temporary. [14]
2922	Triangulation Point	See station: triangulation. [14]
2923	Tropical Rainforest	A type of forest consisting mainly of lofty trees and a dense undergrowth near the ground. [1]
2924	Universal Time (Ut)	Time as defined by the rotational motion of the earth and determined from the apparent diurnal motions which reflect this rotation. Because of variations in the rate of rotation, universal time is not rigorously uniform. Also called Greenwich mean time. [14]
2925	Vertical Collimator	See collimator. [14]
2926	Amplitude Modulation	See modulation. [14]
2927	Azimuthal Projection	See projection. [14]
2928	Compass Compensation	See compensation of magnetic compass. [14]
2929	Conformal Projection	See projection. [14]
2930	Dangerous Semicircle	Region of a tropical cyclone, situated to the right of its path in the northern hemisphere and to the left of its path in the southern hemisphere, in which the seas are higher and the winds more violent and tend also to carry shipping forward on to the cyclone's path. The other half of the cyclone is termed the navigable semicircle. [14]
2931	Dead Reckoning Track	See track. [14]
2932	Direction Of Current	The direction toward which a current is flowing, called the set of the current. Also called current direction. [14]
2933	Direction Of Gravity	See gravity. [14]
2934	Geometric Projection	See projection: perspective. [14]
2935	Great Circle Bearing	See bearing. [14]
2936	Great Circle Sailing	See sailing. [14]
2937	Illuminated Contours	An application of illuminated relief in which contours appear lighter on illuminated slopes and darker on the shadow slopes. [14]
2938	Inferior Conjunction	See conjunction. [14]
2939	International Voyage	A voyage from a country to which the 1974 solas convention applies to a port outside that country or conversely (solas chapter 1, regulation 2d). [14]
2940	Interocular Distance	See interpupillary distance. [14]
2941	Intersection Station	See station. [14]
2942	Latitude: Geocentric	The angle at the center of the earth between the plane of the equator and a line to a point on the surface of the earth. [14]
2943	Lead Line Correction	A correction to be applied to the depths taken with a rope lead line to take into account the shrinking and stretching. This difficulty has been overcome by inserting a wire heart in the rope. [14]
2944	Magnetic Observatory	A place where buildings are equipped for observing temporal changes in the earth's magnetic field. [14]
2945	Magnetic Retentivity	The ability to retain magnetism after removal of the magnetizing force. Also called remanence. [14]
2946	Magnetism: Temporary	Magnetism of craft which changes in amount with every change of heading. Also called transient magnetism. [14]
2947	Nonsupercell Tornado	A tornado that occurs with a cloud that is often in its growing stage, and one that does not contain a midlevel mesocyclone, or wall cloud. Landspouts and gustnadoes are examples of nonsupercell tornadoes. [1]
2948	Operating Conditions	Most severe combination of environmental conditions under which a given operation will be permitted to proceed. NOTE Operating conditions are determined for operations that exert a significant action on the structure. Operating conditions are usually a compromise: they are sufficiently severe that the operation can generally be performed without excessive downtime, but they are not so severe that they have an undue impact on design. [15]
2949	Parallel Of Latitude	See parallel. [14]
2950	Plane Table Traverse	See traverse. [14]
2951	Quadrantal Deviation	See deviation. [14]
2952	Repeating Instrument	See theodolite: repeating. [14]
2953	Saint Hilaire Method	See marcq st. Hilaire method. [14]
2954	Satellite Navigation	A positioning method using satellites. [14]
2955	Terrestrial Meridian	See meridian: astronomical. [14]
2956	Three-Arm Protractor	See protractor: three-arm. [14]
2957	Tropical Wet Climate	A tropical climate with sufficient rainfall to produce a dense tropical rainforest. [1]
2958	Altitude: Ex-Meridian	An altitude of a celestial body near the celestial meridian of the observer, to which a correction is to be applied to determine the meridian altitude. Also called circummeridian altitude. [14]
2959	Face(S) Of Theodolite	Either of the two positions, 'face left' (f.l.) And 'face right' (f.r.) Of the theodolite, when observations are made with the vertical circle on the left or on the right of the telescope respectively. [14]
2960	Hyperbolic Navigation	See navigation. [14]
2961	Leeward Tidal Current	See tide: leeward. [14]
2962	Light Characteristics	See characteristics of light. [14]
2963	List Of Radio Signals	A publication tabulating and combining particulars of: coast radio stations, port radio stations, radio direction finding stations, radio beacons, etc., as well as other information on radio services useful to a navigator. [14]
2964	Long Range Navigation	See navigation. [14]
2965	Magnetic Compensation	See compensation of magnetic compass. [14]
2966	Magnetic Permeability	The property of a magnetizable substance that determines the degree in which it modifies the magnetic flux in the region occupied by it. [14]
2967	Most Probable Maximum	Value of the maximum of a variable with the highest probability of occurring. NOTE The most probable maximum is the value for which the probability density function of the maxima of the variable has its peak. It is also called the mode or modus of the statistical distribution. [15]
2968	Navigational Triangle	See astronomical triangle. [14]
2969	Ocean Weather Station	Station aboard a suitably equipped and staffed ship which tries to maintain a fixed maritime location and which observes and reports for international exchange the observations of specified elements. [14]
2970	Orientation: Interior	In photogrammetry, the determining (analytically or in a photogrammetric instrument) of the interior perspective of the photograph as it was at the instant of exposure. Elements of interior orientation are the calibrated focal length, location of the calibrated principal point, and the calibrated lens distortion. Also called inner orientation. [14]
2971	Quadrantal Correctors	Masses of soft iron placed near a magnetic compass to correct for quadrantal deviation. Spherical quadrantal correctors are called quadrantal spheres. [14]
2972	Spherical Coordinates	See coordinates. [14]
2973	Theodolite: Repeating	A theodolite so designed that successive measures of an angle may be accumulated on the graduated circle, and a final reading of the circle made which represents the sum of the repetitions. The observed value of the angle is obtained by dividing the total arc passed through in making the series of observations by the number of times the angle has been observed. Also called repeating instrument. See repetition method of observation. [14]
2974	Tide-Generating Force	See tide-producing force. [14]
2975	Triangulation: Arc Of	A system of triangulation of limited width designed to progress in a single general direction. Also called chain of triangulation. [14]
2976	Trigonometric Station	See station: triangulation. [14]
2977	Wave: Electromagnetic	Wave(s) of associated electric and magnetic fields characterized by variations of the fields. The electric and magnetic fields are at right angles to each other and to the direction of propagation. An electromagnetic wave is coherent if the phase-time relationship is constant throughout the propagation path. [14]
2978	Automatic Gain Control	A circuit which automatically maintains a constant output volume regardless of input signal strength. Also called automatic volume control. [14]
2979	Design Crest Elevation	Extreme crest elevation measured relative to still water. [14]
2980	Eccentricity Of Circle	The distance between the center of figure of a graduated circle of an instrument and its center of rotation. [14]
2981	Flux-Gate Magnetometer	See magnetometer. [14]
2982	Long-term Distribution	Probability distribution of a variable over a long time scale. NOTE The time scale exceeds the duration of a sea state, in which the statistics are assumed constant (see shortterm distribution in Short-term Distribution). The time scale is hence comparable to a season or to the design service life of a structure. NOTE The time scale exceeds the duration of a sea state, in which the statistics are assumed constant (see shortterm distribution in Short-term Distribution). The time scale is hence comparable to a season or to the design service life of a structure. [15]
2983	Meteorological Element	Atmospheric variable or phenomenon which characterize the state of the weather at a specific place at a given time: air temperature, atmospheric pressure, wind, humidity, thunderstorm, fog, precipi-tation, etc. [14]
2984	Perspective Projection	See projection. [14]
2985	Projection: Equal Area	A projection having a constant area scale. Such a projection is not conformal and is not used for navigation. Also called equivalent projection. [14]
2986	Sonic Line Of Position	A line of position determined by means of sound waves. Also called acoustic line of position. [14]
2987	Station: Triangulation	A recoverable point on the earth, whose geographic position has been determined by angular methods with geodetic instruments. A triangulation station is a selected point, which has been marked with a station mark, or it is a conspicuous natural or artificial object. Also called trigonometric station or triangulation point. [14]
2988	Terrestrial Photograph	See photograph. [14]
2989	Tide(S): Shallow Water	A distortional effect upon astronomically generated tide caused by shallow waters. See also tide(s): quarter-diurnal. [14]
2990	Track Line Of Sounding	A continuous record of soundings obtained by a ship on an extended voyage en route between its home port and the working ground. Also called cruise line of sounding. [14]
2991	Vertical Control Datum	See datum. [14]
2992	Artificial Intelligence	1. The capability of a device to perform functions that are normally associated with human intelligence, such as reasoning, learning, and self ‘improvement. 2. Research and study in methods for the development of a machine that can improve its own operations. The development or capability of a machine that can proceed or perform functions that are normally associated with human intelligence, as learning, adapting, reasoning, self ‘correction, automatic improvement. 3. The study of computer and related techniques to supplement the intellectual capabilities of man. As man has invented and used tools to increase his physical powers, he now is beginning to use artificial intelligence to increase his mental powers. In a more restricted sense, the study of techniques for more effective use of digital computers by improved programming techniques. [14]
2993	Difference Of Longitude	The angle at the pole or intercepted arc of equator between the meridians of two places. [14]
2994	Eccentricity Of Alidade	The distance between the center of figure of the index points of an alidade and the center of figure of the graduated circle. [14]
2995	Electrical Thermometers	Thermometers that use elements that convert energy from one form to another (transducers). Common electrical thermometers include the electrical resistance thermometer, thermocouple, and thermistor. [1]
2996	Equivalent Focal Length	See focal length. [14]
2997	Exclusive Economic Zone	The exclusive economic zone is an area, not exceeding 200 nautical miles from the baselines from which the breadth of the territorial sea is measured, subject to a specific legal regime established in the united nations convention on the law of the sea under which the coastal state has certain rights and jurisdiction. [14]
2998	Geostationary Satellite	A satellite that orbits the earth at the same rate that the earth rotates and thus remains over a fixed place above the equator. [1]
2999	Geostationary Satellite	An earth satellite moving eastward in an equatorial, circular orbit at an altitude (approximately 35,900 kilometers) such that its period of revolution is exactly equal to (synchronous with) the rotational period of the earth. Such a satellite will remain fixed over a point on the earth's equator. Although geostationary satellites are frequently called geosynchronous or synchronous satellites, the orbit of an eastward moving synchronous satellite must be equatorial if the satellite is to remain fixed over a point on the equator. Otherwise, the satellite moves daily in a figure-eight pattern relative to the earth. Also called fixed satellite. [14]
3000	Significant Wave Height	The average height of the one-third highest waves of a given wave group or sample. [9]
3001	Significant Wave Period	Ts ; The significant period is apt to be the average period of all waves whose troughs are below and whose crests are above the mean water level (zero up-crossing method). The significant wave period usually obtained by visual observations of waves is likely to be the average period of 10 to 15 successive prominent waves. [26]
3002	Submarine Sound Channel	A water layer with minimum sound velocity and high concentration of sound energy in which sound waves are propagated without reflection from sea surface or bottom. [14]
3003	Tape: Length Correction	The difference between the nominal length of a tape and its effective length under conditions of standardization. [14]
3004	Kelvin Temperature Scale	Thermodynamic scale of temperature (t°k) defined by assigning to the triple point of pure water, considered as a fundamental fixed point, the temperature of 273.16°k. Also called absolute temperature scale. [14]
3005	Swath(E) Sounding System	A multi-beam system which is capable of obtaining a lane of soundings from a single ship's track. [14]
3006	Celsius Temperature Scale	A thermodynamic scale of temperature (t°c) defined as a function of the kelvin temperature scale (t°k) by the relationship t°c = t°k 273.15. Name for anders celsius (1701-44), swedish astronomer who first described, in 1742, the centigrade temperature scale. Note. According to a resolution of the ninth international conference on weights and measures (1948), temperature should be designated 'degrees Celsius' and the designation 'degrees centigrade' should be discontinued. [14]
3007	Deviation Of The Vertical	See deflection of the vertical. [14]
3008	Harmonic Analysis Of Tide	The mathematical process by which the observed tide at a place is analyzed by breaking it down into a number of constituent tides of simple periodic forces, each having a fixed period. In this process the sun and moon are replaced by a number of hypothetical tide-producing bodies which move in circular orbits around the earth in the plane of the equator. See harmonic constants, harmonic constituent. [14]
3009	Hydrographic Survey Sheet	An inclusive term used to designate both boat sheets and smooth sheets. Also called survey sheet. [14]
3010	International Atomic Time	See atomic time: international. [14]
3011	Meteorological Visibility	See visibility. [14]
3012	Rotating Loop Radiobeacon	See rotating radio beacon station. [14]
3013	Shallow Water Constituent	A short-period harmonic term introduced into the formula of astronomical tide constituents to take account of the change in the form of a tide wave resulting from shallow water conditions. Shallow water constituents include over tides and compound tides. See harmonic constituent. [14]
3014	Traffic Separation Scheme	A routing measure aimed at the separation of opposing streams of traffic by appropriate means and by the establishment of traffic lanes. [14]
3015	Deflection Of The Vertical	The angle at a point on the earth (geoid) between the vertical (direction of the plumb line) and the direction of the normal to the spheroid of reference through the point. Also called deflection of the plumb line, deviation of the vertical, or station error. [14]
3016	Eccentricity Of Instrument	The combination of eccentricity of circle and eccentricity of alidade. The effect of eccentricity of instruments on an observed direction is eliminated by having the verniers or micrometer microscopes, with which the circle is read, spaced at equal distances around the circle. [14]
3017	Underwater Position Fixing	A method of position fixing for surface vessels, submersibles or towed devices in relation to a network of underwater acoustic beacons on the seabed with known relative positions. [14]
3018	Hunter Short Base Apparatus	A base apparatus designed for measuring short bases by the subtended method. It consists of a jointed steel tape made up of four sections suspended in catenary between regularly spaced supports. The hunter short base apparatus may be used over rough ground which is unsuitable for ground taping. [14]
3019	Initial Great Circle Course	See course: great circle. [14]
3020	Error Of Closure Of Triangle	The amount by which the sum of the three observed angles of a triangle fails to equal exactly 180° plus the spherical excess of the triangle. Also referred to as closure of triangle. [14]
3021	Continental (Or Island) Shelf	A zone adjacent to a continent (or around an island), extending from the low water line to the depth at which there is usually a marked increase of slope to greater depth. See shelf.- 2- in UNCLOS article 76:- the continental shelf of a coastal state comprises the sea bed and subsoil of the submarine areas that extend beyond its territorial sea throughout the natural prolongation of its land territory to the outer edge of the continental margin, or to a distance of 200 nautical miles from the baselines from which the breadth of the territorial sea is measured where the outer edge of the continental margin does not extend out to that distance. [14]
3022	Protected Reversing Thermometer	see thermometer. [14]
3023	Equinoctial System Of Coordinates	See celestial equator system of coordinates. [14]
3024	Distance Measuring Equipment (Dme)	See electronic distance measuring equipment. [14]
3025	Duration Of Flood And Duration Of Ebb	Duration of flood is the interval of time in which a tidal current is flooding, and the duration of ebb is the interval in which it is ebbing; these intervals being reckoned from the middle of the intervening slack waters or minimum currents. Together they cover, on an average, a period of 12.42 hours for a semidiurnal tidal current or a period of 24.84 hours for a diurnal current. In a normal semidiurnal tidal current, the duration of flood and duration of ebb will each be approximately equal to 6.21 hours, but the times may be modified greatly by the presence of a non-tidal flow. In a river the duration of ebb is usually longer than the duration of flood because of the fresh water discharge, especially during the spring months when snow and ice melt are the predominant influences. [14]
3026	Duration Of Rise And Duration Of Fall	Duration of rise is the interval from low water to high water, and duration of fall is the interval from high water to low water. Together they cover, on an average, a period of 12.42 hours for a semidiurnal tide or a period of 24.84 hours for a diurnal tide. In a normal semidiurnal tide, the duration of rise and duration of fall will each be approximately equal to 6.21 hours, but in shallow waters and in rivers there is a tendency for a decrease in the duration of rise and a corresponding increase in the duration of fall. [14]
3027	Witness Mark	A mark placed at a known distance and direction from a property corner, base terminal, or survey station, to aid in its recovery and identification. [14]
3028	Absolute Zero	A temperature reading of 2273°c, 2460°f, or 0k. Theoretically, there is no molecular motion at this temperature. [1]
3029	Abyssal Hills	A tract of small elevations on the deep-sea floor. [14]
3030	Active System	Any electromagnetic or sonic position fixing system operating with an interrogation-response procedure. See also passive system. [14]
3031	Advection Fog	Occurs when warm, moist air moves over a cold surface and the air cools to below its dew point. [1]
3032	Ambient Noise	The erratic electromagnetic or sonic background noise emitted by natural or artificial sources contaminating the proper signal. [14]
3033	Angle: Danger	See danger angle. [14]
3034	Angular Speed	See speed. [14]
3035	Arctic Circle	The geographical parallel having a north latitude equal to the complement of the declination of the summer solstice (latitude = 66 deg 33' n approximately). [14]
3036	Astro Compass	See under compass. [14]
3037	Axis: Optical	See axis of lens. [14]
3038	Azimuth: True	Azimuth relative to true north. [14]
3039	Basal Coplane	See coplane: basal. [14]
3040	Basic Control	See control. [14]
3041	Beacon: Radio	See radio beacon. [14]
3042	Bearing Plate	See pelorus. [14]
3043	Bearing: Grid	Bearing relative to grid north. See also azimuth: grid. [14]
3044	Bearing: True	See bearing. [14]
3045	Bowditch Rule	A method of adjustment of traverses. [14]
3046	Bridge: Swing	A movable bridge which rotates in a horizontal plane about a vertical pivot to allow the passage of vessels. [14]
3047	Buoy: Fairway	A buoy intended to be the first to be seen during an approach from the open sea to a fairway. [14]
3048	Buoy: Lateral	A buoy used to indicate a lateral limit of navigable water. [14]
3049	Buoy: Mooring	A buoy secured to the bottom by permanent moorings with means for mooring a vessel by use of its anchor chain or mooring lines. [14]
3050	Buoy: Special	A buoy primarily used to indicate an area or feature referred to in nautical documents rather than to assist navigation. [14]
3051	Cable: Leader	Cable lying on the bottom and carrying an electric current by which ships equipped with appropriate instruments, can be guided. [14]
3052	Calendar Line	See date line. [14]
3053	Cardinal Buoy	See cardinal mark [14]
3054	Cardinal Mark	In the iala maritime buoyage system a navigation mark used in conjunction with the compass to indicate where the mariner may find the best navigable water. It is placed in one of the four quadrants (north, east, south and west) bounded by inter-cardinal bearings from the point marked. [14]
3055	Cellular Wave	See wave. [14]
3056	Celsius Scale	A temperature scale where zero is assigned to the temperature where water freezes and 100 to the temperature where water boils (at sea level). [1]
3057	Chart Reading	Interpretation of the symbols, lines, abbreviations, and terms appearing on charts. May be called map reading when applied to maps generally. [14]
3058	Chart: Marine	See chart: nautical. [14]
3059	Charted Depth	See depth. [14]
3060	Circle: Great	The intersection of a sphere and a plane through its center. See also orthodrome. [14]
3061	Circle: Small	The intersection of a sphere and a plane which does not pass through its center. [14]
3062	Cleared Depth	The effective depth over a feature, obtained by a wire drag survey. [14]
3063	Clearing Line	A straight line, on a chart, that marks the boundary between a safe and a dangerous area; or that passes clear of a navigational danger. Sectors of lighthouse lights are usually bounded by them. [14]
3064	Clock: Atomic	A precision clock that depends for its operation on an electrical oscillator regulated by the natural vibrational frequency of an atomic system (such as a beam). The combination of two (or more) radionuclides whose activities can be utilized to ascertain time intervals. [14]
3065	Clock: Cesium	An atomic clock using the properties of cesium. [14]
3066	Clock: Quartz	See clock: crystal. [14]
3067	Cloud Seeding	The introduction of artificial substances (usually silver iodide or dry ice) into a cloud for the purpose of either modifying its development or increasing its precipitation. [1]
3068	Coastal Chart	See chart: coast. [14]
3069	Coaxial Cable	See cable. [14]
3070	Compass North	See north: compass. [14]
3071	Compass: Boat	A small portable compass mounted in a box for convenient use in small water craft. [14]
3072	Compass: Dumb	See pelorus. [14]
3073	Constellation	Formerly a number of fixed stars grouped within an imaginary outline. Now, a region of the celestial sphere marked by arbitrary boundary lines. [14]
3074	Co-Range Line	A line through points of equal tide range. [14]
3075	Corer: Piston	A corer equipped with a piston inside the core tube that is connected to the lowering cable. When the corer penetrates the ocean bottom the stopped cable and piston, in effect, provides a suction which overcomes the frictional forces acting between the sediment and the interior wall of the coring tube. [14]
3076	Cotidal Chart	See chart. [14]
3077	Crystal Clock	See clock. [14]
3078	Cumulus Stage	The initial stage in the development of an ordinary cell thunderstorm in which rising, warm, humid air develops into a cumulus cloud. [1]
3079	Current Chart	See chart. [14]
3080	Cut: Angle Of	See angle: crossing. [14]
3081	Day: Sidereal	The duration of one rotation of the earth on its axis, with respect to the vernal equinox over the upper branch of a meridian. Because of the precession of the equinoxes, the sidereal day thus defined is slightly less than the period of rotation with respect to the stars, but the difference is less than 0.01 second. The length of the sidereal day is 24 hours of sidereal time or 23h56m04.091s of mean solar time. [14]
3082	Deep Sea Lead	See lead. [14]
3083	Density Layer	A layer of water in which density increases with depth enough to increase the buoyancy of a submarine. [14]
3084	Digital Chart	See electronic chart. [14]
3085	Discriminator	A radar circuit that produces a response which depends upon the frequency of the input signal. A transponder beacon circuit which accepts pulses of proper duration and rejects others. That part of a frequency modulation receiver which converts the modulated signals directly into audio frequency signals. [14]
3086	Dock: Graving	See dock: dry. [14]
3087	Dredging Buoy	A buoy marking the limit of an area where dredging is being performed. [14]
3088	Drift Station	A scientific station established on the ice of the arctic ocean. A term sometimes used in shoran operations to designate the ground station about which the aircraft flies. The second station is then referred to as rate station. [14]
3089	Dry Lightning	Lightning that occurs with thunderstorms that produce little, if any, appreciable precipitation that reaches the surface. [1]
3090	Due Publicity	Notification of a given action for general information through appropriate authorities within a reasonable amount of time in a suitable manner. Used in the context of the united nations' law of the sea convention. [14]
3091	Electrometeor	Visible or audible manifestation of atmospheric electricity, either corresponding to discontinuous electrical discharges (lightning, thunder) or occurring as more or less continuous phenomena (saint elmo's fire, polar aurora). [14]
3092	Envelope Edge	The fore part of an envelope. [14]
3093	Eotvos Effect	The east-west component of the movement of a ship, including the effect of marine currents, modifies the centrifugal force of the earth's rotation. It is a vertical force experienced by a body moving in an east-west direction on the rotating earth. [14]
3094	Equator: Heat	See equator: thermal. [14]
3095	Error: Random	See error: accidental. [14]
3096	Expert System	A knowledge-based computer system which utilizes artificial intelligence to do some of the inferential computation/decision making. [14]
3097	Exposure Time	The time during which a light-sensitive material is subjected to the action of light. [14]
3098	Extrapolation	The process of estimating the value of a quantity beyond the limits of known values by assuming that the rate or system of change between the last few known values continues. [14]
3099	Extreme Value	Design value of a parameter used in ultimate limit state checks, in which a structure's global behavior is intended to stay in the elastic range. NOTE Extreme events have probabilities of the order of 10^-2 per annum. [15]
3100	False Horizon	See horizon. [14]
3101	Fix: Circular	A useless fix resulting from the observations of two angles establishing as loci three coinciding circles of position. Also called revolver, or swinger. [14]
3102	Floating Dock	See dock. [14]
3103	Flux: Radiant	Power emitted, transferred or received in the form of radiation. [14]
3104	Following Sea	A sea in which the waves move in the general direction of the heading. [14]
3105	Fracture Zone	An extensive linear zone of irregular topography, mountainous or faulted, characterized by steep-sided or asymmetrical ridges, clefts, troughs, or escarpments. [14]
3106	Fringing Reef	A reef closely attached to a shore, as contrasted with a barrier reef which is separated from the shore by a lagoon. [14]
3107	Gaussin Error	See error. [14]
3108	General Chart	See chart. [14]
3109	Geodetic Data	Information concerning points established by a geodetic survey, such as descriptions for recovery, coordinate values, height above sea level, and orientation. [14]
3110	Geomorphology	A branch of both geography and geology that deals with the form of the earth, the general configuration of its surface, and the changes that take place in the evolution of land forms. [14]
3111	Grab Sampling	A random mode of collecting samples. [14]
3112	Gradient Wind	A theoretical wind that blows parallel to curved isobars or contours. [1]
3113	Graphic Scale	See scale: bar. [14]
3114	Gravity Meter	See gravimeter. [14]
3115	Harbour Chart	See chart. [14]
3116	Harbour Reach	The reach of a winding river or estuary which leads directly to the harbor. [14]
3117	Hazard Beacon	See beacon. [14]
3118	Height Finder	A stereoscopic range finder so constructed as to indicate vertical heights rather than slant range. [14]
3119	Horizon Shade	One of the pivoted coloured glasses which can be swung before the horizon glass of a sextant to regulate the intensity of light. [14]
3120	Horizon: True	In photogrammetry, a horizontal plane passing through a point of vision or perspective center. The apparent horizon approximates the true horizon only when the point of vision is very close to sea level. [14]
3121	Icelandic Low	The subpolar low-pressure area that is centered near iceland on charts that show mean sea-level pressure. [1]
3122	Indian Summer	An unseasonably warm spell with clear skies near the middle of autumn. Usually follows a substantial period of cool weather. [1]
3123	Indirect Wave	See wave. [14]
3124	Insular Shelf	A zone around an island that extends from the low water line to a depth at which there is usually a marked increase of slope towards oceanic depths. [14]
3125	Isoporic Line	A line connecting points of equal annual rate of change of a magnetic element. Also called isopor. [14]
3126	Kalman Filter	In electronics, a mathematical-statistical method for predicting a time-variable signal in the presence of disturbances. The method exploits the fact that certain characteristic parameters of the process vary slowly with time, so that a best estimate of the signal can be obtained as a function of time. [14]
3127	Landfall Buoy	See farewell buoy. [14]
3128	Layer Tinting	See layering. [14]
3129	Light: Linear	A luminous signal having perceptible length, as contrasted with a point light. [14]
3130	Light: Marine	A light intended primarily for marine navigation. [14]
3131	Line Of Force	A line indicating the direction in which a force acts, as in a magnetic field. See magnetic lines of force. [14]
3132	Line Of Nodes	The straight line connecting the two points of intersection of the orbit of a planet, planetoid, or comet and the ecliptic, or the line of intersection of the planes of the orbits of a satellite and its primary. See node. [14]
3133	Lithification	The process of induration, cementation, petrification, consolidation, and crystallization which convert magma and newly deposited sediments into rock. [14]
3134	Local Horizon	See horizon: apparent. [14]
3135	Local Transit	See transit. [14]
3136	Log: Electric	A graphic recording of the various electrical properties of a sediment or rock through which a hole has been drilled. [14]
3137	Log: Taffrail	A log consisting essentially of a rotator towed through the water by a braided log line attached to a distance registering device usually secured at the taffrail, the railing at the stern. Also called patent log. [14]
3138	Lunar Rainbow	See moonbow. [14]
3139	Make The Land	To sight and approach or reach land from seaward. [14]
3140	Map: Thematic	A map designed to demonstrate particular features or concepts. In conventional use, this term excludes topographic maps. [14]
3141	Marine Growth	Living organisms attached to an offshore structure. [15]
3142	Marsden Chart	A system introduced by marsden early in the nineteenth century for showing the distribution of meteorological data on a chart especially over the oceans. A Mercator map projection is used; the world between 90°n and 80°s being divided into marsden 'squares' each of 10 degrees latitude by 10 degrees longitude. These squares are systematically numbered to indicate position. Each square may be divided into quarter squares, or into 100 one-degree subsquares numbered from 00 to 99 to give the position to the nearest degree. [14]
3143	Measured Mile	A measured distance of one nautical mile. [14]
3144	Medimarimeter	An apparatus for recording the mean sea level. [14]
3145	Melting Point	Temperature of change from the solid to the liquid phase of a substance. It is a function of pressure. [14]
3146	Meteoric Dust	Atmospheric dust originating from meteors. [14]
3147	Middle Ground	A shallow area in otherwise deeper water with channels on both sides of it. [14]
3148	Mixed Current	See current. [14]
3149	Moirã© Effect	The effect created by transmitting light through two separate, overlapping families of parallel lines. See also inogen light. [14]
3150	Monochromatic	(Adj.). Of, or having one colour. Of, or producing light of one wavelength. [14]
3151	Nadir: Ground	The point on the ground vertically beneath the perspective center of the camera lens. [14]
3152	Natural Scale	See scale. [14]
3153	Nautical Plan	A large scale nautical chart or a large scale inset of a nautical chart. [14]
3154	Nitrogen (N2)	A colorless and odorless gas that occupies about 78 percent of dry air in the lower atmosphere. [1]
3155	Nominal Range	See range. [14]
3156	Oceanic Ridge	A long elevation of the ocean floor with either irregular or smooth topography and steep sides, often separating ocean basins. [14]
3157	Off Soundings	Said of a vessel navigating beyond the 100-fathom line. In earlier times, said of a vessel in water deeper than could be sounded with the hand lead. [14]
3158	Open Pack Ice	Floes seldom in contact with many leads and pools. Ice concentration 4/10th to 9/10th. [14]
3159	Open Traverse	See traverse. [14]
3160	Origin: False	See coordinates: false. [14]
3161	Oropesa Sweep	Towed wire used for sweeping sea bottom when surveying shoals or wrecks. It consists of a wire running from the stern of the vessel and held out on the water by an otter which also pulls down against a towed float. The amount of wire between float and otter determines the depth of the outer end of the sweep. The inner end of the sweep is held to the required depth and in line with the stern of the vessel by a kite. [14]
3162	Orthophotomap	A photomap made from an assembly of orthophotographs. It may incorporate special cartographic treatment, photographic edge enhancement, colour separation, or a combination of these. [14]
3163	Parantiselena	Photometeor of the halo family, analogous to the paranthelion, the luminary being the moon. [14]
3164	Pilot Station	The office or headquarters of pilots; the place where the services of a pilot may be obtained. [14]
3165	Polar Bearing	See bearing. [14]
3166	Port Handbook	A handbook for a specific port. [14]
3167	Primary Radar	See radar. [14]
3168	Print: Ozalid	A photographic contact print developed by a dry diazo process. The process produces a positive from a positive image or a negative from a negative image. [14]
3169	Quarter Point	The fourth of the distance from one point of the compass to another, equivalent to about two degrees and forty-nine minutes. [14]
3170	Radar Bearing	See bearing. [14]
3171	Radial: Nadir	A radial from the nadir point. See nadir: photograph. [14]
3172	Radiation Fog	A major type of fog, produced over a land area when radiational cooling reduces the air temperature to or below its dew point. [14]
3173	Radio Horizon	The line at which direct rays from a transmitting antenna become tangent to the earth's surface. Its distance from the transmitting antenna is greater than that of the visible horizon, and increases with decreasing frequency. [14]
3174	Radio Wave(S)	See wave. [14]
3175	Ratio Of Rise	The ratio of the height of tide at two places. [14]
3176	Relative Wind	For a moving object, wind vector relative to this object. Also called apparent wind. See true wind. [14]
3177	Repeatability	See repeatable accuracy. [14]
3178	Return Stroke	The luminous lightning stroke that propagates upward from the earth to the base of a cloud. [1]
3179	River Harbour	A harbor which lies on the banks of a river. [14]
3180	Rod: Sounding	See sounding pole. [14]
3181	Rodded Points	Points where the rod was actually held, as opposed to points sketched in between. [14]
3182	Roentgen Rays	See x-rays. [14]
3183	Sailing Chart	See under chart. [14]
3184	Sallying Ship	Producing rolling motion of a vessel by the running in unison of a group from side to side. This is usually done to help float a vessel which is aground or to assist it to make headway when it is beset by ice. [14]
3185	Scale: Border	A scale drawn along the border of chart. [14]
3186	Scale: Linear	See scale: bar. [14]
3187	Scintillation	Rapid variations, often in the form of pulsations, of the brightness of the stars or terrestrial light sources. [14]
3188	Sediment Core	See core. [14]
3189	Sediment Trap	A device used to measure the rate and amount of sedimentation in a location. [14]
3190	Sedimentation	The process of breakup and separation of particles from the parent rock, their transportation, deposition, and consolidation into another rock. [14]
3191	Sedimentology	The science concerned with the description, classification, origin, and interpretation of sediments and sedimentary rock. [14]
3192	Sensible Heat	The heat we can feel and measure with a thermometer. [1]
3193	Sextant Chart	See circle sheet. [14]
3194	Sextant Error	See error. [14]
3195	Sextant: Gyro	A sextant provided with a gyroscope to indicate the horizontal. [14]
3196	Siberian High	A strong, shallow area of high pressure that forms over siberia in winter. [1]
3197	Signal: Sound	See sound signal. [14]
3198	Signal: Water	A hydrographic signal erected in shallow water. [14]
3199	Sketch Survey	See survey. [14]
3200	Solitary Wave	See wave. [14]
3201	Sonic Bearing	See bearing. [14]
3202	Sounder: Echo	See echo sounder. [14]
3203	Sounding Pole	A graduated pole or rod used for sounding in shallow water. Also called sounding rod. [14]
3204	Sounding Tube	A glass tube of small diameter, used with certain types of sounding machines in determining depth. [14]
3205	Speed: Ground	See ground speed. [14]
3206	Speed: Linear	Rate of motion in a straight line. [14]
3207	Spirit Bubble	See level: spirit. [14]
3208	Storm Warning	See warning. [14]
3209	Straight-Edge	A bar of wood, metal, etc. With one edge accurately straight for drawing straight lines in cartographic applications. [14]
3210	Stratocumulus	A low cloud, predominantly stratiform, with low, lumpy, rounded masses, often with blue sky between them. [1]
3211	Stream: Flood	See flood stream. [14]
3212	Stream: Tidal	See current: tidal. [14]
3213	Sumner Method	The establishing of a line of position from the observation of the altitude of a celestial body by assuming two latitudes (or longitudes) and calculating the longitudes (or latitudes) through which the line of position passes. [14]
3214	Sun: Apparent	The actual sun as it appears in the sky. Also called true sun. [14]
3215	Sunspot Cycle	The time interval (11.2 years) during which the number of sunspots progresses from a minimum to a maximum and decreases again to a minimum. [14]
3216	Super Typhoon	A tropical cyclone (typhoon) in the western pacific that has sustained winds of 130 knots or greater. [1]
3217	Survey: Sonar	Hydrographic survey using a sonar. [14]
3218	Swallow Float	A tubular buoy, usually made of aluminium, that can be adjusted to remain at a selected density level to drift with the motion of that water mass. The float is tracked by shipboard listening devices and current velocities can be determined. [14]
3219	Swash Channel	A channel across a bank, or among shoals. [14]
3220	Tangent Screw	A slow motion screw of a surveying instrument or sextant. [14]
3221	Target: False	See echo: false. [14]
3222	Thermal Belts	Horizontal zones of vegetation found along hillsides that are primarily the result of vertical temperature variations. [1]
3223	Thermal Layer	See thermocline. [14]
3224	Tidal Harbour	See harbor. [14]
3225	Tide Register	See gauge: tide. [14]
3226	Tide(S): Neap	The tides of decreased range occurring near the times of first and last quarter. [14]
3227	Tide: Falling	The portion of the tide cycle between high water and the following low water. Also called ebb tide. The opposite is rising tide. [14]
3228	Tide: Oceanic	The periodic rise and fall of the earth's oceans resulting from gravitational interactions between the sun, moon, and earth. [14]
3229	Tide: Partial	One of the harmonic components comprising the tide at any point. The periods of the partial tides are derived from various combinations of the angular velocities of earth, sun, moon, and stars relative to each other. See harmonic constituent. [14]
3230	Tide: Primary	That part of a tidal undulation that is the direct response to a tide-producing force. [14]
3231	Tide: Weather	See tide: windward. [14]
3232	Topoangulator	An instrument used to measure vertical angles in the principal plane of an oblique photograph. [14]
3233	Tornado Alley	A region in the great plains of the united states extending from texas and oklahoma northward into kansas and nebraska where tornadoes are most frequent. [1]
3234	Tornado Watch	A forecast issued to alert the public that tornadoes may develop within a specified area. [1]
3235	Total Eclipse	See eclipse. [14]
3236	Tracing Paper	A thin tough semitransparent paper suitable for making tracings of drawings, or for miscellaneous use in hydrographic work, where permanence is not important or when pencil work is sufficient. [14]
3237	Track Plotter	A plotter used to plot the track or course of a craft. [14]
3238	Training Wall	A wall, bank, or jetty, often submerged, built to direct or confine the flow of a river or tidal current. [14]
3239	Translocation	A method to improve the accuracy of satellite positioning by simultaneously using several receivers. One receiver is deployed on a known position to obtain corrections required to match the known position and that derived from satellite signals. These corrections are then transmitted to the other receivers. [14]
3240	Trilateration	A method of surveying wherein the lengths of the triangle sides are measured, usually by electronic methods, and the angles are computed from the measured lengths. Compare with triangulation. [14]
3241	Tripod Signal	See signal. [14]
3242	True Meridian	See meridian. [14]
3243	Turning Basin	An enlargement of a channel for turning vessels. Also called manoeuvering basin. [14]
3244	Uplifted Reef	A coral reef exposed above water level. [14]
3245	Violent Storm	Wind with a speed between 56 and 63 knots (beaufort scale wind force 11). [14]
3246	Warning: Gale	Meteorological message intended to warn those concerned of the occurrence or expected occurrence of a wind of beaufort force 8 or 9 over a specified area. [14]
3247	Water Content	A ratio; 100 multiplied by the weight of water in a bottom sediment sample divided by the weight of the dried sample, expressed as a percentage. [14]
3248	Water Sampler	Any device for obtaining a water sample. Also called water sampling device. See water bottle. [14]
3249	Water-Parting	A summit or boundary line separating the drainage districts of two streams or coasts; a divide or watershed. [14]
3250	Wave Velocity	The speed at which the individual wave form advances. A vector quantity that specifies the speed and direction with which a sound wave travels through a medium. [14]
3251	Wave: Carrier	A radio wave used as a vehicle for conveying intelligence, generally by modulation. Also called carrier. [14]
3252	Wave: Gravity	A wave whose velocity of propagation is controlled primarily by gravity. Water waves of length greater than 2 inches are considered gravity waves. [14]
3253	Wave: Surface	A progressive gravity wave in which the disturbance (that is, the particle movement in the fluid mass as well as the surface movement) is confined to the upper limits of a body of water. Strictly speaking this term applies to those progressive gravity waves whose celerity depends only upon the wavelength. [14]
3254	Weather Shore	Shore that is to windward of a vessel. See lee shore. [14]
3255	Weather Types	Certain weather patterns categorized into similar groups. Used as an aid in weather prediction. [1]
3256	Weather Watch	A forecast indicating that atmospheric conditions are favorable for hazardous weather to occur over a particular region during a specified time period. [1]
3257	Weathered Ice	Hummocked polar ice subjected to weathering which has given the hummocks and pressure ridges a rounded form. If the weathering continues, the surface may become more and more even. [14]
3258	Weighted Mean	A value obtained by multiplying each of a series of values by its assigned weight and dividing the sum of those products by the sum of the weights. [14]
3259	Well: Plugged	A borehole which has been sealed with a plug and permanently abandoned. [14]
3260	Wind Machines	Fans placed in orchards for the purpose of mixing cold surface air with warmer air above. [1]
3261	Wind Profiler	A doppler radar capable of measuring the turbulent eddies that move with the wind. Because of this, it is able to provide a vertical picture of wind speed and wind direction. [1]
3262	Windward Tide	See tide. [14]
3263	Working Chart	See chart. [14]
3264	X-Coordinates	See coordinates: plane rectangular. [14]
3265	Y-Coordinates	See coordinates: plane rectangular. [14]
3266	Zenith Camera	A special camera so designed that its optical axis may be pointed accurately toward the zenith. It is used for the determination of astronomical positions by photographing the position of the stars. [14]
3267	Zone Meridian	The central meridian of each zone of a grid system. [14]
3268	Abnormal Value	Design value of a parameter of abnormal severity used in accidental limit state checks in which a structure is intended not to suffer complete loss of integrity [15]
3269	Absolute Error	See error. [14]
3270	Altitude: True	The apparent altitude of a celestial body after all corrections have been applied. In American terminology usually referred to as observed altitude. [14]
3271	Anaglyphic Map	See under map. [14]
3272	Anallatic Lens	A convergent lens fitted between the objective lens and the diaphragm of telescopes of instruments for direct measurements of distances between the optical center of the instrument and a graduated staff called stadia. [14]
3273	Area Clearance	The effective depth, within specified limits, obtained by a wire drag survey. [14]
3274	Ascending Node	See node. [14]
3275	Autocollimator	See collimator. [14]
3276	Axis Of Camera	A line perpendicular to the focal plane of the camera and passing through the emergent nodal point of the lens system. Also called camera axis. See nodal point. [14]
3277	Axis: Trunnion	See axis: horizontal. [14]
3278	Axis: Vertical	In a theodolite or transit, the line through the center of the instrument about which the alidade rotates. [14]
3279	Band Of Colour	See stripes (of colour) [14]
3280	Base Direction	See direction. [14]
3281	Base Terminals	The two extremes of a base line. Usually marked on a monument or metal stake buried beneath a visible surface mark. See also reference mark. [14]
3282	Beacon: Hazard	A beacon marking an obstruction or hazard. [14]
3283	Bearing Circle	A ring designed to fit snugly over a compass or compass repeater, and provided with vanes for observing bearings. A similar ring provided with means for observing azimuth of the sun is called an azimuth circle. [14]
3284	Bearing: Polar	In a system of polar or spherical coordinates, the angle formed by the intersection of the reference meridional plane and the meridional plane containing the point. [14]
3285	Bearing: Radar	A bearing obtained by radar. [14]
3286	Bearing: Radio	The angle between the apparent direction of a definite source of emission of electro-magnetic waves and a reference direction, as determined at a radio direction-finding station. [14]
3287	Bottom Current	The movement of water along the bottom of reservoirs or rivers. [2]
3288	Bottom Sampler	Any device for obtaining a bottom sample. See also corer, dredge, driver rod, grab and snapper. [14]
3289	Boundary Layer	The layer of fluid in the immediate vicinity of a bounding surface. It is the layer in which frictional forces are not negligible. [14]
3290	Bubble Sextant	See sextant. [14]
3291	Buoy: Cardinal	A buoy used to indicate that the best navigable water is to be found in one particular of the quadrants that are bounded by the four bearings nw, ne, se and sw taken from the position of the mark. [14]
3292	Buoyant Beacon	See articulated light. [14]
3293	Cable: Coaxial	A transmission cable consisting of two concentric conductors insulated from each other. [14]
3294	Camera: Aerial	A camera specially designed for use in aircraft. [14]
3295	Capillary Wave	See wave. [14]
3296	Careening Grid	A structure in the intertidal zone serving as a support for vessels at low stages of the tide to permit work on the exposed portion of the vessel's hull. Also called gridiron. [14]
3297	Chart: Cotidal	A chart showing cotidal lines. [14]
3298	Chart: Current	A chart on which current data are graphically depicted. [14]
3299	Chart: Fishery	A chart with additional details required for the exploitation of marine natural resources. [14]
3300	Chart: General	A nautical chart intended for offshore coastwise navigation. [14]
3301	Chart: Harbour	A nautical chart intended for navigation and anchorage in harbors and small waterways. [14]
3302	Chart: Sailing	A small scale nautical chart for offshore navigation. [14]
3303	Chart: Working	In hydrographic survey, a working document (chart or projection) by means of which a survey programme can be broadly planned. [14]
3304	Circular Level	See level: spirit. [14]
3305	Civil Twilight	See twilight. [14]
3306	Clamping Error	See error. [14]
3307	Clear Sweeping	A form of bar sweeping. A sweep, set at a predetermined depth, and passed over an area to ensure that no obstructions have been missed. [14]
3308	Clearing Marks	Selected marks, natural or otherwise, used to help vessels keep clear of dangers. [14]
3309	Clock: Crystal	A precision clock essentially consisting of a generator of constant frequency controlled by a resonator made of quartz crystal with suitable methods for producing continuous rotation to operate time-indicating and related mechanisms. Also called quartz clock. [14]
3310	Close Pack Ice	Pack ice composed of floes mostly in contact, such that navigation becomes difficult even for specially constructed vessels. Ice concentration 7/10th to 9/10th. [14]
3311	Coastal Survey	See survey. [14]
3312	Cocurrent Line	A line through places having the same tidal current hour. [14]
3313	Compass Course	See course. [14]
3314	Compass Points	The 32 divisions of a compass, at intervals of 11°1/4. [14]
3315	Compass: Astro	An instrument which, when oriented to the horizontal and to the celestial sphere, indicates a horizontal reference direction relative to the earth. This compass is designed primarily for the observation of celestial bodies to determine the orientation of an aircraft relative to the azimuth of a celestial body. [14]
3316	Composite Path	A wave track which lies partly over land and partly over water. [14]
3317	Constant Error	See error. [14]
3318	Contour: Depth	See depth curve. [14]
3319	Control: Basic	See control. [14]
3320	Control: Minor	See control: photogrammetric. [14]
3321	Correspondence	In stereoscopy, the condition that exists when corresponding images on a pair of photographs lie in the same epipolar plane; the absence of y-parallax. [14]
3322	Co-Tidal Chart	A chart of a major harmonic constituent (or of a semi-diurnal tide) constructed to illustrate the propagation patterns and to assist in the interpolation of tidal conditions and datum assessment at locations where no observations exist (especially offshore). Now frequently replaced by numerical modelling. [16]
3323	Country Breeze	A light breeze that blows into a city from the surrounding countryside. It is best observed on clear nights when the urban heat island is most pronounced. [1]
3324	Cross Bearings	Two or more bearings used as intersecting lines of position for fixing the position of a craft. [14]
3325	Crossing Angle	See angle. [14]
3326	Current: Drift	A wide, slow-moving ocean current principally caused by winds. [14]
3327	Current: Earth	See current(s): telluric. [14]
3328	Current: Flood	See flood stream. [14]
3329	Current: Mixed	The type of tidal current characterized by a conspicuous difference in speed and duration between the two flood currents or two ebb currents occurring each tidal day. [14]
3330	Current: Surge	The coastal current influenced by remote waves. [14]
3331	Current: Tidal	The alternating horizontal movement of water associated with the rise and fall of the tide caused by tide-producing forces. Also called tidal stream. [14]
3332	Cycloidal Wave	See wave. [14]
3333	Damped Wave(S)	See wave. [14]
3334	Danger Bearing	See bearing. [14]
3335	Dangerous Rock	A sunken rock of a small area (pinnacle), at such a depth as to be considered dangerous to surface navigation. [14]
3336	Data Retrieval	The extraction of data which meet certain criteria from a file or data bank. [14]
3337	Data Telemetry	Measuring a quantity, and transmitting the measured value to a distant station where further processing takes place. [14]
3338	Depressed Pole	See pole. [14]
3339	Depth: Charted	The vertical distance from the chart datum to the bottom. [14]
3340	Dike (Or Dyke)	An artificial ditch to hold, or control the flow of water. An artificial embankment to contain or hold back water. In geology, a tabular body of igneous rock molded from molten rock within a fissure. [14]
3341	Dioptric Light	See light. [14]
3342	Dock: Floating	A form of dry dock consisting of a floating structure of one or more sections which can be partly submerged by controlled flooding to receive a vessel, then raised by pumping out the water so that the vessel's bottom can be exposed. [14]
3343	Dolphin Beacon	A minor light structure consisting of a number of piles driven into the bottom in a geometric or random pattern and drawn together, with a light mounted at the top. [14]
3344	Doppler Effect	The apparent change in wavelength, and therefore in frequency of radiant energy, when the distance between the source and the observer or receiver is changing. This effect is exploited in underwater acoustics and satellite positioning. [14]
3345	Drift Ice Foot	See ramp. [14]
3346	Drift Sounding	See sounding. [14]
3347	Dumping Ground	A sea area where dredged material or other potentially more harmful material e.g. Explosives, chemical waste, is deliberately deposited. See also spoil ground. [14]
3348	Dutchman'S Log	See log. [14]
3349	Earth Inductor	An electric instrument used to measure the inclination of the earth's magnetic field. [14]
3350	Earth'S Mantle	The relatively plastic region between the crust and core of the earth. Also called asthenosphere. [14]
3351	Echo(Es): Side	See echo(es): false. [14]
3352	Eclipse: Lunar	An eclipse of the moon. When the moon enters the shadow of the earth, it appears eclipsed to an observer on the earth. [14]
3353	Eclipse: Solar	An eclipse of the sun. When the moon passes between the sun and the earth, the sun appears eclipsed to an observer in the moon's shadow. [14]
3354	Eclipse: Total	An eclipse in which the entire source of light is obscured. [14]
3355	Eotvos Balance	See torsion balance. [14]
3356	Epipolar Plane	Any plane which contains the epipoles; therefore any plane containing the air base. Also called basal plane. [14]
3357	Equiphase Zone	See zone. [14]
3358	Error: Closing	See error of closure. [14]
3359	Error: Gaussin	Deviation of a magnetic compass due to transient magnetism which remains in a vessel's structure for short periods after the inducing force has been removed. This error usually appears after a vessel has been on the same heading for a considerable time. [14]
3360	Error: Heeling	The change in the deviation of a magnetic compass when a craft heels, due to the change in the position of the magnetic influences of the craft relative to the earth's magnetic field and to the compass. [14]
3361	Error: Regular	See error: systematic. [14]
3362	Error: Sextant	The error in the reading of a sextant, due either to lack of proper adjustment or to imperfection of manufacture. [14]
3363	Error: Station	See deflection of the vertical. [14]
3364	European Datum	Constituted by the international spheroid located at the potsdam origin. [14]
3365	Field Position	See position. [14]
3366	Fish Trap Buoy	A buoy marking the limits of a fish trap area. [14]
3367	Flux: Luminous	Quantity, characteristic of radiant flux which expresses its capacity to produce a luminous sensation. [14]
3368	Focal Distance	See focal length. [14]
3369	Fog: Advection	Fog which forms in the lower part of a moist air mass which moves over a colder surface. [14]
3370	Following Wind	Wind blowing in the general direction of a vessel's course. [14]
3371	Free Gyroscope	See gyro: free. [14]
3372	Generalisation	The omission of less important detail when compiling a chart. Its purpose is to avoid overloading charts where space is limited. [14]
3373	Geoengineering	The use of global scale technology fixes to mitigate climate changes. [1]
3374	Glacier Tongue	Projecting seaward extension of glacier, usually afloat. [14]
3375	Global Climate	Climate of the entire globe. [1]
3376	Gnomonic Chart	See chart. [14]
3377	Gravity Coring	A method to obtain cores by bottom penetration solely as a result of gravity. [14]
3378	Grid Direction	See direction. [14]
3379	Grid Variation	See variation. [14]
3380	Ground Effects	Influence exerted by the ground on the propagation of electromagnetic waves. [14]
3381	Group Velocity	The velocity of a wave disturbance as a whole, i.e., of an entire group of component simple harmonic waves. [14]
3382	Harbour Master	A local official who has charge of mooring and berthing of vessels, collecting harbor fees, etc. [14]
3383	Harbour: Inner	The part of a harbor more remote from the sea, as contrasted with the outer harbor. These expressions are usually used only in a harbor that is clearly divided into two parts, as by a narrow passageway or man-made structures. The inner harbor generally has additional protection and is often the principal berthing area. [14]
3384	Harbour: Outer	The part of a harbor towards the sea, through which a vessel enters the inner harbor. [14]
3385	Harbour: Tidal	A harbor affected by the tides, in distinction from a harbor in which the water level is maintained by caissons or gates. [14]
3386	Heat Lightning	Distant lightning that illuminates the sky but is too far away for its thunder to be heard. [1]
3387	Heat Lightning	Lightning flash at a distance which may be observed as a short illumination of the sky or of a cloud, close to the horizon. [14]
3388	Horizon Mirror	The mirror part of the horizon glass. The expression is sometimes used somewhat loosely to refer to the horizon glass. [14]
3389	Horizon: False	A line resembling the apparent horizon but above or below it. [14]
3390	Horizon: Radio	See radio. [14]
3391	Image: Virtual	An image that cannot be shown on a surface but is visible, as in a mirror. [14]
3392	Ingoing Stream	See flood stream. [14]
3393	Intended Track	See track. [14]
3394	Intervalometer	A timing device for automatically operating the shutter of a camera at selected intervals. [14]
3395	Inverted Image	See image. [14]
3396	Island Harbour	See under harbor. [14]
3397	Isopycnic Line	A line connecting points of equal density. Also called isopycnic. [14]
3398	Katabatic Wind	An offshore wind produced by cold air draining from high ground by convection. The cold air replaces the lighter warm air which is rising over the sea. [14]
3399	Kinetic Energy	The energy within a body that is a result of its motion. [1]
3400	Lateral System	A buoyage system generally used for well defined channels; buoyage marks indicate the position of dangers in relation to the route to be followed by mariners in their vicinity. [14]
3401	Latitude Scale	See scale. [14]
3402	Lead: Deep Sea	A heavy sounding lead the weight of which may be varied from about 15 to over 50 kilos depending on the depths to be sounded. Also called dipsey lead. [14]
3403	Lead: Sounding	A lead attached to a line used for measuring the depth of water. Also called plummet. [14]
3404	Level: Tilting	See levelling instrument: tilting level. [14]
3405	Line Of Levels	A continuous series of measured differences of elevation. [14]
3406	Liquid Compass	See compass. [14]
3407	Little Ice Age	The period from about 1550 to 1850 when average temperatures over Europe were lower, and alpine glaciers increased in size and advanced down mountain canyons. [1]
3408	Louver Shutter	See shutter. [14]
3409	Low Water Mark	The intersection of the plane of low water with the shore. The line along a coast, or beach, to which the sea recedes at low water. Also called low water line. [14]
3410	Lunar Distance	The angle, at an observer on the earth, between the moon and another celestial body. This was the basis of a method formerly used to determine longitude at sea. [14]
3411	Magnetic Chart	See chart. [14]
3412	Magnetic Range	See range. [14]
3413	Magnetic Storm	A disturbance in the earth's magnetic field, associated with abnormal solar activity, and capable of seriously affecting both radio and wire transmission. [14]
3414	Manuscript Map	See map. [14]
3415	Map: Cadastral	A map showing the boundaries of subdivision of land, usually with the bearings and lengths thereof and the area of individual tracts, for purposes of describing and recording ownership. A cadastral map may also show culture, drainage, and other features relating to the value and use of land. See also plat. [14]
3416	Marine Biology	See biology. [14]
3417	Marine Climate	A climate controlled largely by the ocean. The ocean's influence keeps winters relatively mild and summers cool. [1]
3418	Marine Railway	A track, cradle, and winding mechanism for hauling vessels out of the water so that the hull can be exposed as in a dry dock. This is also called a patent slip in British terminology. [14]
3419	Mark: Geodetic	See mark. [14]
3420	Master Station	The governing station of two or more synchronized transmitting stations. Often shortened to master. See slave station. [14]
3421	Matthews Table	An echo sounding correction table. [14]
3422	Mean Neap Rise	The height of mean high waters neaps above the chart datum. Also called neap rise. [14]
3423	Meridian Angle	Angular distance east or west of the local celestial meridian; the arc of the celestial equator, or the angle at the celestial pole, between the upper branch of the local celestial meridian and the hour circle of a celestial body, measured eastward or westward from the local celestial meridian through 180°, and labelled e or w to indicate the direction of measurement. See hour angle. [14]
3424	Meridian: Grid	One of the grid lines extending in a grid north-south direction. [14]
3425	Meridian: True	A meridian. The expression is used to distinguish the great circle through the geographical poles from magnetic meridian, compass meridian, or grid meridian. [14]
3426	Meridian: Zone	The meridian used for reckoning zone time. [14]
3427	Microprocessor	Component of a data processing device made up of microcircuits integrated on a single chip. [14]
3428	Mobile Station	A radiolocation station intended to be used at unspecified points. As opposed to fixed station. [14]
3429	Mountain Chain	A complexity of several mountain ranges. [14]
3430	Noon: Apparent	Twelve o'clock apparent time. [14]
3431	North: Compass	The direction north as indicated by a magnetic compass. [14]
3432	Notch (Or Gap)	A narrow passage between two elevations, as mountains; a deep close pass; a defile. [14]
3433	Open Roadstead	A roadstead with relatively little protection from the sea. [14]
3434	Optical Square	A small hand instrument used to set off a right angle. [14]
3435	Original Chart	See chart. [14]
3436	Orthochromatic	(Adj.). Said of photographic surfaces sensitive to ultra-violet, blue, yellow, green and orange rays. Insensitive to red rays. [14]
3437	Paleomagnetism	Remanent magnetism produced by the earth's field when a material was initially formed. [14]
3438	Parallel Plate	An optical disk with optically flat, parallel surfaces; used especially in optical micrometers. [14]
3439	Passive System	A system which records energy emitted or reflected but does not produce or transmit energy of its own. [14]
3440	Perigean Tides	See tide. [14]
3441	Periodic Error	See error. [14]
3442	Phase Velocity	Velocity, measured over a short time period, at which a particular wave crest is propagated a medium. [14]
3443	Photoengraving	A process by which photographs are reproduced on printing plates especially one in which the reproduction is in relief: opposed to photogravure. A plate so made. A print from such a plate. [14]
3444	Planning Chart	A chart designed for use in planning voyages or flight operations or investigating areas of marine or aviation activities. [14]
3445	Plotting Board	A stiff transparent polar coordinate plotting sheet for tracking other vessels and aircraft and solving problems involving relative movement. [14]
3446	Pocket Compass	See compass. [14]
3447	Poincarã© Wave	A long period gravity wave. The superposition of incident and reflected plane waves (Sverdrup waves) such that the composite wave fronts are perpendicular to the coast with a set of nodal lines normal to the wave fronts. The term is used in tidal analysis to study ocean tides and tides in open seas and gulfs. [14]
3448	Point Of Aries	See equinox. [14]
3449	Pole: Elevated	The celestial pole above the horizon, agreeing in name with the latitude. [14]
3450	Pole: Magnetic	See magnetic pole. [14]
3451	Port Authority	The entity responsible for administration and maintenance of harbor facilities. [14]
3452	Pressure Gauge	See gauge. [14]
3453	Pressure Plate	In photography, a flat plate (usually of metal but frequently of glass or other substance) which, by means of mechanical force, presses film into contact with the focal-plane plate of a camera. [14]
3454	Pressure Ridge	A ridge or wall of hummocked ice where one floe has been pressed against another. [14]
3455	Primary Circle	See primary great circle. [14]
3456	Principal Axis	See axis of lens. [14]
3457	Print: Contact	A photographic print made from either a negative or a positive in contact with a sensitized material. [14]
3458	Proof Plotting	An advanced copy of a map or chart produced by a plotter to check the design and registration, and to detect and correct errors before final printing. [14]
3459	Quartering Sea	Waves moving in a direction approximately 45° from a vessel's heading, striking the vessel on the quarter. [14]
3460	Radargrammetry	The process of obtaining reliable measurements in bi- and three-dimensional image processing by means of radar. [14]
3461	Radio Receiver	Equipment for receiving radio signals and converting them into usable form. [14]
3462	Radio Sonobuoy	See sonobuoy. [14]
3463	Radio Spectrum	The range of electromagnetic radiations useful for communication by radio (approximately 10 kilohertz to 300,000 megahertz). [14]
3464	Raise The Land	(v.t.). To sight land by approaching to the point where it appears above the horizon. [14]
3465	Range Light(S)	See light. [14]
3466	Range: Nominal	The luminous range of a light in a homogenous atmosphere in which the meteorological visibility is 10 sea miles. [14]
3467	Reflected Wave	See wave. [14]
3468	Refracted Wave	See wave. [14]
3469	Rocket Station	A life saving station equipped with line-carrying rocket apparatus. [14]
3470	Rod: Levelling	See levelling rod. [14]
3471	Rollers: Blind	See blind rollers. [14]
3472	Rossby Wave(S)	Ignoring friction or depth changes; if a parcel of water with no initial relative vorticity (i.e. No rotation) is moved northward, as f (the Coriolis parameter) increases the parcel will gain negative relative vorticity and will circulate clockwise. The Coriolis force will be greater on the poleward side of the parcel than on the equatorward side and hence the parcel will be subjected to a net south-ward restoring force. This force will push the parcel south of the latitude of zero relative vorticity overshoots and the circulation becomes counterclockwise. Due to the Coriolis variation the parcel will now experience a northward restoring force. Thus the variation of f provides a restoring force (in the horizontal plane) allowing oscillation to occur just as the effect of gravity does (vertically) for surface or internal waves. In reality rossby waves are complicated by depth variations and frictional effects. [14]
3473	Rotary Current	See current. [14]
3474	Rotating Light	See light. [14]
3475	Rotating Prism	See dove prism. [14]
3476	Routeing Guide	A document designed to be used in conjunction with nautical charts and other nautical publications in areas where complex routing systems have been established by the IMO. [14]
3477	Running Survey	See survey. [14]
3478	Sailing: Plane	A sailing in which the earth or a small part of it is considered a plane. [14]
3479	Santa Ana Wind	A warm, dry wind that blows into southern california from the east off the elevated desert plateau. Its warmth is derived from compressional heating. [1]
3480	Scale: Graphic	See scale: bar. [14]
3481	Seabed Sampler	A device used to obtain samples of the sea floor. [14]
3482	Seamount Chain	Several seamounts in a line with bases separated by a relatively flat sea floor. [14]
3483	Seamount Group	Several closely spaced seamounts not in a line. [14]
3484	Seamount Range	Several seamounts having connected bases and aligned along a ridge or rise. [14]
3485	Shear Strength	The internal resistance of a body to shear stress. [14]
3486	Signal Station	A place on shore from which signals are made to ships at sea. [14]
3487	Signal: Survey	A natural or artificial object or structure whose horizontal and sometimes vertical position is obtained by surveying methods. Survey signals are given special designation according to the kind of survey in which they are determined, or which they may later serve. [14]
3488	Signal: Tripod	A three-legged triangulation signal. It is usually constructed in such a manner that an observer can set up his theodolite and make observations without moving any of the structure. [14]
3489	Solar Parallax	See parallax. [14]
3490	Sounding: Echo	See echo sounding. [14]
3491	Sounding: Wire	Sounding with a sounding machine. To obtain a vertical wire sounding the ship or boat must be stopped while the wire is running out. [14]
3492	Speed Of Sound	The speed of propagation of sound waves. [14]
3493	Spherical Buoy	See buoy. [14]
3494	Spherical Wave	See wave. [14]
3495	Spring Tide(S)	See tide. [14]
3496	Stepped Leader	An initial discharge of electrons that proceeds intermittently toward the ground in a series of steps in a cloud- to-ground lightning stroke. [1]
3497	Stratification	The state of a fluid that consists of two or more horizontal layers arranged according to their density. [14]
3498	Stream Current	See current. [14]
3499	Stream: Rotary	See current: rotary. [14]
3500	Striding Level	See level. [14]
3501	Sublunar Point	The geographical position of the moon. That point on the surface of the earth at which the moon is in the zenith at a specified time. See sub-point. [14]
3502	Submarine Bell	A bell whose signal is transmitted through water. [14]
3503	Submerged Rock	A rock covered at the chart sounding datum and considered to be potentially dangerous to navigation. [14]
3504	Subsolar Point	The geographical position of the sun; that point on the earth at which the sun is in the zenith at a specified time. [14]
3505	Substitute Map	See map. [14]
3506	Sugar Loaf Sea	Waves that rise into sugar loaf shapes, with little wind, possibly resulting from intersecting waves. [14]
3507	Survey Station	See station. [14]
3508	Survey: Aerial	A survey using aerial photographs as part of the surveying operation; also the taking of aerial photographs for surveying purposes. [14]
3509	Survey: Ground	A survey made by ground methods, as distinguished from an aerial survey. A ground survey may or may not include the use of photographs. [14]
3510	Survey: Sketch	A hydrographic survey made (due to lack of time or facilities) to a lower degree of accuracy and detail than the chosen scale would normally indicate. [14]
3511	Tagline Survey	See survey. [14]
3512	Tandem Control	In hydrographic survey, a system of obtaining two or more adjacent sounding lines run simultaneously and controlled by one ship, the other ships, or launches being merely referenced to it. [14]
3513	Tape Stretcher	A mechanical device which facilitates holding a tape at a prescribed tension and in a prescribed position. [14]
3514	Tape: Standard	See reference tape. [14]
3515	Telegraph Buoy	A buoy used to mark the position of a submarine telegraph cable. [14]
3516	Tidal Light(S)	See light. [14]
3517	Tidal Movement	The movement which includes both the vertical rise and fall of the tide, and the horizontal flow of the tidal currents. This movement is associated with the astronomical tide-producing fores of the moon and sun acting upon the rotating earth. [14]
3518	Tidal Theories	The different theories trying to describe the tidal phenomena. [14]
3519	Tide: Analysis	The mathematical processes by which the observed tide or tidal current are analyzed to obtain constituents and statistics. [14]
3520	Tide: Compound	A tide constituent with a speed equal to the sum or difference of the speeds of two or more basic constituents. Compound tides usually occur in shallow water regions. See shallow water constituent. [14]
3521	Tide: Windward	A tidal current setting to windward. Also called weather tide. [14]
3522	Tilt: Relative	The angular relationship between two overlapping vertical photographs with no reference to an established datum. [14]
3523	Time: Sidereal	Time measured by the apparent diurnal rotation of the (true) vernal equinox. It is counted from 0 hour, when the vernal equinox is on the meridian, through 24 hours. Naming the meridian of reference is essential to its complete identification. [14]
3524	Time: Standard	A variation of zone time adapted for use on or near land, with irregular but well-defined zone limits. [14]
3525	Tornadogenesis	The process by which a tornado forms. [1]
3526	Transit: Local	The apparent passage of a celestial body across the meridian of the observer. See also meridian transit. [14]
3527	Traverse Point	See turning point. [14]
3528	Traverse Table	A table giving relative values of various parts of plane right triangles, for use in solving such triangles, particularly in connection with various sailings. [14]
3529	Tribrach Plate	A demountable, three-armed plate which is attached to an instrument stand or survey tower and on which the bottoms of the footscrews of the instrument rest in milled grooves. [14]
3530	Trough Compass	See declinatoire. [14]
3531	Turbulent Flow	A flow characterized by turbulence. [14]
3532	Twilight Stars	Stars suitably placed for astronomical observation during morning or evening twilight. [14]
3533	Underwater Ice	See anchor ice. [14]
3534	Valley: Median	See median valley. [14]
3535	Vanishing Line	In photogrammetry, the straight line on a photograph upon which lie all the vanishing points of all systems of parallel lines parallel to one plane. [14]
3536	Visible Region	Radiation with a wavelength between 0.4 and 0.7 mm. See visible radiation. [1]
3537	Warning: Storm	Meteorological message intended to warn those concerned of the occurrence or expected occurrence of a wind of beaufort force 10 or 11 over a specified area. More generally, forecast of severe weather conditions. [14]
3538	Wave Direction	The direction from which waves are moving. [14]
3539	Wave Steepness	Characteristic of individual waves defined as wave height divided by wavelength [14]
3540	Wave(S): Radio	Electromagnetic waves of frequencies generally higher than those of audible sound waves but lower than those of heat and light waves. Also called hertzian waves. [14]
3541	Wave: Cellular	System of surface waves in which the oscillation of water is limited as by solid boundaries. The period is the same in adjacent cells. [14]
3542	Wave: Indirect	Any wave which arrives by an indirect path having undergone an abrupt change of direction by refraction or reflection. See wave: sky. [14]
3543	Wave: Internal	A wave that occurs within a fluid whose density changes with depth, either abruptly at a sharp surface of discontinuity (an interface) or gradually. Also called boundary wave. [14]
3544	Wave: Pressure	See pressure wave. [14]
3545	Wave: Solitary	A wave of translation consisting of a single crest rising above the undisturbed liquid level, without any accompanying trough, in contrast with a wave train. [14]
3546	Weather Signal	See signal. [14]
3547	Well: Deviated	A borehole drilled at an oblique angle to evaluate or remove oil or natural gas reserves not directly below the drilling structure. [14]
3548	Wire: Sounding	See sounding. [14]
3549	Year: Sidereal	The period of one apparent revolution of the earth around the sun, with respect to a fixed point, or a distant star devoid of proper motion, being 365 days, 6 hours, 9 minutes, and 9.5 seconds in 1900 and increasing at the rate of 0.0001 second annually. [14]
3550	Zodiacal Light	White or yellowish light which spreads out, in the night sky, more or less along the zodiac from the horizon on the side on which the sun is hidden. It is observed when the sky is sufficiently dark and the atmosphere sufficiently clear. [14]
3551	Achromatic Lens	A compound lens that has been partly corrected for chromatic aberration. Such a lens is customarily made to bring green and red-light rays to approximately the same point focus. Also called achromat. See aberration of light. [14]
3552	Adjacent Coasts	The coasts lying either side of the land boundary between two adjoining states. [14]
3553	Air Photography	See photography: aerial. [14]
3554	Aluminium Sheet	An aluminium-mounted paper sheet occasionally used for boat-sheets, smooth sheets, or plane table boards. [14]
3555	Angle: Crossing	The angle at which two lines of position intersect. Also called angle of cut. [14]
3556	Angle: Masthead	See masthead angle. [14]
3557	Annual Parallax	See parallax. [14]
3558	Annular Eclipse	See eclipse. [14]
3559	Apogean Tide(S)	See under tide. [14]
3560	Aurora Borealis	Aurora of the northern hemisphere. [14]
3561	Axis Of Channel	The center line of a channel. See also talweg. [14]
3562	Axis: Principal	See axis of lens. [14]
3563	Azimuth Diagram	A diagram for obtaining graphically rather than by computation the azimuths of observed celestial bodies. [14]
3564	Bathythermogram	The record of temperature versus depth made by a bathythermograph. Rarely used. [14]
3565	Bearing: Danger	The maximum or minimum bearing of a point for safe passage of an offlying danger. [14]
3566	Biology: Marine	The study of the life, history and ecology of marine and brackish water plants and animals. [14]
3567	Bioluminescence	The emission of light by living organisms. See also noctiluca. [14]
3568	Bissextile Year	See year: civil. [14]
3569	Border Of Chart	The neatline defining the limits of the area charted. [14]
3570	Bottom Friction	The force resulting from the interaction between the ocean bottom and water particle motion over it. [14]
3571	Bottom Friction	The friction generated by the bathymetry. [19]
3572	Bottom Profiler	An echo sounder for precision surveys of the sea bottom surface. [14]
3573	Bottom Sampling	The process of collecting bottom samples. [14]
3574	Bridge: Bascule	A counterpoise bridge rotated in a vertical plane about an axis at one or both ends. Also called balance bridge. [14]
3575	Buoy: Automatic	See automatic floating station. [14]
3576	Cardinal System	A buoyage system generally used to indicate dangers where the coast is flanked by numerous islands, rocks and shoals as well as to indicate dangers in the open sea. In this system the bearing (true) of the mark from the danger is indicated to the nearest cardinal point. A system of buoyage in which the aids are assigned shape, colour, and number distinction in accordance with location relative to the nearest obstruction. The cardinal points delineate the sectors for buoy location. [14]
3577	Catoptric Light	See light. [14]
3578	Celestial Globe	See star globe. [14]
3579	Chart Portfolio	A systematic grouping of nautical charts covering a specific geographical area. [14]
3580	Chart: Magnetic	A chart showing for an established epoch the values of such magnetic elements as variation, dip, horizontal and vertical intensity of the earth's magnetic field, and total magnetic intensity. [14]
3581	Chart: Mercator	A chart on the Mercator projection. This is the chart commonly used for marine navigation. On a Mercator chart, a rhumb line is a straight line. [14]
3582	Chart: Original	A chart which has been drawn up as a result of direct survey. [14]
3583	Closed Traverse	See traverse. [14]
3584	Coastal Current	See current. [14]
3585	Comparing Watch	See watch. [14]
3586	Compass: Master	A compass controlling one or several repeaters. [14]
3587	Compass: Pocket	A portable compass (employed in coastlining or reconnaissance survey). [14]
3588	Compass: Spirit	See compass: liquid. [14]
3589	Compass: Trough	See declinatoire. [14]
3590	Concluded Angle	See angle. [14]
3591	Constituent Day	See day. [14]
3592	Continuous Wave	See wave. [14]
3593	Control: Ground	Control established by ground surveys, as distinguished from control established by photogrammetric methods. [14]
3594	Coordinatograph	An instrument used to plot in terms of plane rectangular coordinates. It may be an integral part of a stereoscopic plotting instrument whereby the planimetric motions (x and y) of the floating mark are plotted directly. [14]
3595	Counter Current	A secondary current setting in a direction opposite to that of a main current. [14]
3596	Course: Compass	See course. [14]
3597	Current: Rotary	A tidal current that flows continually, with the direction of flow changing through 360° during a tidal cycle. Called rotary stream in British terminology. [14]
3598	Current: Stream	A narrow, deep, and fast-moving current as opposed to a relatively wide and weak drift current. [14]
3599	Danger Sounding	See sounding. [14]
3600	Dangerous Wreck	A wreck submerged at such a depth as to be considered dangerous to surface navigation. [14]
3601	Day: Mean Solar	See day: solar. [14]
3602	Deep-Sea Camera	See camera. [14]
3603	Depth: Standard	A depth below the sea surface at which water properties should be measured and reported, according to the proposal by the international association of physical oceanography in 1936. [14]
3604	Descending Node	See node. [14]
3605	Desertification	A general increase in the desert conditions of a region. [1]
3606	Deviation Table	A table of the deviation of a magnetic compass on various headings, magnetic or compass. [14]
3607	Dipping Compass	See dip circle. [14]
3608	Direction: Base	In photogrammetry, the direction of the vertical plane containing the air base which might be expressed as a bearing or an azimuth. [14]
3609	Direction: Grid	Horizontal direction expressed as angular distance from grid north. [14]
3610	Dracontic Month	See month: nodical. [14]
3611	Echo(Es): False	In echo sounding, echoes caused by a foreign matter such as kelp or fish, or by layers of water differentiated by sudden changes of temperature or salinity (or both). False echoes are occasionally recorded by echo sounders, and might be interpreted erroneously as the correct depth. Also called side echo(es) or false target. See phantom bottom. [14]
3612	Ekman Transport	Net surface water transport due to the ekman spiral. In the northern hemisphere the transport is 90° to the right of the surface wind direction. [1]
3613	Enamelled Plate	In cartography, enamelled working surface (normally white), on aluminium, zinc or other dimensionally stable medium. Used to prepare colour separation originals. [14]
3614	Energy: Radiant	Energy transmitted by radiation. [14]
3615	Entrance Window	The image of the field stop formed by all the lens elements on the object side of the field stop. [14]
3616	Equation Method	In tidal terminology, an elaborate non-harmonic method for the prediction of tides. [14]
3617	Equation: Error	The probability equation which expresses the laws of the occurrence of accidental errors. The error equation is the basis of the method of least squares, used in the adjustment of observations for determining the most probable value of a result from those observations. [14]
3618	Error: Absolute	Absolute deviation (the value taken without regard to sign) from the corresponding true value. [14]
3619	Error: Clamping	A systematic error in observations made with a repeating theodolite caused by strains set up by the clamping devices of the instrument. [14]
3620	Error: Constant	A systematic error which is the same in both magnitude and sign through a given series of observations. [14]
3621	Error: External	See error: theoretical. [14]
3622	Error: Periodic	An error whose amplitude and direction vary systematically with time. [14]
3623	Error: Personal	The result of the inability of an observer to perceive dimensional values exactly. Personal errors may be either random or systematic in behavior. See also personal equation. [14]
3624	Error: Probable	An error (or deviation from the mean) of such magnitude that the likelihood of its being exceeded in a set of observations is equal to the likelihood of its not being exceeded; its value is that of the standard error multiplied by 0.6745. The use of standard error is sometimes preferred in statistical studies. [14]
3625	Error: Residual	The difference between any value of a quantity in a series of observations, corrected for known systematic errors, and the value of the quantity obtained from the adjustment of that series. Sometimes termed as residual. [14]
3626	Facility (Port)	See harbor works. [14]
3627	Fixing Interval	The time or distance elapsed between two subsequent fixes. [14]
3628	Foot (Pl. Feet)	A unit of length equal to 12 inches, 1/6 of a fathom, or 30.480 centimeters. [14]
3629	Free Atmosphere	See atmosphere. [14]
3630	Free Convection	See convection. [14]
3631	Frontal Surface	See front. [14]
3632	Gate: Hydraulic	A form of valve used to regulate the flow of a liquid in a pipeline, river or dam. [14]
3633	Gauge: Pressure	An instrument for measuring pressure. A tide gauge operated by the change in pressure at the bottom of a body of water, due to the rise and fall of the tide. [14]
3634	General Notices	All information and instructions that hydrographic offices may wish to bring to the attention of mariners but the nature of which is such that they may not properly refer to any specific nautical document. [14]
3635	Grad (Or Grade)	A unit of angle measurement, equal to the angle at the center of a circle, subtended by one four-hundredth part of its circumference. [14]
3636	Grid Navigation	See navigation. [14]
3637	Ground Distance	The great-circle distance between two ground positions, as contrasted with slant distance. Also called ground range. [14]
3638	Ground Parallel	See parallel. [14]
3639	Gyroscope: Free	See gyro: free. [14]
3640	Hanging Compass	See compass. [14]
3641	Harbour: Island	A harbor formed, or mainly protected, by islands. [14]
3642	Heat Index (Hi)	An index that combines air temperature and relative humidity to determine an apparent temperature how hot it actually feels. [1]
3643	High Water Mark	The mark left by the tide at high water. The line or level reached, especially the highest line ever reached. Also called high water line. A permanent mark which indicates the maximum observed stage of tide. [14]
3644	Hydrophotometer	An instrument used to measure the extinction coefficient of transmission of light in water. It consists of a constant light source placed at a specific distance from a photocell. When placed in water, the electrical output of the photocell is proportional to the amount of light striking the cell which, in turn, depends upon the transparency of the water. The instrument is calibrated to read 100 percent light transmission in air. [14]
3645	Image: Inverted	An image that appears upside down in relation to the object. [14]
3646	Inner Neat Line	See neat line. [14]
3647	Input Impedance	The complex opposition to alternating current between the input terminals of any device. [14]
3648	Intertidal Zone	The zone generally considered to be between mean high water and mean low water levels. [14]
3649	Isodynamic Line	A line connecting points of equal magnetic intensity, either the total or any component. [14]
3650	Land Navigation	See navigation. [14]
3651	Latitude Factor	The change in latitude along a celestial line of position per 1' change in longitude. [14]
3652	Level: Circular	See level: spirit. [14]
3653	Level: Striding	A spirit level so mounted that it can be placed above and parallel with the horizontal axis of a surveying or astronomical instrument, and so supported that it can be used to measure the inclination of the horizontal axis to the plane of the horizon. Generally, its mounting has supports in the form of inverted eyes which rest directly upon the pivots on which the telescope of the instrument rotates. [14]
3654	Levelling Plate	A plate designed to support the levelling rod as an aid to accuracy in levelling. [14]
3655	Levelling Screw	One of the three screws of surveying and astronomic instruments used for levelling same. Also called footscrew. [14]
3656	Levelling Staff	See levelling rod. [14]
3657	Light(S): Range	Two or more lights in the same horizontal direction, particularly those lights so placed as navigational aids to mark any line of importance to vessels, as a channel. The one nearest the observer is the front light and the one farthest from the observer is the rear light. See light(s): leading. [14]
3658	Light(S): Tidal	Lights shown at the entrance of a harbor to indicate tide and tidal current conditions within the harbor. [14]
3659	Light: Dioptric	A light concentrated into a parallel beam by means of refracting lenses and prisms (as opposed to catoptric). [14]
3660	Light: Flashing	A rhythmic light in which the total duration of light in a period is clearly shorter than the total duration of darkness and all the appearances of light are of equal duration. [14]
3661	Light: Isophase	See light: equal-interval. [14]
3662	Line Of Apsides	The line connecting the two orbital points (called apsides) that are nearest and farthest from the center of attraction, as the perigee and the apogee in the case of an orbit about the earth, and the perihelion and the aphelion in the case of an orbit about the sun. [14]
3663	Log: Dutchman'S	A buoyant object thrown overboard to determine the speed of a vessel by timing its passage between two marks, of known distance apart, on the vessel. [14]
3664	Lookout Station	A distinctive structure or place on shore from which personnel keep watch upon events at sea or along the coast. [14]
3665	Low Water Stand	See stand of tide. [14]
3666	Magnetic Course	See course. [14]
3667	Magnetic Moment	The quantity obtained by multiplying the distance between two magnetic poles by the average strength of the poles. [14]
3668	Magnetic Survey	See survey. [14]
3669	Mammatus Clouds	Clouds that look like pouches hanging from the underside of a cloud. [1]
3670	Map: Anaglyphic	A map specially printed in two complementary colors in such a way that, when viewed through a twin eyepiece of the same colors, a three-dimensional impression of relief is seen. [14]
3671	Map: Manuscript	The original drawing of a map as compiled or constructed from various data, such as ground surveys, photographs, etc. [14]
3672	Map: Substitute	A hasty reproduction of wide-coverage aerial photographs, photomaps, or mosaics, or of provisional maps, or any document used in place of a map, when the precise requirements of a map cannot be met. [14]
3673	Marks And Deeps	The divisions used in marking a hand lead line. [14]
3674	Maunder Minimum	A period from about 1645 to 1715 when few, if any, sunspots were observed. [1]
3675	Mean Neap Range	See neap range. [14]
3676	Mean Tide Level	See half tide level. [14]
3677	Meridian: Local	The meridian through any particular place or observer, serving as the reference for local time, in contrast with Greenwich meridian. [14]
3678	Meridian: Prime	The meridian of longitude 0°, used as the origin for measurement of longitude. The meridian of Greenwich, England, is almost universally used for this purpose. [14]
3679	Meridional Flow	A type of atmospheric circulation pattern in which the north-south component of the wind is pronounced. [1]
3680	Micrometer Drum	A graduated drum by which the motion of a traveling wire in a microscope can be measured. [14]
3681	Minimum Squares	See least squares. [14]
3682	Month: Sidereal	The interval of time between two successive passages of the moon past as fixed star. The length of the sidereal month averages 27.321661 mean solar days. [14]
3683	Month: Tropical	The average period of revolution of the moon about the earth with respect to the vernal equinox. The length of the tropical month averages 27.321582 mean solar days. [14]
3684	Nacreous Clouds	Clouds of unknown composition that have a soft, pearly luster and that form at altitudes about 25 to 30 km above the earth's surface. They are also called mother-of-pearl clouds. [1]
3685	North: Magnetic	The direction indicated by the north seeking pole of a freely suspended magnetic needle influenced only by the earth's magnetic field. [14]
3686	Oceanic Plateau	A comparatively flat topped elevation of the sea-bed which rises steeply from the ocean floor on all sides, and is of considerable extent across the summit. [14]
3687	Operative Sheet	See field board. [14]
3688	Opposite Coasts	The geographical relationship of the coasts of two states facing each other. [14]
3689	Orchard Heaters	Oil heaters placed in orchards that generate heat and promote convective circulations to protect fruit trees from damaging low temperatures. Also called smudge pots. [1]
3690	Orthophotoscope	A photomechanical device, used in conjunction with a double-projection anaglyphic instrument, for producing orthophotographs. [14]
3691	Outgoing Stream	See ebb stream. [14]
3692	Overlay Tracing	A plotting on tracing cloth at the scale of the smooth sheet used in conjunction with the smooth sheet. See fair chart. [14]
3693	Parallax: Solar	The equatorial horizontal parallax of the sun. [14]
3694	Partial Eclipse	See eclipse. [14]
3695	Phosphorescence	The production of light without sensible heat. Emission of electromagnetic radiation by a substance as a result of previous absorption of radiation of shorter wavelength. In contrast to fluorescence, the emission may continue for a considerable time after cessation of the existing irradiation. [14]
3696	Photogoniometer	An instrument for measuring angles from the true perspective center to points on a photograph. [14]
3697	Photograph Axes	See fiducial axes. [14]
3698	Photolithograph	A lithograph produced by photolithography. See lithography. [14]
3699	Phototopography	The science of surveying in which the detail is plotted entirely from photographs taken at suitable ground stations. [14]
3700	Pilotage Waters	See pilot waters. [14]
3701	Plane: Vertical	Any plane passing through a point on the earth and containing the zenith and nadir of that point. In surveying, a plane at right angles to a horizontal plane and within which angles and distances are observed. [14]
3702	Planimetric Map	See map. [14]
3703	Platform Jacket	The section of a platform from base to deck level, on which deck modules are fitted. [14]
3704	Platform: Piled	A platform with a steel jacket fixed by piles to the seabed. [14]
3705	Pole: Depressed	The celestial pole below the horizon, of opposite name to the latitude. [14]
3706	Position Angles	The two sextant angles observed on a survey ship for determining its position. [14]
3707	Position: Field	A position computed while field work is in progress to determine the acceptability of the observa-tions or to provide a preliminary position for other purposes. [14]
3708	Preferred Datum	A geodetic datum selected as a base for consolidation of local independent datums within a geographical area. Also called major datum. [14]
3709	Pressure: Sound	The instantaneous pressure at a point in a medium in the presence of a sound wave, minus the static pressure at that point. [14]
3710	Prevailing Wind	The wind direction most frequently observed during a given period. [1]
3711	Principal Scale	See scale. [14]
3712	Printing Plates	Any one-piece printing surface of any size, strength, or surface preparation, bearing an image made manually, mechanically or photographically, specifically for the purpose of printing such an image onto some other material. [14]
3713	Prohibited Area	An area shown on charts within which navigation and/or anchoring is prohibited. In aviation terminology, a specified area within the land areas of a state or territorial waters adjacent thereto over which the flight of aircraft is prohibited. [14]
3714	Quality Control	All procedures which ensure that the product meets certain standards and specifications. [14]
3715	Quarantine Buoy	A buoy marking the location of a quarantine anchorage. [14]
3716	Radar Reflector	A device capable of or intended for reflecting radar signals. [14]
3717	Radar-Responder	See radar beacon. [14]
3718	Radio Frequency	See frequency. [14]
3719	Radiotheodolite	Electronic theodolite designed to give the direction in space of a radio transmitter carried by a free balloon. [14]
3720	Range: Cruising	see cruising radius. [14]
3721	Range: Magnetic	A range oriented in a given magnetic direction and used to assist in determination of the deviation of a magnetic compass. See deviation: magnetic. [14]
3722	Ratio Of Ranges	The ratio of the height of tide at the subordinate station to the height of tide at the reference station. [14]
3723	Resolving Power	A mathematical expression of definition in a radar or optical system, usually stated as the maximum number of lines per millimeter that can be seen as separate lines in the image. [14]
3724	Reverse Azimuth	See azimuth: back. [14]
3725	Revolving Light	See light: rotating. [14]
3726	Rho-Teta System	Positioning system measuring the distance (rho) and direction (teta) from an existing control station to a mobile or another point. [14]
3727	River Discharge	The rate of flow of water past a point in a stream, expressed as volume per unit time (usually cubic feet per second). [14]
3728	River Roadstead	A roadstead which lies in a river. [14]
3729	Roaring Forties	An expression often used to denote that belt in the oceans, between 40° and 50° south latitude, where strong westerly winds prevail. [14]
3730	Rocket Sounding	Determination of one or more upper-air meteorological elements by means of rocket-borne instruments. [14]
3731	Runway Light(S)	See light. [14]
3732	Safe Water Mark	in the IALA maritime buoyage system a navigation mark used to indicate that there is navigable water around its position with no known hazards nearby. [14]
3733	Scale: Latitude	The subdivided east and west borders of a Mercator chart into degrees and minutes. A variant of the bar scale, since a minute of latitude is very nearly equal to a nautical mile. [14]
3734	Secondary Radar	See radar: primary. [14]
3735	Sediment Survey	A survey to determine the nature and distribution of types of sea bottom sediments. [14]
3736	Separation Line	See separation zone. [14]
3737	Sextant: Bubble	A sextant with a bubble or spirit level to indicate the horizontal. [14]
3738	Sextant: Marine	A sextant designed primarily for marine navigation. [14]
3739	Shoaling Effect	The alteration of a wave proceeding from deep water to shallow water. [14]
3740	Shutter: Louver	A shutter consisting of a number of thin metal strips or louvers which operate like a venetian blind to make the exposure; usually located just in front of or just behind the lens. [14]
3741	Signal: Weather	A visual signal displayed to indicate a weather forecast. [14]
3742	Single Day Tide	See tide: diurnal. [14]
3743	Solar Radiation	Radiation emitted by the sun. [14]
3744	Sonic Frequency	See audio frequency. [14]
3745	Sono-Radio Buoy	See sonobuoy. [14]
3746	Sound Intensity	See intensity. [14]
3747	Sounding Bottle	A strong metal container fitted with non-return valves for taking water samples at great depths. See also water bottle. [14]
3748	Sounding Record	Bound record book in which all of the data taken on a hydrographic survey are entered, and become part of the permanent records of the survey. Also called sounding book. [14]
3749	Sounding: Drift	A method of finding the least depth in a shoal area by letting the boat drift along a series of closely spaced, previously run parallel sounding lines, while the leadsman sounds or 'feels' along the bottom. The operation is repeated until the shoal is found or the area is covered. [14]
3750	Speed Made Good	The actual velocity of the ship along a course measured in relation to the ocean bottom or to fixed objects ashore. [14]
3751	Speed: Relative	See relative motion. [14]
3752	St. Elmo'S Fire	A bright electric discharge that is projected from objects (usually pointed) when they are in a strong electric field, such as during a thunderstorm. [1]
3753	Stadia Constant	The constant which is multiplied by the stadia interval to obtain the length of a sight in meters. [14]
3754	Stadia Interval	The length of rod subtended between the top and the bottom cross wires in the levelling instrument as seen projected against the face of the levelling rod. [14]
3755	Standardization	The comparison of an instrument or device with a standard to determine the value of the instrument or device in terms of an adopted unit. See calibration. [14]
3756	Star Identifier	See star finder. [14]
3757	Station: 'Lost'	See station: unrecoverable. [14]
3758	Station: Survey	See station. [14]
3759	Stationary Wave	See wave: standing. [14]
3760	Stream: Ingoing	See flood stream. [14]
3761	Streamline Flow	See laminar flow. [14]
3762	Submarine Cable	An assembly of wires or fibres, or a wire rope or chain, which has been laid underwater or buried beneath the sea floor. [14]
3763	Submarine Ridge	An elongated elevation of the sea floor, with either irregular or relatively smooth topography and steep sides which constitutes a natural prolongation of land territory. [14]
3764	Subtense Method	A procedure by which distance measurements are obtained by use of a subtense bar. [14]
3765	Summer Solstice	Approximately June 21 in the northern hemisphere when the sun is highest in the sky and directly overhead at latitude 231d2°n, the tropic of cancer. [1]
3766	Summer Solstice	See solstice. [14]
3767	Supersaturation	A condition whereby the atmosphere contains more water vapor than is needed to produce saturation with respect to a flat surface of pure water or ice, and the relative humidity is greater than 100 percent. [1]
3768	Surface Current	See current. [14]
3769	Surface Current	The current at the sea surface, which is partly due to the effects of wind and waves. Empirically, it is found that the drift current at the surface is 2.5%–3.0% of the wind speed, and it decreases rapidly in the uppermost meter. [5]
3770	Surge: Negative	An occasion when the level of the sea is lower than the predicted level. It is caused by meteorological conditions. [14]
3771	Surge: Positive	An occasion when the level of the sea is higher than the predicted level. It is caused by meteorological conditions. [14]
3772	Surging Breaker	See breaker. [14]
3773	Survey Traverse	See traverse. [14]
3774	Survey: Coastal	Hydrographic survey of coastal area including coast lining. [14]
3775	Survey: Harbour	Hydrographic survey of a harbor area. [14]
3776	Survey: Running	A hydrographic survey in which the greater part of the work is done from the ship steaming along the coast. A line of sounding is run on the course made good and any additional information of a hydrographic nature which can be obtained whilst under way, is collected. [14]
3777	Survey: Tagline	A large scale survey made by employing a tagline. An accurate method sometimes adopted in river and harbor work. [14]
3778	Swath(E) System	Any of a number of systems which are capable of obtaining a strip or lane of elevations or soundings from a single survey platforms ™s track. In hydrography, systems that fall into this category are multi beam echo sounders (mbes), interferometric echo sounders and lidar. [14]
3779	Tape: Reference	See reference tape. [14]
3780	Teleconnections	A linkage between weather changes occurring in widely separated regions of the world. [1]
3781	Theodolite Axes	See axis: horizontal and axis: vertical. [14]
3782	Theodolite Drag	See drag (of theodolite). [14]
3783	Thermal Equator	See equator. [14]
3784	Threshold Speed	The minimum speed of current at which a particular current meter will measure at its rated reliabi-lity. [14]
3785	Tidal Amplitude	The average difference between water levels at high and low tide ; One-half of the difference in height between consecutive high water and low water; hence, half of the tidal range. [6][8]
3786	Tide(S): Spring	The tides of increased range occurring near the times of full moon and new moon. [14]
3787	Tide: Vanishing	The phenomenon occurring when a high and low water 'melt' together into a period of several hours with a nearly constant water level. The tide is in the diurnal category but is known as a 'vanishing tide'. [14]
3788	Time: Universal	See universal time (ut). [14]
3789	Tornado Warning	A warning issued when a tornado has actually been observed either visually or on a radar screen. It is also issued when the formation of tornadoes is imminent. [1]
3790	Torsion Balance	A device for measuring very small forces of attraction resulting from gravitation, magnetism, etc., and consisting of a bar suspended horizontally by an elastic filament, one end of the bar being subjected to the influence of the attracting force to a greater degree than the other end. The attracting force is balanced and its comparative strength measured by the torsional reaction of the filament. [14]
3791	Track: Intended	The anticipated path of a vessel relative to the earth. [14]
3792	Transit Bearing	See bearing. [14]
3793	Tripping Device	A device to pull equipment out of or to lower it into water. [14]
3794	Tubular Compass	See compass. [14]
3795	Ultrashort Wave	See wave. [14]
3796	Universal Level	See level: spirit. [14]
3797	Unsurveyed Area	An area where hydrographic survey data is non-existent. [14]
3798	Vanishing Point	In photogrammetry, the image in the plane of a photograph, of the point toward which a system of parallel lines in the object space converges. [14]
3799	Visible Horizon	See horizon: apparent. [14]
3800	Water Levelling	See levelling. [14]
3801	Wave Generation	The creation of waves by natural or mechanical means. In wave forecasting the growth of waves caused by a wind blowing over a water surface for a certain period of time. The area involved is called the generating area or fetch. [14]
3802	Wave(S): Damped	Wave(s) the amplitude of which becomes progressively smaller. [14]
3803	Wave: Capillary	A wave whose velocity of propagation is controlled primarily by the surface tension of the liquid in which the wave is travelling. Water waves of length less than one inch are considered to be capillary waves. [14]
3804	Wave: Cycloidal	A very steep, symmetrical wave whose crest forms an angle of 120 degrees. The wave form is that of a cycloid. A trochoidal wave of maximum steepness. [14]
3805	Wave: Reflected	A wave that has had its direction of motion changed by reflection. [14]
3806	Wave: Refracted	A wave that has had its direction of motion changed by refraction. [14]
3807	Wave: Spherical	A wave whose wave front surfaces are concentric spheres. Such waves propagate from a point source. [14]
3808	Weather Warning	A forecast indicating that hazardous weather is either imminent or actually occurring within the specified forecast area. [1]
3809	Well: Appraisal	A borehole drilled to evaluate an oil field or gas field. [14]
3810	Well: Suspended	A borehole that has been temporarily abandoned pending future development. An obstruction up to 5 meters high may remain on the sea-floor. [14]
3811	Yaw (Or Yawing)	The ship's oscillation about a vertical axis approximately through the center of gravity of the vessel. [14]
3812	Zonal Wind Flow	A wind that has a predominate west-to-east component. [1]
3813	Zone Of Silence	See blind zone. [14]
3814	Zone: Equiphase	That region in space within which the difference in phase of two radio signals is indistinguishable. [14]
3815	Accidental Error	See error. [14]
3816	Acoustic Bearing	See bearing: sonic. [14]
3817	Active Satellite	An artificial satellite which transmits an electromagnetic signal. A satellite with the capability to transmit, repeat, or retransmit electromagnetic information as contrasted with passive satellite. 2. As defined by the international telecommunication union (itu), an earth satellite carrying a station intended to transmit or retransmit radiocommunication signals. [14]
3818	Aeromarine Light	See light. [14]
3819	Altimeter: Radar	See altimeter: radio. [14]
3820	Altitude: Flight	The vertical distance above a given datum, usually mean sea level, or an aircraft in flight. [14]
3821	Angle: Concluded	In a triangulation, the third angle of a triangle, not measured, but computed from the other two angles. [14]
3822	Angle: Vectorial	See coordinates: plane polar and coordinates: polar. [14]
3823	Anomalistic Year	See year. [14]
3824	Anomaly: Gravity	See gravity anomaly, bouguer anomaly, free air anomaly, isostatic anomaly. [14]
3825	Antarctic Circle	The geographic parallel having a south latitude equal to the complement of the declination of the winter solstice (latitude = 66 deg 33' s approximately). [14]
3826	Atmosphere: Free	That part of the atmosphere above the friction layer, in which the air motion is affected to a negligible degree by surface friction. [14]
3827	Atmosphere: Icao	Standard atmosphere adopted by the international civil aviation organization (ICAO). Its main features are mean sea-level pressure of 1013.25 mb, and a temperature lapse rate of 6.5° c/km from surface to the tropopause situated at 11 km. [14]
3828	Atmospheric Drag	A major perturbation of close artificial satellite orbits by the resistance of the atmosphere. [14]
3829	Aurora Australis	Aurora of the southern hemisphere. [14]
3830	Autumnal Equinox	The equinox at which the sun approaches the southern hemisphere and passes directly over the equator. Occurs around September 23. [1]
3831	Axis: Horizontal	In a theodolite or transit, the axis about which the telescope of the instrument rotates when moved vertically. Also called trunnion axis, or transit axis. [14]
3832	Azimuth: Forward	See azimuth: geodetic. [14]
3833	Azimuth: Laplace	A geodetic azimuth derived from an astronomic azimuth by means of the Laplace equation. [14]
3834	Azimuth: Reverse	See azimuth: back. [14]
3835	Backrush Current	See current: backrush. [14]
3836	Ballistic Camera	See camera. [14]
3837	Baseline: Normal	The low-water line along the coast as marked on large-scale charts officially recognized by the coastal state. [14]
3838	Bathythermograph	A device for obtaining a record of temperature against depth in the ocean, from a ship underway. [14]
3839	Bay Closing Line	A line dividing the internal waters and territorial seas in a bay. [14]
3840	Bearing: Compass	See bearing. [14]
3841	Bearing: Transit	A bearing taken of two objects when in line. [14]
3842	Bifurcation Buoy	See buoy: bifurcation. [14]
3843	Block Correction	See chartlet. [14]
3844	Bottom Sediments	See sediments: bottom. [14]
3845	Bridge Clearance	See clearance. [14]
3846	Broad On The Bow	Bearing 045° relative (broad on the starboard bow) or 315° relative (broad on the port bow). If the bearings are approximate, the expression on the bow should be used. See also on the bow. [14]
3847	Bull'S Eye Level	See level: spirit. [14]
3848	Cable: Submarine	An insulated, waterproof wire or bundle of wires for carrying an electric current under water. [14]
3849	Cadastral Survey	See survey. [14]
3850	Calling-In Point	a designated position at which vessels are required to report to a traffic control center. Also called reporting point or radio reporting point. [14]
3851	Camera: Deep Sea	A camera system specially designed for obtaining photographs of the ocean bottom. [14]
3852	Camera: Tracking	See camera: ballistic. [14]
3853	Cathode-Ray Tube	A vacuum tube in which electrons emitted by a hot cathode are formed into a narrow beam, accelerated at high velocity and directed towards a specially prepared screen which fluoresces at the point where the electrons strike. [14]
3854	Chain Adjustment	A mathematical adjustment of a whole series of figures, for example, a chain of triangulation. [14]
3855	Chart Production	All processes in the design, compilation, draughting and reproduction of a chart. [14]
3856	Chart Projection	See projection. [14]
3857	Chronometer Rate	The amount gained or lost by a chronometer in a unit of time. It is usually expressed in seconds per 24 hours, and is sometimes called daily rate. [14]
3858	Circle: Vertical	A great circle on the celestial sphere passing through the zenith and nadir. Vertical circles are perpendicular to the horizon. In a surveying instrument, the graduated circle used for measuring vertical angles. [14]
3859	Collimator: Auto	A collimator provided with a means of illuminating its cross hairs so that, when a reflecting plane is placed normal to the emergent light beam, the reflected image of the cross hairs appears to be coincident with the cross hairs themselves. This device is used in calibrating optical and mechanical instruments. [14]
3860	Comb: Micrometer	See micrometer. [14]
3861	Compact Pack Ice	Pack ice in which the concentration is 10/10 (8/8) and no water is visible. [14]
3862	Compass: Dipping	See dip circle. [14]
3863	Compass: Tubular	A compass supplied for attachment to certain types of levels and theodolites. [14]
3864	Contour Interval	The difference in elevation between adjacent contours. [14]
3865	Contour Sweeping	A form of bar sweeping. A sweep, set at a predetermined depth, and passed over the bottom at right angles to the depth contours. When contact is made the position is recorded. [14]
3866	Convection: Free	In the atmosphere, convection caused by density differences within the air. [14]
3867	Convergence Zone	In oceanography, region of convergence. The region in the deep ocean where sound rays, refracted from the depths, arrive at the surface in successive intervals of 30 to 35 nautical miles. [14]
3868	Corer: Polyvinyl	See corer: hydroplastic. [14]
3869	Cosmic Radiation	Radiation, of very high energy and great penetrative power, which emanates from cosmic regions. [14]
3870	Course: Magnetic	See course. [14]
3871	Crepuscular Rays	Alternating light and dark bands of light that appear to fan out from the sun's position, usually at twilight. [1]
3872	Current: Coastal	A relatively uniform drift usually flowing parallel to the shore in the deeper water adjacent to the surf zone. [14]
3873	Current: Density	A gradient current caused by the horizontal gradient of water density. [14]
3874	Current: Diurnal	The type of tidal current having only one flood and one ebb period in a tidal day. [14]
3875	Current: Surface	A current that does not extend more than a few (2-3) meters below the surface. [14]
3876	Cycle Per Second	A unit of frequency more and more superseded by the hertz. [14]
3877	Cylindrical Buoy	See can buoy. [14]
3878	Datum: Levelling	See datum: vertical control. [14]
3879	Day: Constituent	The duration of one rotation of the earth on its axis, with respect to a fictitious star representing one of the periodic elements in the tidal forces. It approximates the length of a lunar or solar day. The expression is not applicable to a long-period constituent. [14]
3880	Deadbeat Compass	See compass. [14]
3881	Deep Water Route	A route in a designated area within defined limits which has been accurately surveyed for clearance of sea bottom and submerged obstacles to a minimum indicated depth of water. [14]
3882	Degaussing Cable	See cable. [14]
3883	Dendrochronology	The analysis of the annual growth rings of trees as a means of interpreting past climatic conditions. [1]
3884	Direct Levelling	See levelling. [14]
3885	Distortion: Lens	See distortion. [14]
3886	Double Low Water	See low water. [14]
3887	Drafted Original	A scribed or drafted chart or portion of a chart on stable base material, which may be processed for final reproduction. [14]
3888	Drifting Logship	A logship employed for the measurement of tidal streams and currents. It is allowed to drift freely while its positions are fixed, during the period of observation, by an accompanying boat, or from stations ashore. [14]
3889	Duration Of Tide	The time interval between low water and the following high water or between high water and the following low water. [14]
3890	Eagre (Or Eager)	See bore. [14]
3891	Eclipse: Annular	An eclipse in which a thin ring of the source of light appears around the obscuring body. Annular solar eclipses occur, but never annular lunar eclipses. [14]
3892	Eclipse: Partial	An eclipse in which only part of the source of light is obscured. [14]
3893	Electrostriction	Term applied to the creation of elastic tension and changes of shape and volume of an uncharged isolator by an electrical field. [14]
3894	Equation Of Time	The correction to be applied to 12 hours plus universal time to obtain the Greenwich hour angle of the sun, or more generally the correction to be applied to 12 hours plus local mean time to obtain the local hour angle of the sun. [14]
3895	Equation: Normal	One of a set of simultaneous equations derived from observation, condition or correlate equations. In a least-squares adjustment, values obtained from the solution of normal equations (either directly or through the correlate equations) are applied to the observation or condition equations to obtain the desired corrections. [14]
3896	Equator: Thermal	Line which circumscribes the earth and connects all points of highest mean annual temperature on each meridian. Also called heat equator. [14]
3897	Equatorial Calms	Zone of calm or light variable winds encountered, in certain regions, between the trade winds of the two hemispheres. [14]
3898	Equinoctial Year	See year: tropical. [14]
3899	Equivalent Scale	See scale. [14]
3900	Error: Irregular	See error: accidental. [14]
3901	Everest Spheroid	See reference spheroid. [14]
3902	Expansion Factor	In radiolocation, factor representing the degree to which the hyperbolae belonging to a given group of hyperbolic lines of position move apart as the distance from the base line increases. [14]
3903	Eye Of The Storm	See tropical cyclone. [14]
3904	Fahrenheit Scale	A temperature scale where 32 is assigned to the temperature where water freezes and 212 to the temperature at which water boils (at sea level). [1]
3905	Field Inspection	In photogrammetry, the process of comparing aerial photographs with conditions as they exist on the ground, and of obtaining information to supplement or clarify that not readily discernible on the photographs themselves. [14]
3906	Fiord (Or Fjord)	A long narrow arm of the sea, running up between high banks or cliffs, as on the coast of norway. Often has a relatively shallow sill across its entrance. [14]
3907	Fix: Three-Point	A fix obtained by simultaneously observing, with sextants, the two adjacent angles between three suitably disposed objects whose positions are known, and plotting the position by a station pointer. See also resection and three-point problem. [14]
3908	Flat-Bed Plotter	A plotter which uses a flat surface to mount the drawing base. [14]
3909	Fractional Scale	See scale: natural. [14]
3910	Free-Air Anomaly	The difference between observed gravity and theoretical gravity which has been computed for latitude and corrected for elevation of the station above or below the geoid, by application of the normal rate of change of gravity for change of elevation, as in free air. Also called faye anomaly. [14]
3911	Geostrophic Wind	That horizontal wind velocity for which the coriolis force exactly balances the horizontal pressure force. [14]
3912	Grid Declination	The angular difference in direction between grid north and true north. It is measured east or west from true north. [14]
3913	Hanging Traverse	See traverse: open. [14]
3914	Helmert Spheroid	See reference spheroid. [14]
3915	High Water (H.W)	The highest level reached at a place by the water surface in one oscillation. Also called high tide. [14]
3916	High Water Stand	See stand of tide. [14]
3917	Highland Climate	The climate of high elevations. Also called mountain climate. There is no single climatic type but a variety of different climate zones often characterized by a rapid change in temperature and precipitation as one ascends or descends in elevation. [1]
3918	Hydrologic Cycle	A model that illustrates the movement and exchange of water among the earth, atmosphere, and oceans. [1]
3919	Hydrologic Front	A relatively narrow transition zone separating two water masses in the ocean. [14]
3920	Index Correction	That correction due to index error. [14]
3921	Innocent Passage	Navigation through certain sea areas of a coastal state without being prejudicial to the peace, good order or security of that state. See also transit passage. [14]
3922	Intensity: Sound	At a point, the average rate of sound energy transmitted in a specified direction through a unit area normal to this direction at the point considered. The square of the sound pressure. [14]
3923	Inverted Compass	See compass: hanging. [14]
3924	Ionospheric Wave	See wave: sky. [14]
3925	Isomagnetic Line	A line connecting points of equality in some magnetic element. [14]
3926	Laplace Equation	See equation. [14]
3927	Large Correction	(British terminology). A new printing of a chart corrected from important information which is too comprehensive to promulgate by admiralty notices to mariners or to insert conveniently by hand on existing copies of the chart. When large corrections are made, the chart is not revised throughout but all copies in circulation are cancelled. [14]
3928	Leading Light(S)	See light. [14]
3929	Lenticular Cloud	A cloud in the shape of a lens. [1]
3930	Level: Universal	See level: spirit. [14]
3931	Levelling: Water	A method of obtaining relative elevations by observing heights with respect to the surface of a body of still water, such as a lake. The relative elevations of objects along its shores are obtained by taking the differences of their heights with respect to the surface of the water. [14]
3932	Light(S): Runway	Lights marking a runway. [14]
3933	Light: Catoptric	A light concentrated into a narrow beam by means of one or more reflectors (as opposed to dioptric). [14]
3934	Light: Occulting	A rhythmic light in which the total duration of light in a period is clearly longer than the total duration of darkness and all the eclipses are of equal duration. [14]
3935	Light: Revolving	See light: rotating. [14]
3936	Light: Unwatched	A navigational light, usually automatic in operation, without any permanently stationed personnel to superintend it. [14]
3937	Litre (Or Liter)	The basic unit of capacity in the metric system. It is equal to one cubic decimetre. [14]
3938	Local Hour Angle	See hour angle. [14]
3939	Log Factor Scale	See scale. [14]
3940	Longitude Factor	The change in longitude along a celestial line of position per 1' change in latitude. [14]
3941	Longitude Signal	See signal. [14]
3942	Low Water (L.W.)	The lowest level reached at a place by the water surface in one oscillation. Also called low tide. [14]
3943	Lowest Low Water	An arbitrary level conforming to the lowest tide observed at a place, or somewhat lower. [14]
3944	Loxodromic Curve	A loxodrome. A rhumb line. [14]
3945	Lunar Inequality	Variation in the moon's motion in its orbit, due to attraction by other bodies of the solar system. See evection, perturbation. A minute fluctuation of a magnetic needle from its mean position, caused by the moon. [14]
3946	Magnetic Azimuth	See azimuth. [14]
3947	Magnetic Equator	See equator. [14]
3948	Magnetic Station	See station. [14]
3949	Magnifying Glass	A lens or combination of lenses that increases the apparent size of an object seen through it. [14]
3950	Magnifying Power	The ratio of the apparent length of a linear dimension as seen through an optical instrument to that seen by the unaided eye. Sometimes shortened to power. [14]
3951	Maintained Depth	The depth at which a channel is kept by human influence, usually by dredging. [14]
3952	Map: Planimetric	A map which presents only the horizontal positions for the features represented; distinguished from a topographic map by the omission of relief in measurable form. [14]
3953	Map: Topographic	A map which represents the horizontal and vertical positions of the features represented; distinguished from a planimetric map by the addition of relief in measurable form. A topographic map uses contours or comparable symbols to show mountains, valleys and plains. [14]
3954	Marine Barometer	See barometer. [14]
3955	Mean Spring Rise	The height of mean high water springs above the chart datum. Also called spring rise. [14]
3956	Mercator Sailing	See sailing. [14]
3957	Meridian Sailing	See sailing. [14]
3958	Meridional Plane	Any plane containing the polar axis of the earth. [14]
3959	Metre (Or Meter)	The basic unit of length in the si system. [14]
3960	Mid-Channel Buoy	A buoy for marking the middle of a channel. [14]
3961	Middle Latitudes	The region of the world typically described as being between 30° and 50° latitude. [1]
3962	Mid-Extreme Tide	See tide. [14]
3963	Mirage: Inferior	Particular case of mirage, occurring over stretches of water, land, shores, roads, etc. Strongly heated by insolation, and in which the virtual image is found below the actual object. The case in which objects situated on or slightly above the normal horizon become invisible is popularly termed sinking. [14]
3964	Mirage: Superior	Special case of mirage, observable over snow-fields, cold seas, etc., in which the virtual image is above the actual object. The case in which objects below and beyond the normal horizon become visible is popularly termed looming. [14]
3965	Month: Dracontic	See month: nodical. [14]
3966	Month: Synodical	The interval of time between two successive conjunctions or oppositions of the moon. The length of the synodical month is 29.5305888 mean solar days. Also called lunation or lunar month. [14]
3967	Morse Code Light	See light. [14]
3968	Navigable Waters	Waters usable, with or without improvements, as routes for commerce in the customary means of travel on water. [14]
3969	Navigation: Grid	Navigation by the use of grid directions. [14]
3970	Nontidal Current	See current. [14]
3971	Obstruction Buoy	A buoy marking an obstruction. [14]
3972	Occasional Light	See light. [14]
3973	Operating System	System which controls and monitors the execution of programs in the computer. [14]
3974	Orthophotomosaic	An assembly of orthophotographs forming a uniform-scale mosaic. [14]
3975	Outfall Diffuser	A structure on an outfall through which liquids are discharged. The structure will usually project above the level of the outfall and can be an obstruction to navigation. [14]
3976	Outflow Boundary	A surface boundary separating cooler more-dense air from warmer less-dense air. Outflow boundaries formed by the horizontal spreading of cool air that originated inside a thunderstorm. [1]
3977	Overlapping Pair	In photogrammetry, two photographs taken at different exposure stations in such a manner that a portion of one photograph shows the same terrain as shown on a portion of the other photograph. This term covers the general case and does not imply that the photographs were taken for stereoscopic examination. See also stereoscopic pair. [14]
3978	Overshooting Top	A situation in a mature thunderstorm where rising air, associated with strong convection, penetrates into a stable layer (usually the stratosphere), forcing the upper part of the cloud to rise above its relatively flat anvil top. [1]
3979	Parachute Drogue	See drogue. [14]
3980	Parallactic Grid	See grid. [14]
3981	Parallax: Linear	See parallax: absolute stereoscopic. [14]
3982	Parallel Sailing	See sailing. [14]
3983	Parallel: Ground	In photogrammetry, the intersection of the plane of the photograph with the plane of reference of the ground. See also axis of homology. [14]
3984	Particular Scale	See scale. [14]
3985	Peak Wave Period	Tp ; The wave period with the highest energy. ; Determined by the inverse of the frequency at which a wave energy spectrum reaches its maximum. ; Reciprocal of the frequency corresponding to the largest value (peak) of the frequency wave spectrum. The frequency wave spectrum is obtained by integrating the two-dimensional wave spectrum over all directions. [9][10][11]
3986	Pelagic Division	In the classification of the marine environment and its inhabitants, a primary division of the sea which includes the whole mass of water. The division is made up of the neritic province which includes that water shallower than 200 meters, and the oceanic province which includes that water deeper than 200 meters. The other primary division of the sea is the benthic division. [14]
3987	Pendulum Sextant	See sextant. [14]
3988	Periodic Current	See current. [14]
3989	Periodic Wave(S)	See wave. [14]
3990	Perspective Grid	See grid. [14]
3991	Phase Inequality	Variations in the tides or tidal currents associated with changes in the phase of the moon. [14]
3992	Phase Modulation	See modulation. [14]
3993	Photodelineation	The delineation of features on a photograph. See also compilation. [14]
3994	Photolithography	That branch of lithographic printing in which photography is employed for production of the image on the final printing surface. The original printing surface, lithographic stone, has been almost completely displaced by thin and flexible sheets of metal (zinc, aluminium, stainless steel, bimetallic plates, polymetallic plates). [14]
3995	Photozincography	The use of a zinc plate in photoengraving. [14]
3996	Piezoelectricity	The property exhibited by some asymmetrical crystalline materials which when subjected to strain in suitable directions develop electric polarization proportional to the strain. Inverse piezoelectricity is the effect in which mechanical strain is produced in certain asymmetrical crystalline materials when subjected to an external electric field; the strain is proportional to the electric field. [14]
3997	Planet(S): Major	The four largest planets (jupiter, saturn, uranus and neptune). [14]
3998	Planet(S): Minor	See asteroid. [14]
3999	Plunging Breaker	See breaker. [14]
4000	Point Of Arrival	See arrival: point of. [14]
4001	Polar Easterlies	A shallow body of easterly winds located at high latitudes poleward of the subpolar low. [1]
4002	Progressive Wave	See wave. [14]
4003	Prolate Spheroid	See spheroid. [14]
4004	Prominent Object	Objects which are easily identifiable, but do not justify being classed as conspicuous. [14]
4005	Propagated Error	An error which occurs in one operation and contaminates subsequent operations. [14]
4006	Protractor: Cust	Square or rectangular sheet of transparent xylonite engraved with a circle graduated in degrees and half degrees. Observed angles are drawn, in general, on the under side. See protractor: three arm. [14]
4007	Pulse Modulation	See modulation. [14]
4008	Radar: Secondary	See radar: primary. [14]
4009	Radio Fog Signal	See fog signal. [14]
4010	Radiobeacon Buoy	See buoy. [14]
4011	Radius: Cruising	See cruising radius. [14]
4012	Reduced Latitude	See latitude: parametric. [14]
4013	Reference Object	A well-defined object selected as a starting point in the direction method of observation. [14]
4014	Relative Bearing	See bearing. [14]
4015	Scale: Numerical	See scale: natural. [14]
4016	Scale: Principal	The scale of a reduced or generating globe representing the sphere or spheroid defined by the fractional relation of their respective radii. [14]
4017	Scales Of Motion	The hierarchy of atmospheric circulations from tiny gusts to giant storms. [1]
4018	Seasonal Current	See current. [14]
4019	Seismic Sea Wave	See tsunami. [14]
4020	Sensible Horizon	See horizon. [14]
4021	Sensitive Bubble	See level: spirit. [14]
4022	Sequence Of Tide	The order in which the tides of a day occur, with special reference to whether the higher high water immediately precedes or follows the lower low water. [14]
4023	Signal: Luminous	In surveying, a signal consisting of heliotrope or heliostat by day, and selenotrope or signal lamp by night. [14]
4024	Skew Convergence	The angle, on a skewed projection, between true north and skew north. [14]
4025	Solsticial Point	See solstice. [14]
4026	Sonic Navigation	See navigation. [14]
4027	Sounding Machine	An instrument for measuring depth of water, consisting essentially of a reel of wire to one end of which is attached a weight which carries a device for recording the depth. A crank or motor is provided for reeling in the wire. [14]
4028	Sounding: Danger	A minimum sounding chosen for a vessel of specific draft in a given area to indicate the limit of safe navigation. [14]
4029	Space Modulation	See modulation. [14]
4030	Specific Gravity	The ratio of the density of a substance at a given temperature and the density of some other substance used as a standard. For liquids and solids, the standard assumed is the density of distilled water at 4°c. [14]
4031	Spilling Breaker	See breaker. [14]
4032	State Of The Sea	See sea state. [14]
4033	Station Pressure	The actual air pressure computed at the observing station. [1]
4034	Station: Control	See control. [14]
4035	Station: Laplace	A triangulation or traverse station at which a laplace azimuth is determined. At a laplace station both astronomical longitude and astronomical azimuth are determined. [14]
4036	Stationary Front	A front that is nearly stationary with winds blowing almost parallel and from opposite directions on each side of the front. [1]
4037	Steering Compass	See compass. [14]
4038	Stellar Parallax	See parallax: annual. [14]
4039	Stereocomparator	In photogrammetry, a stereoscopic instrument for measuring parallax; usually includes a means of measuring photograph coordinates of image points. [14]
4040	Storm High Water	See high water. [14]
4041	Stream: Outgoing	See ebb stream. [14]
4042	Submarine Sentry	A form of underwater kite towed at a predetermined constant depth in search of elevations of the bottom. The kite rises to the surface upon encountering an obstruction. [14]
4043	Submarine Spring	See spring. [14]
4044	Submarine Valley	See valley. [14]
4045	Substellar Point	The geographical position of a star; that point on the surface of the earth at which the star is in the zenith at a specified time. Also called subastral point. [14]
4046	Suction Vortices	Small, rapidly rotating whirls perhaps 10 m in diameter that are found within large tornadoes. [1]
4047	Superior Transit	See meridian transit. [14]
4048	Survey: Magnetic	A survey conducted to measure the strength and direction of the earth's magnetic field at specific points on or near the surface of the earth. [14]
4049	Survey: Offshore	Hydrographic surveys conducted in areas beyond a certain distance from the shore, e.g. In the high seas. [14]
4050	Survey: Revisory	Hydrographic surveys conducted for the revision of charts including checking depths, aids to navigation, existence of land and water features, and any changes or additions such as new features constructed that are important to the mariner. A revisory survey is not considered to be a detailed resurvey. [14]
4051	Surveying: Plane	A branch of the art of surveying in which the surface of the earth is considered a plane surface. In plane surveying, curvature of the earth is neglected, and computations are made using the formulae of plane geometry and plane trigonometry. [14]
4052	Tape Thermometer	See under thermometer. [14]
4053	Telemeteorograph	General term for meteorological instruments whose indications are recorded at a distance. [14]
4054	Telltale Compass	See compass. [14]
4055	Terrestrial Pole	See pole. [14]
4056	Thermohygrograph	See hygrothermograph. [14]
4057	Tidal Prediction	See tide prediction. [14]
4058	Tide(S): Apogean	Tides of decreased range occurring when the moon is near apogee. [14]
4059	Tide: Single Day	See tide: diurnal. [14]
4060	Time: Local Mean	The mean solar time for the meridian of the observer. [14]
4061	Time: Mean Solar	Time measured by the diurnal motion of the mean sun, which is supposed to move uniformly in the celestial equator, completing the circuit in one tropical year. Often termed simply mean time. [14]
4062	Time: True Solar	See time: apparent solar. [14]
4063	Topography Board	See field board. [14]
4064	Tornado Outbreak	A series of tornadoes that forms within a particular region?a region that may include several states. Often associated with widespread damage and destruction. [1]
4065	Transit Traverse	See traverse. [14]
4066	Transition Layer	A water layer with a distinct change of the vertical gradient of a given parameter relative to adjacent layers. [14]
4067	Traverse Sailing	See sailing. [14]
4068	Traverse Station	See station. [14]
4069	Traverse: Closed	A traverse which starts and ends upon the same station, or upon stations whose relative positions have been determined by other surveys. [14]
4070	Tropic Of Cancer	The northern parallel of declination, approximately 23°27' from the celestial equator, reached by the sun at its maximum northerly declination, or the corresponding parallel on the earth. [14]
4071	Turn Of The Tide	See change of tide. [14]
4072	Underground Mark	A station mark set and plumbed below the center of a surface mark and separated therefrom so as to preserve the station in case of accident to the surface mark. Also called subsurface mark. [14]
4073	Watch: Comparing	A hack watch, particularly one having its error determined by comparison with a chronometer. [14]
4074	Water Turbulence	The disturbance of water caused by the interaction of any combination of waves, currents, tidal streams, wind, shoal patches and obstructions. [14]
4075	Wave Forecasting	The theoretical determination of future wave characteristics; usually from observed or predicted meteorological or oceanographic phenomena. [14]
4076	Wave: Modulating	A wave which modulates a carrier wave. [14]
4077	Wave: Transverse	A wave in which the direction of propagation of the wave is normal to the displacements of the medium, for example, a vibrating string. The gravity wave in which fluid parcels move in circular orbits is an example of a mixed transverse-longitudinal wave. [14]
4078	Wave: Trochoidal	A progressive oscillatory wave whose form is that of a prolate cycloid or trochoid. It is approximated by waves of small amplitudes. [14]
4079	Wave: Ultrashort	A radio wave shorter than 10 meters. [14]
4080	Wind-Chill Index	The cooling effect of any combination of temperature and wind, expressed as the loss of body heat. Also called wind-chill factor. [1]
4081	Wire Drag Survey	See survey. [14]
4082	Working Pendulum	See pendulum. [14]
4083	Zenith Telescope	See telescope. [14]
4084	Zero Sounding(S)	See sounding. [14]
4085	Zone: Equisignal	That region in space within which the difference in amplitude of two radio signals (usually emitted by a single station) is indistinguishable. [14]
4086	Absolute Accuracy	See accuracy: absolute. [14]
4087	Acoustic Sounding	See echo sounding. [14]
4088	Adjusted Position	See position. [14]
4089	Aerial Navigation	See navigation: air. [14]
4090	Alignment Of Base	The laying out of a base line in correct alignment by means of a theodolite and range poles, before the length of the line is measured. [14]
4091	Almanac: Nautical	An annual publication containing various computed astronomical data primarily intended for use in marine navigation. See also ephemeris. [14]
4092	Altitude: Sextant	The altitude as indicated by a sextant before corrections are applied. [14]
4093	Amphidromic Point	A no-tide point, from which cotidal lines radiate. [14]
4094	Anchorage Buoy(S)	Buoy(s) marking the limits of an anchorage. [14]
4095	Angle: Conversion	See arc to chord correction. [14]
4096	Annual Inequality	Seasonal variation in water level or tidal current speed, more or less periodic, due chiefly to meteorological causes. [14]
4097	Anomaly: Magnetic	See local magnetic disturbance. [14]
4098	Antenna: Screened	Any antenna which is screened in some way to counteract disturbances. [14]
4099	Apochromatic Lens	A lens that has been corrected for chromatic aberration for at least three colors. [14]
4100	Apparent Altitude	See altitude: apparent. [14]
4101	Apparent Position	See position. [14]
4102	Arc Of Visibility	The arc of a light sector designated by its limiting bearings in which a light is visible as viewed from a vessel. [14]
4103	Arc: Astronomical	The apparent arc described above (diurnal arc) or below (nocturnal arc) the horizon by the sun or another celestial body. [14]
4104	Articulated Light	See articulated beacon. [14]
4105	Artificial Island	See installation offshore. [14]
4106	Automatic Plotter	See plotter. [14]
4107	Azimuth: Geodetic	For the geodesic line from a to b, the angle between the tangent to the meridian at a and the tangent to the geodesic line at a. This azimuth is called the forward azimuth for the line ab. See azimuth: back. [14]
4108	Azimuth: Magnetic	At the point of observation, the angle between the vertical plane through the observed object and the vertical plane in which a freely suspended symmetrically magnetized needle, influenced by no transient artificial magnetic disturbance, will come to rest. [14]
4109	Band Of Frequency	The range of frequency between two specific limits. Also called frequency band. [14]
4110	Barometer: Marine	Mercury barometer used on board ships, characterized by a constriction in the tube in order to damp out oscillations of the mercury caused by the movements of the ship. [14]
4111	Basal Orientation	See orientation. [14]
4112	Beacon: Responder	See transponder beacon. [14]
4113	Bearing: Acoustic	See bearing: sonic. [14]
4114	Bearing: Magnetic	Bearing relative to magnetic north. Compass bearing corrected for magnetic deviation. [14]
4115	Bearing: Relative	Bearing relative to the heading of a craft. [14]
4116	Bessel'S Spheroid	See reference spheroid. [14]
4117	Boundary Monument	A material object placed on or near a boundary line to preserve and identify the ground location of the boundary line. Where it is impracticable to establish a monument on or very close to a boundary line, the position of the boundary line on the ground is preserved by means of reference marks. The term monument is sometimes used to include both the mark on the boundary and the reference mark. [14]
4118	Breaking Of Waves	Disintegration of a wave which breaks with foam in shallows whose gradient is more or less regular. An incomplete breaking can likewise result from a sudden reduction in depth. [14]
4119	Broad On The Beam	Bearing 090° relative (broad on the starboard beam) or 270° relative (broad on the port beam). If the bearings are approximate, the expression on the beam or abeam should be used. See also on the beam. [14]
4120	Buoy: Bifurcation	A distinctive lateral buoy used to indicate both the point at which a channel divides and the channel that has been designated as preferred channel. [14]
4121	Buoy: Radiobeacon	A buoy equipped with a marker radio beacon. [14]
4122	Cable: Degaussing	Cable carrying an electric current for degaussing a vessel. [14]
4123	Camera: Ballistic	A precision terrestrial camera usually employing glass plates, used at night to photograph such objects as rockets or satellites against a star background. If the camera is mounted so that it tracks the stars or the object, it may be called a tracking camera. [14]
4124	Canyon: Submarine	A relatively narrow, deep depression with steep slopes, the bottom of which grades continuously downward. [14]
4125	Celestial Concave	See celestial sphere. [14]
4126	Centripetal Force	The force directed towards the center of curvature which constrains a body to move in a curved path. Equal and opposite to the centrifugal force. [14]
4127	Chart Compilation	The production of a new or revised map or chart, or portions thereof, from existing maps, aerial photographs, surveys, new data and other sources or the selection, assembly, and graphic representation of all relevant information required for the preparation of a map or chart. [14]
4128	Clamshell Snapper	See snapper. [14]
4129	Clarke'S Spheroid	See reference spheroid. [14]
4130	Clearance: Bridge	Minimum vertical or horizontal space available for passage. [14]
4131	Climatic Controls	The relatively permanent factors that govern the general nature of the climate of a region. [1]
4132	Closure: Error Of	See error of closure. [14]
4133	Collector Tracing	A comprehensive record of the work compiled while the hydrographic survey is in progress. [14]
4134	Colour Separation	Either the process of preparing a separate drawing, engraving or negative for each colour required in the production of a chart or a photographic process or electronic scanning procedure using colour filters to separate a multi-colored copy into separate images of each of the three primary colors. [14]
4135	Compass Needle(S)	Magnetized steel needle(s) of high retentivity that tends to keep north-south line of compass card in magnetic meridian. [14]
4136	Compass: Deadbeat	An aperiodic compass; one that, when deflected, returns by one direct movement to its proper reading. [14]
4137	Compass: Inverted	See compass: hanging. [14]
4138	Compass: Magnetic	A compass depending for its directive force upon the attraction of the magnetism of the earth for a magnet free to turn in an horizontal direction. [14]
4139	Compass: Overhead	See compass: hanging. [14]
4140	Compass: Standard	A compass designated as the standard for a vessel. It is located in a favorable position and is accurately calibrated. [14]
4141	Composite Sailing	See sailing. [14]
4142	Computer: Digital	A machine for carrying out mathematical processes by operations based on counting, as distinct from an analogue computer. [14]
4143	Control: Geodetic	A system of control stations established by geodetic methods. See survey: geodetic. [14]
4144	Control: Vertical	Control determined in elevation relative to a datum plane. [14]
4145	Controlling Depth	See depth. [14]
4146	Conversion Factor	That factor by which the numerical value made in one system of units must be multiplied to arrive at the numerical value in another system of units. [14]
4147	Coordinates: Grid	A plane rectangular coordinate system based on, and mathematically adjusted to, a map projection, so that geographic positions in terms of latitude and longitude can be readily transformed into plane coordinates, and the computation relating to them made by the ordinary methods of plane surveying. [14]
4148	Critical Sounding	The least depth in proximity to a known or potential navigational route. [14]
4149	Current: Backrush	A gradient current caused by the rise of water level near shores and in sea reaches. [14]
4150	Current: Gradient	A current due to the horizontal component of the hydrostatic pressure gradient. [14]
4151	Current: Nontidal	Any current that is caused by other than tide producing forces. See also stream. [14]
4152	Current: Periodic	An oscillating current the values of which recur at somewhat regular intervals. [14]
4153	Current: Residual	The mean current without periodic components. [14]
4154	Current: Seasonal	A current which has large changes in speed or direction due to seasonal winds. [14]
4155	Day: Astronomical	A mean solar day beginning at noon. [14]
4156	Declination: Grid	See grid. [14]
4157	Depth Differences	Those differences in depth which may be encountered in hydrographic surveys at crossing of cross lines and principal lines of soundings. [14]
4158	Detached Position	See position. [14]
4159	Detached Sounding	See sounding. [14]
4160	Difference: Tidal	See tidal difference. [14]
4161	Differential Mode	A method of accurate positioning; transmissions of an electromagnetic position fixing system are received at known positions ashore and the offsets between absolute known positions and system positions are transmitted to the ship in the vicinity. The offsets are applied to the measurements of the ship's receiver. [14]
4162	Direction Of Tilt	The direction (azimuth) of the principal plane of a photograph. Also, the direction of the principal line on a photograph. [14]
4163	Direction Of Wind	Direction from which the wind blows. Also called wind direction. [14]
4164	Dissipating Stage	The final stage in the development of an ordinary cell thunderstorm when downdrafts exist throughout the cumulonimbus cloud. [1]
4165	Double High Water	See high water. [14]
4166	Doubtful Sounding	See sounding. [14]
4167	Ecliptic Latitude	See latitude: celestial. [14]
4168	Eotvos Correction	A correction applied to gravity measurements to balance the effect of the vertical force experienced by a body moving in an east-west direction on the rotating earth. [14]
4169	Equation: Laplace	An equation which expresses the relationships between astronomic azimuth, geodetic azimuth, and the astronomic longitude and geodetic longitude. [14]
4170	Equator: Geodetic	The line on the spheroid connecting points of 0° geodetic latitude. [14]
4171	Equator: Magnetic	That line on the surface of the earth connecting all points at which the magnetic dip is zero. Also called aclinic line. [14]
4172	Equidistance Line	See median line. [14]
4173	Equinoctial Point	See equinox. [14]
4174	Erecting Eyepiece	See eyepiece. [14]
4175	Error: Accidental	An error whose occurrence depends on the law of chance only. Also calledrandom erroror irregular error. [14]
4176	Error: Systematic	An error whose magnitude changes in proportion to known changes in observational conditions. Also called regular error. [14]
4177	Evaluation Report	A report which summarizes pertinent facts relating to a given hydrographic survey. Included in the report are sections which address the quality of the hydrographic survey and detailed comparisons made with prior hydrographic surveys and the appropriate nautical chart. Specific evaluations and recommendations regarding the adequacy of the survey to supersede prior survey data and charted information are made. [14]
4178	Exposure Interval	The time interval between the taking of successive photographs. [14]
4179	First Nodal Point	See nodal point. [14]
4180	Focal-Plane Plate	A glass plate set in the camera so that the surface away from the lens coincides with the focal plane. Its purpose is to position the emulsion of the film in the focal plane when the film is physically pressed into contact with the glass plate. Also called contact glass or contact plate. [14]
4181	Fog Signal: Radio	A regularly recurring distinctive signal sent out by a radio beacon during thick weather. [14]
4182	Forced Convection	See convection. [14]
4183	Frequency Channel	See channel. [14]
4184	Front Nodal Point	See nodal point. [14]
4185	Geodetic Position	See position. [14]
4186	Geologic(Al) Time	See time. [14]
4187	Grid: Parallactic	In photogrammetry, a uniform pattern of rectangular lines drawn or engraved on some transparent material, usually glass, and placed either over the photographs of a stereoscopic pair or in the optical system of a stereoscope, in order to provide a continuous floating-mark system. [14]
4188	Grid: Perspective	In photogrammetry, a network of lines, drawn or superimposed on a photograph, to represent the perspective of a systematic network of lines on the ground or datum plane. See also grid method. [14]
4189	Groin (Or Groyne)	A low artificial wall-like structure of durable material extending from the land to seaward for a particular purpose, such as to protect the coast or to force a current to scour a channel. Sometimes called arip-rap in new england waters. [14]
4190	Ground Resolution	See resolution. [14]
4191	Hemispherical Map	See map. [14]
4192	High Water: Storm	The highest level to which the sea rises during a storm and usually marked by a line of debris high up on the beach. [14]
4193	Horizon: Rational	See horizon: celestial. [14]
4194	Horizon: Sensible	That circle of the celestial sphere formed by the intersection of the celestial sphere and a plane through any point, such as the eye of an observer, and perpendicular to the zenith-nadir line. [14]
4195	Hurricane Hunters	A popular term for aircraft and/or personnel engaged in the reconnaissance of hurricanes (tropical cyclones). [1]
4196	Hurricane Warning	A warning given when it is likely that a hurricane will strike an area within 24 hours. [1]
4197	Hydrologic Series	Simultaneous observations carried out to obtain oceanographic data at specified levels. [14]
4198	Hypsometric Curve	See hypsographic curve. [14]
4199	Hypsometric Tints	A succession of shades or colour graduations used to depict ranges of elevations. Also called gradient tints or elevation tints. [14]
4200	Ice Concentration	In sea ice reporting, the ratio of the areal extent of ice present to the total areal extent of ice and water. Concentration is usually reported in tenths. Also called ice cover. [14]
4201	Ionospheric Storm	Violent changes in the state of the ionosphere. [14]
4202	Isostatic Anomaly	The difference between an observed value of gravity and a theoretical value at the point of observation which has been corrected for elevation of the station above the geoid and for the effect of topography over the whole earth, and for its isostatic compensation. [14]
4203	Labour (Or Labor)	(v.i.). To pitch and roll heavily under conditions which subject the ship to unusually heavy stresses caused by confused or turbulent seas or unstable stowage or cargo. [14]
4204	Lake-Effect Snows	Localized snowstorms that form on the downwind side of a lake. Such storms are common in late fall and early winter near the great lakes as cold, dry air picks up moisture and warmth from the unfrozen bodies of water. [1]
4205	Latitude: Reduced	See latitude: parametric. [14]
4206	Level: Bull'S Eye	See level: spirit. [14]
4207	Levelling: Direct	The determination of differences of elevation by a continuous series of short horizontal lines. Vertical distances from these lines to adjacent ground marks are determined by direct observations on graduated rods with a levelling instrument equipped with a spirit level. [14]
4208	Levelling: Spirit	The determination of elevations of points with respect to each other or with respect to a common datum, by use of a levelling rod and an instrument using a spirit level to establish a horizontal line of sight. [14]
4209	Light(S): Leading	Two or more lights associated so as to form a leading line to be followed. [14]
4210	Light: Aeromarine	A marine-type light in which a proportion of the beam is deflected to an angle of 10°-15° above the horizon for the use of aircraft. [14]
4211	Light: Morse Code	A rhythmic light in which appearances of light of two clearly different durations are grouped to represent a character or characters in the morse code. [14]
4212	Light: Occasional	A light not regularly exhibited. [14]
4213	Light: Undulating	A continuously luminous light which alternatively increases and decreases in brightness in cyclic sequence. [14]
4214	Longitudinal Wave	See wave. [14]
4215	Low Water: Double	A low water consisting of two minima separated by a relatively small elevation. See tide: double. [14]
4216	Lower Culmination	See meridian transit. [14]
4217	Magnetic Latitude	See latitude. [14]
4218	Marine Stabilizer	See stabilizer. [14]
4219	Mean Sphere Depth	The uniform depth to which the water would cover the earth if the solid surface were smoothed off and were parallel to the surface of the geoid. The accepted figure for this depth is 2,440 meters. The mean depth of the sea is 3,800 meters. [14]
4220	Mean Spring Range	See spring range. [14]
4221	Mean Square Error	See error. [14]
4222	Measured Distance	A course at sea, whose ends are indicated by ranges ashore, and whose length has been accurately measured for determining the speed of vessels. [14]
4223	Mercury Barometer	A type of barometer that uses mercury to measure atmospheric pressure. The height of the mercury column is a measure of atmospheric pressure. [1]
4224	Meridian: Central	See meridian: initial. [14]
4225	Meridian: Compass	A line through the north-south points of a magnetic compass. The compass card axis lies in the compass meridian. [14]
4226	Meridian: Initial	A meridian through the origin of a system of grid coordinates and used as y-axis of the system. Also called central meridian. [14]
4227	Method Of Squares	See squares: method of. [14]
4228	Micrometer: Filar	A device attached to a telescope or microscope, consisting of a wire thread (filament) connected with a screw in such manner that as the screw is turned, the wire moves through a continuous succession of parallel positions, all in the focal plane of the instrument. Any small angle may be measured by noting the number of turns and fractions of a turn of the screw which are made in moving the wire from one bisection to another, and multiplying this by the value of one turn. See micrometer: ocular, micrometer microscope, and micrometer comb. [14]
4229	Modulation: Pulse	The process of forming very short bursts of a carrier wave, separated by relatively long periods during which no carrier wave is transmitted. [14]
4230	Modulation: Space	The combining of signals in space to form a signal of desired characteristics. [14]
4231	Moment Of Inertia	The quantity obtained by multiplying the mass of each small part of a body by the square of its distance from an axis, and adding all the results. [14]
4232	Multiple Echo(Es)	See echo. [14]
4233	Nadir: Photograph	In photogrammetry, the point at which a vertical line through the perspective center of the camera lens pierces the plane of the photograph. Also called nadir point, or plumb point. [14]
4234	Natural Frequency	See frequency. [14]
4235	Nautical Twilight	See twilight. [14]
4236	Navigation: Astro	See navigation: celestial. [14]
4237	Navigation: Radio	See navigation: electronic. [14]
4238	Negative Gradient	In oceanography, a layer of water where temperature decreases with depth. [14]
4239	Nitric Oxide (No)	A colorless gas produced by natural bacterial action in soil and by combustion processes at high temperatures. In polluted air, nitric oxide can react with ozone and hydrocarbons to form other substances. In this manner, it acts as an agent in the production of photochemical smog. [1]
4240	No-Check Position	See station: intersection. [14]
4241	Nodal Point: Rear	See nodal point. [14]
4242	Observation Tower	A tower from which one's surroundings can be observed, but at which a watch is not habitually maintained, as at a lookout tower. Such towers are temporarily erected for observations in geodetic networks. [14]
4243	Obstruction Light	See light. [14]
4244	Ocular Micrometer	See micrometer. [14]
4245	Opacity (Optical)	The ratio of the incident to the transmitted (or reflected) light. It varies with the use of scattered or specular light. [14]
4246	Open End Traverse	See traverse: open. [14]
4247	Orographic Uplift	The lifting of air over a topographic barrier. Clouds that form in this lifting process are called orographic clouds. [1]
4248	Pair Of Compasses	See compass. [14]
4249	Parallactic Error	See error. [14]
4250	Parallax: Angular	See parallactic angle. [14]
4251	Parallax: Optical	See parallax: instrumental. [14]
4252	Parallel Sounding	A system of surveying in which the mother vessel takes soundings while following a given course; at the same time an array of satellite boats takes soundings along parallel courses at a fixed distance from the mother vessel. The satellite boats determine their position relative to the mother vessel. The term is also employed when a single vessel takes multiple lines of soundings with transducers arranged at regular intervals on outriggers. [14]
4253	Particle Velocity	In ocean wave studies, the instantaneous velocity of a water particle undergoing orbital motion. At the crest, its direction is the same as the direction of progress of the wave, and at the trough it is in the opposite direction. [14]
4254	Passage: Meridian	See meridian transit. [14]
4255	Pendulum: Working	A pendulum which is used (swung) in a determination of the intensity of gravity. [14]
4256	Permanent Current	See current. [14]
4257	Photograph Centre	The center of a photograph as indicated by the images of the fiducial mark or marks of the camera. In a perfectly adjusted camera the photograph center and the principal point are identical. [14]
4258	Photohead Plotter	A device used to plot information by exposure of a photographic film. [14]
4259	Pinnacled Iceberg	An iceberg weathered in such manner as to produce spires or pinnacles. Also called pyramidal iceberg, irregular iceberg. [14]
4260	Plane: Horizontal	A plane perpendicular to the direction of gravity; any plane tangent to the geoid or parallel to such a plane. In surveying, a plane perpendicular to the plumb line within which or on which angles and distances are observed. [14]
4261	Pole: Terrestrial	One of the poles of the earth. See pole. [14]
4262	Position Doubtful	Of uncertain position. The expression is used principally on charts to indicate that a wreck, shoal, etc., has been reported in various positions and not definitely determined in any. Usually shown by the abbreviation 'pd'. [14]
4263	Position: Assumed	A point at which a craft is assumed to be located, particularly one used as preliminary to establishing certain navigational data, as that point of the surface of the earth for which the computed altitude is determined in the solution of a celestial observation. [14]
4264	Positive Gradient	In oceanography, a positive rate of change with depth. [14]
4265	Potential Density	In oceanography, the density that a parcel of water would have if raised adiabatically to the surface, that is, if determined from the parcel's 'in situ' salinity and potential temperature. [14]
4266	Predicted Tide(S)	See tide. [14]
4267	Pressure-Altitude	An atmospheric pressure expressed in terms of altitude which corresponds to that pressure in the standard atmosphere. [14]
4268	Quadrantal Sphere	See quadrantal correctors. [14]
4269	Radial Distortion	See under distortion. [14]
4270	Radio Time Signal	A time signal sent by radio. [14]
4271	Radio Transmitter	Equipment for generating radio signals. [14]
4272	Recommended Route	See route: recommended. [14]
4273	Refraction: Angle	See angle of refraction. [14]
4274	Relative Accuracy	See accuracy: relative. [14]
4275	Relative Aperture	See aperture: relative. [14]
4276	Relief: Submarine	Inequalities of the ocean bed, or their representation on a chart. [14]
4277	Resection Station	See station. [14]
4278	Reversing Current	See current. [14]
4279	Roll (Or Rolling)	The oscillation of a ship about the longitudinal axis. In photogrammetry, a rotation of a camera or a photograph-coordinate system about either the photograph x axis or the exterior x axis. [14]
4280	Sailing: Mercator	A mathematical solution of the plot as made on a Mercator chart. It is similar to plane sailing, but uses meridional difference and difference of longitude in place of difference of latitude and departure, respectively. [14]
4281	Sailing: Meridian	Following a true course of 0° or 180°; sailing along a meridian. [14]
4282	Sailing: Parallel	A method of converting departure into difference of longitude, or vice versa, when the true course is 90° or 270°. [14]
4283	Sailing: Traverse	A method of determining the equivalent course and distance made good by a craft following a track consisting of a series of rhumb lines. The problem is customarily solved by the principles of plane sailing. [14]
4284	Saint Elmo'S Fire	Faintly luminous electrical discharge in the atmosphere: this discharge, more or less continuous and of slight or moderate intensity, emanates from objects which present a high surface electric field, in particular from points and sharp edges. [14]
4285	Satellite Geodesy	See geodesy. [14]
4286	Satellite Station	See eccentric station. [14]
4287	Scale: Equivalent	The relationship which a small distance on a map, chart or graphic bears to the corresponding distance on the earth, expressed as an equivalence. [14]
4288	Scale: Fractional	See scale: natural. [14]
4289	Scale: Log Factor	In hydrographic surveys, a proportional diagram constructed for the scale of the survey sheet by means of which the log factor can be quickly determined. [14]
4290	Scale: Particular	The relation between an infinitesimal linear distance in any direction at any point on a map projection and the corresponding linear distance on a globe. [14]
4291	Seabed Topography	See topography. [14]
4292	Secondary Station	See station: supplementary. [14]
4293	Secondary Tide(S)	See tide. [14]
4294	Sector Scan Sonar	A horizontal aperture sonar used to detect obstructions ahead of the vessel by mechanical or electronic scanning in the horizontal plane. [14]
4295	Sedimentary Rocks	Rocks formed by the accumulation of sediment in water (aqueous deposits) or from air (eolian deposits). The sediments may consist of rock fragments or particles of various sizes (conglomerate, sandstone, shale); of the remains or products of animals or plants (certain limestones and coal); of the product of chemical action or of evaporation (salt, gypsum, etc.); or of mixture of these materials. [14]
4296	Semi-Arid Climate	A dry climate where potential evaporation and transpiration exceed precipitation. Not as dry as the arid climate. Typical vegetation is short grass. [1]
4297	Semi-Enclosed Sea	See enclosed sea. [14]
4298	Separation Effect	In echo sounding instruments with separate transmitting and receiving units, the effect caused by such separation. This introduces an error depending on the distance between the acoustic units and varying with the depth of water. Such error makes the registered depth greater than the actual depth. Separation also causes a lag in registration of the transmitted signal. [14]
4299	Sextant: Pendulum	A sextant provided with a pendulum to indicate the horizontal. [14]
4300	Sextometer Method	A substitute for plane table traverse for short distances in unimportant areas where the use of the plane table is impracticable and the survey party operates in a launch. Azimuth is carried forward by means of angles accurately measured with a sextant. Distance is determined by measuring, also with the sextant, the small horizontal angle between fixed targets on a special rod held horizontally. The angle may be converted into a distance by means of a hypsography. [14]
4301	Signal: Eccentric	See eccentric signal. [14]
4302	Signal: Longitude	A sign indicating a time event, observable at different stations, and used in comparing local times of those stations, and determining the difference of their longitudes. [14]
4303	Skewed Projection	See projection. [14]
4304	Small Craft Chart	Chart designed for easy reference and plotting in limited spaces. It portrays regular nautical chart detail and other specific details of special interest to the small craft operator, such as enlargements of harbors; tide, current and weather information; rules of the road information; locations of marine facilities; anchorages; courses; and distances. [14]
4305	Solsticial Colure	See colure: solsticial. [14]
4306	Sounding Interval	The interval between successive soundings along a line of sounding. See density of soundings. [14]
4307	Sounding(S): Zero	(US Terminology). Soundings that reduce to heights above the sounding datum but shown on the smooth sheet as zero soundings regardless of height. A practice now discontinued. See sounding: minus. [14]
4308	Sounding: Line Of	See line of sounding. [14]
4309	Space Coordinates	See coordinates. [14]
4310	Spherical Sailing	See sailing. [14]
4311	Spoil Ground Buoy	A buoy marking the limit of a spoil ground. [14]
4312	Station: Magnetic	The geographic location at which any set of magnetic observations was taken. [14]
4313	Station: Traverse	A definite point on the earth whose position has been determined from another known point by linear measurements controlled in azimuth by angular measurements. [14]
4314	Steering Repeater	A compass repeater by which a craft is steered. See also compass: steering. [14]
4315	Stereocompilation	See compilation. [14]
4316	Still Water Level	The level that the sea surface would assume in the absence of wind waves; not to be confused with mean sea level or half-tide level. [14]
4317	Submarine Volcano	A seabed volcano, submerged at the chart sounding datum, which may or may not be active. [14]
4318	Substitute Centre	A point which, because of its ease of identification on overlapping photographs, is used instead of the principal point as a radial center. [14]
4319	Sunshine Recorder	See heliograph. [14]
4320	Survey: Cadastral	A survey relating to land boundaries and subdivisions, made to create units suitable for transfer or to define the limitations of title. Also called land survey. [14]
4321	Survey: Wire-Drag	A hydrographic survey made utilizing a wire drag. In areas of rocky bottom or where submerged obstacles such as wrecks are present, a wire-drag survey represents the most practical way of making sure that all obstructions or dangers have been found and least depths over them obtained. Also called wire drag sweep. [14]
4322	Surveying Sextant	See sextant: sounding. [14]
4323	Synoptic Analysis	See weather analysis. [14]
4324	Synoptic Forecast	Weather forecast based on synoptic observation. [14]
4325	Taut Wire Mooring	A mooring arrangement in which a submerged float provides the upward force necessary to maintain the system in a fixed position with reference to the sea bottom. [14]
4326	Telescope: Zenith	An astronomical instrument for determining the latitude by observing zenith distances of two stars that culminate as close as possible in time, and at nearly the same altitude on opposite sides of the zenith. [14]
4327	Terrestrial Globe	See globe. [14]
4328	Theoretical Error	See error. [14]
4329	Thermometer: Tape	A precision thermometer fitted in a specially designed case to clip on and against a metal tape in order to determine temperature corrections for precision base or traverse tape measurements. [14]
4330	Tide(S): Perigean	Tides of increased range occurring when the moon is near perigee. [14]
4331	Tide: Equilibrium	A hypothetical tide based upon the assumption that the water responds, instantly to the tide-producing forces of the moon and sun, and forms a surface of equilibrium under the action of these forces, disregarding friction, inertia and the irregular distribution of the land masses. [14]
4332	Tide: Mid-Extreme	A level midway between the extreme high water and extreme low water occurring at a place. See half-tide level. [14]
4333	Tide: Semidiurnal	A tide in which the tidal cycle consists of two high waters and two low waters each tidal day, with comparatively little diurnal inequality. [14]
4334	Topographic Model	See relief model. [14]
4335	Traverse: Hanging	See traverse: open. [14]
4336	Traverse: Transit	A traverse in which the angles are measured with a transit or theodolite and the lengths with a suitable measuring device. [14]
4337	Triangle Of Error	See cocked hat. [14]
4338	Turbidity Current	See current. [14]
4339	Upper Culmination	Upper transit. [14]
4340	Urban Heat Island	The increased air temperatures in urban areas as contrasted to the cooler surrounding rural areas. [1]
4341	Valley: Submarine	A relatively shallow wide depression, the bottom of which usually has a continuous gradient. This term is generally not used for features that have canyon-like characteristics for a significant portion of their extent. [14]
4342	Vertical Light(S)	See light. [14]
4343	Vertical Parallax	See parallax: y-. [14]
4344	Wave Interference	The phenomenon which results when waves of the same or nearly the same frequency are superposed. It is characterized by a spatial or temporal distribution of amplitude of some specified characteristic differing from that of the individual superposed waves. [14]
4345	Wave(S): Periodic	Waves which are repeated at regular intervals. [14]
4346	Wave: Oscillatory	A wave in which each individual particle oscillates about a point with little or no permanent change in position. The term is commonly applied to progressive oscillatory waves in which only the form advances, the individual particles moving in closed orbits, as ocean waves in deep waters. Distin-guished from a wave of translation. [14]
4347	Wave: Progressive	A wave which is manifested by the progressive movement of the wave form. The opposite is a standing wave. Also called travelling wave. [14]
4348	Wave: Propagation	The travel of waves through or along a medium. [14]
4349	Well: Development	A borehole drilled, usually from a production platform, after an oil field or gas field has been judged capable of economic production. [14]
4350	Year: Anomalistic	The period of one revolution of the earth around the sun, from perihelion to perihelion, averaging 365 days, 6 hours, 13 minutes, 53.0 seconds in 1900, and increasing at the rate of 0.26 second per century. [14]
4351	Accuracy: Absolute	The evaluation of all errors encountered in defining the position of a single feature or point on a geodetic datum or system. [14]
4352	Accuracy: Relative	The evaluation of the random errors in determining the positional orientation of one point or feature with respect to another. [14]
4353	Aeronautical Chart	See chart. [14]
4354	Altitude: Meridian	The altitude of a celestial body when it is on the celestial meridian of the observer. [14]
4355	Altitude: Observed	The sextant altitude of a celestial body after all corrections (see altitude: apparent) have been applied. In american terminology the term is usually employed in the place of true altitude. [14]
4356	Angle: Parallactic	See parallactic angle. [14]
4357	Angular Distortion	See distortion. [14]
4358	Aperture: Relative	For a photographic or telescopic lens, the ratio of the equivalent focal length to the diameter of the entrance pupil. Expressed as f: 4.5; also called f-number, f-stop, or speed of lens. [14]
4359	Apparent Solar Day	See day: solar. [14]
4360	Archipelagic Apron	A gentle slope with a generally smooth surface of the sea floor, characteristically found around groups of islands or seamounts. [14]
4361	Area To Be Avoided	A routing measure comprising an area within defined limits in which either navigation is particularly hazardous or it is exceptionally important to avoid casualties and which should be avoided by all ships, or certain classes of ships. [14]
4362	Articulated Beacon	A vertical pipe structure that oscillates around a universal coupling connected to a sinker. The structure is kept upright by the buoyancy of a submerged floating chamber. Primarily designed to mark narrow channels with greater precision than conventional buoys. [14]
4363	Astronomic(Al) Arc	See arc. [14]
4364	Astronomic(Al) Day	See day. [14]
4365	Atmospheric Models	Simulation of the atmosphere's behavior by mathematical equations or by physical models. [1]
4366	Atmospheric Window	The region in the radiation spectrum containing wavelengths between 8.5 and 11 micrometers, which are not absorbed to any great extent by atmospheric gases. In the absence of cloud, terrestrial radiation of this wavelength is lost to space, enabling the cooling of the earth to take place. Other narrower wavebands also do not absorb long-wave radiation, but these are of less importance in this context. [14]
4367	Barometer: Aneroid	Barometer whose sensitive element comprises one or a series of aneroid capsules. [14]
4368	Base Height Ration	In photogrammetry, the ratio between the air base and the flight altitude of a stereoscopic pair of photographs. [14]
4369	Baseline: Straight	Straight baselines are a system of straight lines joining specified or discrete points on the low-water line, usually known as straight baseline turning points. Straight baselines are used in delimitation. [14]
4370	Bucket Temperature	Temperature of surface sea water trapped and measured in a bucket or similar receptacle. [14]
4371	Cassini Projection	See projection. [14]
4372	Channel: Frequency	A continuous portion of the frequency spectrum appropriate for a transmission utilizing a specified class of emission. [14]
4373	Character Of Light	The distinct character, such as fixed, flashing, or occulting, which is given to each light to avoid confusion with neighbouring ones. [14]
4374	Chart: Bathymetric	A topographic chart of the bed of a body of water, or a part of it. Generally, bathymetric charts show depths by contour lines and gradient tints. [14]
4375	Chart: Geophysical	A chart which primarily shows parameters of geophysical nature. [14]
4376	Chart: Layer Depth	A chart showing the synoptic distribution of layer depths. [14]
4377	Chart: New Edition	See new edition (of chart). [14]
4378	Chart: Provisional	A special chart, usually for which there is an urgent need. The chart is compiled from approved source materials and may be drafted for direct reproduction. All charted information is usually combined on the black printing plate and no other colors are shown. [14]
4379	Circle Of Position	The small circle on the surface of the earth on which an observation shows the observer to be. The expression is most frequently used to indicate the circle of equal altitude. Also called position circle. [14]
4380	Circle: Horizontal	In a surveying instrument, the graduated circle used for measuring horizontal angles. [14]
4381	Coastal Refraction	See refraction. [14]
4382	Colure: Solsticial	The hour circle through the solstices. [14]
4383	Compacted Ice Edge	A close, clear-cut ice edge compacted by wind or current. It is usually on the windward side of an area of pack ice. [14]
4384	Compasses: Pair Of	See compass. [14]
4385	Compensating Coils	The coils placed near a magnetic compass to neutralize the effect of the vessel's degaussing system on the compass. [14]
4386	Compensation Depth	See depth. [14]
4387	Compression Ratios	See flattening of the earth. [14]
4388	Computer: Analogue	A physical device or system which behaves in a manner analogous to some system under study, simulating the processes and producing results which are measured in terms of physical quantities. Often an electrical system. [14]
4389	Concentration: Ice	See ice. [14]
4390	Condensation Level	The level above the surface marking the base of a cumuliform cloud. [1]
4391	Constant Deviation	See deviation. [14]
4392	Convection: Forced	In the atmosphere, convection caused by mechanical forces, such as those arising from air motion over a rough or sloping surface. [14]
4393	Coordinates: Polar	A system of coordinates used to describe the position of a point in space with respect to an arbitrarily chosen origin by means of two directions and one distance; i.e., the vectorial angles and radius vector magnitude. [14]
4394	Coordinates: Space	In photogrammetry the term may refer to any general three-dimensional coordinate system used to define the position of a point in the object space, as distinguished from the image of the same point on a photograph. [14]
4395	Coordinates: Strip	The coordinates of any point in a strip, whether on the ground or actually an air station, referred to the origin and axes of the air coordinate system of the first overlap. [14]
4396	Correlate Equation	See equation: correlate. [14]
4397	Course Over Ground	The direction of the path over the ground actually followed by a vessel. It is normally a somewhat irregular line. This is a misnomer in that courses are directions steered or intended to be steered through the water with respect to a reference meridian. Also called track over ground. [14]
4398	Current Difference	The difference between the time of slack water or strength of current at a subordinate station and at its reference station. [14]
4399	Current: Ocean/Sea	A movement of ocean water characterized by regularity, either of a cyclic nature or as a continuous stream flowing along a definable path. [14]
4400	Current: Permanent	A current which continues with relatively little periodic or seasonal change. [14]
4401	Current: Turbidity	A highly turbid, relatively dense current carrying large quantities of clay, silt and sand in suspension which flows down a submarine slope through less dense sea water. [14]
4402	Datum For Sounding	See datum: sounding. [14]
4403	Declination Circle	See hour circle. [14]
4404	Deep-Draught Route	A route which is primarily selected for use by ships which, because of their deep draught, may not be able to navigate safely outside such route. [14]
4405	Depression Contour	See contour. [14]
4406	Depth: Controlling	The least depth in the approach or channel to an area, such as a port or anchorage, governing the maximum draft of vessels that can enter. [14]
4407	Dip Of The Horizon	See dip. [14]
4408	Distance Reduction	See reduction to sea level. [14]
4409	Distortion: Radial	A lens aberration that is corrected on the photograph by displacing the image along a radial line from the principal point. [14]
4410	Doppler Navigation	See navigation. [14]
4411	Draft (Or Draught)	The vertical distance, at any section of a vessel from the surface of the water to the bottom of the keel. When measured at or near the bow, it is referred to as draft forward and when measured at or near the stern as draft aft. The mean draft is the mean of the drafts forward and aft. These drafts are more specifically described as displacement drafts as opposed to navigational drafts which are measured to the lowest appendage to the hull as opposed to the keel. [14]
4412	Echo(Es): Multiple	In echo sounding, any of the echoes received subsequent to the first one and due to a multiplicity of reflections back and forth between the bottom and surface. These reflections often register on the dial of a usual indicator, or on the fathogram of a graphic recorder, at multiplies of the true depth. Such echoes are sometimes mistaken for the first echo. [14]
4413	Elevation Of Sight	Also called height of eye. The visibility distances are relevant with the elevation of the observer's sight. When measuring a long distance by optics a line of sight should be maintained over the convex curvature of the earth and all obstacles between the measuring points. [14]
4414	Equation: Personal	See personal equation. [14]
4415	Equator: Celestial	The great circle on the celestial sphere whose plane is perpendicular to the axis of the earth. Also called equinoctial. [14]
4416	Equatorial Tide(S)	See tide. [14]
4417	Equinoctial Colure	See colure. [14]
4418	Error: Mean Square	The quantity whose square is equal to the sum of the squares of the individual errors divided by the number of those errors. [14]
4419	Error: Parallactic	An error caused by personal or instrumental parallax. [14]
4420	Error: Theoretical	A systematic error arising from natural physical conditions, beyond the control of the observer. Also called external error. [14]
4421	Existence Doubtful	Of uncertain existence. The expression is used principally on charts to indicate the possible existence of a rock, shoal, etc., the actual existence of which has not been established. Usually shown by the abbreviation 'ed'. [14]
4422	Exploratory Survey	See survey. [14]
4423	Eye (Of Hurricane)	A region in the center of a hurricane (tropical cyclone) where the winds are light and skies are clear to partly cloudy. [1]
4424	Floe (Or Ice Floe)	A piece of sea ice other than fast ice. Floes over 10 km across are described as vast; those between 1 and 10 km across as big; those between 200 and 1,000 m across as medium; those between 10 and 200 m across as small. Floes less than 10 m across are called ice cakes. [14]
4425	Fog Detector Light	A light used to automatically determine conditions of visibility which warrant the turning on or off of a sound signal. [14]
4426	Formation Sounding	See sounding. [14]
4427	Frequency: Natural	The lowest resonant frequency of a body or system. [14]
4428	Gas Chromatography	An analysis method used to determine dissolved oxygen and nitrogen content of sea water. [14]
4429	Geodesy: Satellite	The discipline which employs observations of an earth satellite to extract geodetic information. [14]
4430	Geodetic Levelling	See levelling. [14]
4431	Geology: Submarine	A field of study which applies the science of geology to the earth beneath the sea. [14]
4432	Gravimetric Survey	See survey. [14]
4433	Gravity: Centre Of	A point at which the mass of the entire body may be regarded as being concentrated. [14]
4434	Great Circle Chart	See chart: gnomonic. [14]
4435	Great Tropic Range	See range. [14]
4436	Growing Degree-Day	A form of the degree-day used as a guide for crop planting and for estimating crop maturity dates. [1]
4437	Heating Degree-Day	A form of the degree-day used as an index for fuel consumption. [1]
4438	Heave Compensation	The removal of the effect of wave motion from the recorded seabed profile. [14]
4439	High Water: Double	A high water consisting of two maxima of nearly the same height separated by a relatively small depression. See also tide: double. [14]
4440	Horizon Photograph	In aerial photography, a photograph of the horizon, taken simultaneously with a vertical photograph and used to determine the relative tilt between adjacent vertical photographs. [14]
4441	Horizon: Celestial	That circle of the celestial sphere, formed by the intersection of the celestial sphere and a plane through the center of the earth, and perpendicular to the zenith-nadir line. Also called rational horizon. [14]
4442	Horizontal Coplane	See coplane: basal. [14]
4443	Hydrographic Chart	See chart: nautical. [14]
4444	Hydrographic Datum	See datum: chart. [14]
4445	Hydroplastic Corer	See corer. [14]
4446	Indirect Levelling	See levelling. [14]
4447	Instrument Shelter	A boxlike (often wooden) structure designed to protect weather instruments from direct sunshine and precipitation. [1]
4448	Inverting Eyepiece	See eyepiece: erecting. [14]
4449	Isometric Latitude	See latitude. [14]
4450	Latitude: Magnetic	The angle whose tangent is one half the tangent of the magnetic inclination or dip. [14]
4451	Layer Of No Motion	A layer, assumed to be at rest at some depth in the ocean. [14]
4452	Librations Of Moon	Motions of the moon due to which certain margins round the moon's limb occasionally pass out of view while a corresponding margin on the other side comes into view. The librations enable 59 per cent of the moon's surface to be seen at one time or another. [14]
4453	Light(S): Boundary	Lights marking the boundary of a landing area. [14]
4454	Light(S): Vertical	Two or more lights disposed vertically to give a different character or appearance. [14]
4455	Light: Alternating	A signal light that shows, in any given direction, two or more colors in a regularly repeated sequence with a regular periodicity. [14]
4456	Light: Group Quick	A light in which flashes are combined in groups including the same number of quick flashes (repetition rate : 50-79 per minute) and in which groups are repeated at regular intervals. [14]
4457	Light: Obstruction	Light indicating the presence of an obstruction. [14]
4458	Lighted Sound Buoy	See buoy. [14]
4459	Longwave Radiation	A term most often used to describe the infrared energy emitted by the earth and the atmosphere. [1]
4460	Low Frequency (Lf)	See frequency: radio. [14]
4461	Low Velocity Layer	Any layer in which the velocity of compressional wave propagation is lower than in the adjacent layers. Such a layer can act as an efficient channel for the propagation of elastic waves for great distances. [14]
4462	Low-Tide Elevation	A naturally formed area of land which is surrounded by and above water at low tide, but submerged at high tide. [14]
4463	Magnetic Induction	The act or process by which material becomes magnetized when placed in a magnetic field. [14]
4464	Magnetic Variation	See variation. [14]
4465	Magnetism: Induced	Magnetism acquired by a piece of magnetic material while it is in a magnetic field. [14]
4466	Map: Hemispherical	A map of one half of the earth's surface, bounded by the equator, or by meridians. [14]
4467	Maregraph Plongeur	An instrument for measuring changes in sea level by automatically recording changes in pressure at sea bottom. Two bourdon tubes are open to pressure and a mechanism records the resultant movements of their free ends. [14]
4468	Marker Radiobeacon	See marker beacon. [14]
4469	Mathematical Model	A mathematical representation, usually of a process, device, or concept, which permits mathematical manipulation of variables as a means to determine how the process, device, or concept would behave in various situations as e.g. The application of a specific simulation. [14]
4470	Meridian Telescope	See telescope. [14]
4471	Meridian: Geodetic	A line on a spheroid which has the same geodetic longitude at every point. [14]
4472	Meridian: Magnetic	A line of horizontal magnetic force of the earth. The vertical plane in which a freely suspended, symmetrically magnetized needle, influenced by no transient, artificial, magnetic disturbance, will come to rest. [14]
4473	Meridian: Standard	The meridian used for reckoning standard time. A meridian of a map projection, along which the scale is as stated. [14]
4474	Micrometer: Run Of	See error of run. [14]
4475	Middle Ground Buoy	A buoy marking a shoal with channels on both sides. See bifurcation buoy, junction buoy. [14]
4476	Minor Control Plot	See radial triangulation. [14]
4477	Moat (Or Sea Moat)	an annular depression that may not be continuous, located at the base of many seamounts, oceanic islands and other isolated elevations. [14]
4478	Month: Anomalistic	The interval of time between two successive passages of the moon in its orbit through perigee. The length of the anomalistic month is 27.55455 mean solar days. [14]
4479	Mosaic: Controlled	A mosaic oriented and scaled to horizontal ground control; usually assembled from rectified photographs. See also orthophoto mosaic, uncontrolled mosaic. [14]
4480	Navigation: Aerial	See navigation: air. [14]
4481	Navigation: Marine	Navigation of watercraft. [14]
4482	Navigational Stars	Selected bright stars whose positions are precisely tabulated in nautical almanacs for navigational purposes. [14]
4483	Negative Engraving	A chart reproduction process in which the compilation manuscript, or other data, is photographed onto a plastic or glass negative. The art of creating facsimile images on a reproduction media by utilizing hand engraving techniques. [14]
4484	Noctilucent Clouds	Wavy, thin, bluish-white clouds that are best seen at twilight in polar latitudes. They form at altitudes about 80 to 90 km above the surface. [1]
4485	Nodal Point: Front	See nodal point. [14]
4486	Nonharmonic Method	In tide prediction, an approximate method based on the principle that 'the tide follows the moon'. It makes use of the close relationship that exists between the time of tide at most places and the moon's meridian transit. [14]
4487	Notice To Mariners	A periodical or casual notice issued by hydrographic offices, or other competent authorities, regarding changes in aids to navigation, dangers to navigation, important new soundings, and, in general, all such information as affects nautical charts, sailing directions, light lists and other nautical publications. [14]
4488	Oceanographic Cast	See cast. [14]
4489	Offset Lithography	A method of printing in which an image is transferred from a printing plate on to a rubber-surfaced blanket and thence on the paper. The image on the plate is a right reading image. [14]
4490	Orientation: Inner	See orientation: interior. [14]
4491	Orientation: Outer	See orientation: exterior. [14]
4492	Parallax: Personal	See parallax: instrumental. [14]
4493	Parallax: Vertical	See parallax: y-. [14]
4494	Parallel: Geodetic	A line on the spheroid which has the same geodetic latitude at every point. A geodetic parallel, other than the equator, is not a geodetic line. In form, it is a small circle whose plane is parallel with the plane of the geodetic equator. [14]
4495	Parallel: Standard	A parallel of latitude which is used as a control in the computation of a map projection. For a tangent cone, this is the parallel of tangency. For a secant cone, the two parallels of intersection are the standards. [14]
4496	Paraselenic Circle	Photometeor of the halo family, analogous to the parhelic circle, the luminary being the moon. [14]
4497	Particulate Matter	Solid particles or liquid droplets that are small enough to remain suspended in the air. Also called aerosols. [1]
4498	Photocontrol Point	See control point. [14]
4499	Photograph: Aerial	Any photograph taken from the air. Sometimes called air photograph. [14]
4500	Photograph: Ground	See photograph: terrestrial. [14]
4501	Platform: Offshore	A permanent offshore structure, either fixed or floating, used in the production of oil or natural gas. [14]
4502	Polar Front Theory	A theory developed by a group of Scandinavian meteorologists that explains the formation, development, and overall life history of cyclonic storms that form along the polar front. [1]
4503	Polaris Correction	A correction to be applied to the observed altitude of Polaris to obtain the latitude. [14]
4504	Polarization Error	See error. [14]
4505	Position: Adjusted	An adjusted value of the coordinate position of a point on the earth. [14]
4506	Position: Apparent	In astronomy, the position of a celestial body reduced to the center of the earth. It differs from the position in which the object is observed as to the effects of refraction, diurnal aberration, and diurnal parallax. [14]
4507	Position: Geodetic	A point on the earth, the coordinates of which have been determined by triangulation from an initial station whose location has been established as a result of astronomical observations. The coor-dinates of such a position depend upon the reference spheroid used. [14]
4508	Position: Relative	A point defined with reference to another position, either fixed or moving. [14]
4509	Precautionary Area	A routing measure comprising an area within defined limits where ships must navigate with particular caution and within which the direction of traffic flow may be recommended. [14]
4510	Principal Distance	The perpendicular distance from the internal perspective center to the plane of a particular finished negative or print. This distance is equal to the calibrated focal length corrected for both the enlargement or reduction ratio of the film or paper shrinkage or expansion and maintains the same perspective angles at the internal perspective center to points on the finished negative or print, as existing in the taking camera at the moment of exposure. [14]
4511	Principal Meridian	See meridian. [14]
4512	Projection: Skewed	Any standard projection used in map or chart construction, which does not conform to a general north-south format with relation to the neat lines of the map or chart. [14]
4513	Pulse (Or Impulse)	A variation of quantity whose value is normally constant (often zero), the variation being characterized by a rise and a decay. A common example is a very short burst of electromagnetic energy. See wave: continuous. [14]
4514	Range Of Mountains	See mountain range. [14]
4515	Rayleigh Criterion	Used in tidal analysis. Only those harmonic constituents which are separated by at least a complete period from their neighbouring constituents over the length of data available should be included in the harmonic analysis of a given time series. [14]
4516	Recommended Course	See track: recommended. [14]
4517	Reconnaissance Map	See map. [14]
4518	Rectified Altitude	See altitude: apparent. [14]
4519	Rectilinear Stream	See current: reversing. [14]
4520	Reduction Of Tides	The processing of observed tidal data to obtain mean values of tidal constants. [14]
4521	Residual Deviation	See deviation. [14]
4522	Residual Magnetism	See magnetism. [14]
4523	Rhumb Line Sailing	See sailing. [14]
4524	Route: Recommended	A route of undefined width, for the convenience of ships in transit, which is often marked by centerline buoys. [14]
4525	Rudite (Or Rudyte)	Rock or sediment deposits composed of grains larger than 2 millimeters. [14]
4526	Sailing Directions	Information published in book form describing coasts, waters, channels, harbor facilities, etc., for use by mariners. [14]
4527	Sailing: Composite	A modification of great-circle sailing used when it is desired to limit the highest latitude. [14]
4528	Sailing: Spherical	Any of the sailings which consider the spherical or spheroidal shape of the earth. [14]
4529	Satellite Sounding	Sounding effected by means of instruments placed on board an artificial satellite. [14]
4530	Scale: Logarithmic	A scale graduated in the logarithms of uniformly-spaced consecutive numbers. [14]
4531	Sea-Level Pressure	The atmospheric pressure at mean sea level. [1]
4532	Seamount (Or Peak)	An isolated or comparatively isolated elevation rising 1 000 meters or more from the sea floor and of limited extent across the summit. [14]
4533	Second Nodal Point	See nodal point. [14]
4534	Seismic Reflection	The study of the shallower internal structure of the earth by generating acoustic waves and registering their reflection from subsurface layers. [14]
4535	Seismic Refraction	The study of the shallower internal structure of the earth by generating acoustic waves and registering their return at increasing distances from the acoustic source, thus detecting waves that have been transmitted along deeper layers of greater elasticity and rigidity. [14]
4536	Sextant Adjustment	The process of checking the accuracy of a sextant and removing or reducing its error. [14]
4537	Sextant: Surveying	See sextant: sounding. [14]
4538	Small Tropic Range	See range. [14]
4539	Solsticial Tide(S)	See tide. [14]
4540	Sounding Apparatus	Any apparatus designed for use in measuring the depth of water. [14]
4541	Sounding Selection	1. Water depths numerically displayed on a chart. 2. The process of choosing individual water depths from a hydrographic survey in the compilation of a chart. [14]
4542	Sounding(S): Minus	(US Terminology). Soundings that reduce to height above the sounding datum (plane of reference) when corrected for height of tide. Minus soundings are shown on the smooth sheet preceded by a minus sign. [14]
4543	Sounding: Acoustic	See echo sounding. [14]
4544	Sounding: Doubtful	A depth shown on a chart over a shoal, a rock, etc., that may be less than that indicated. [14]
4545	Squares: Method Of	A method of transferring one survey to another of different scale. Also called squaring down or squaring up depending on whether the scale is being decreased or increased. [14]
4546	Stabilizer: Marine	A device installed on ships to reduce rolling. [14]
4547	State Of Sea Scale	Numerical scale of average wave height in which the numbers increase with the wave height. [14]
4548	Station: Eccentric	See eccentric station. [14]
4549	Station: Reference	A place where tide or tidal current constants have been determined from observations, and which is used as a standard for the comparison of simultaneous observations at a subordinate station. It is also a place for which independent daily predictions are given in the tide or tidal current tables, from which corresponding predictions are obtained for other locations by means of differences or factors. Also called standard station and standard port (British terminology). [14]
4550	Station: Resection	A station located by resection methods. [14]
4551	Station: Satellite	See eccentric station. [14]
4552	Station: Secondary	See station: supplementary. [14]
4553	Stereoscopic Model	See stereoscopic image. [14]
4554	Straight-Line Wind	Strong winds created by a thunderstorm's downdraft that flows outward, away from the storm in a straight line, more or less parallel to the ground. [1]
4555	Strength Of Figure	In geodesy, the comparative precision of computed lengths in a triangulation net as determined by the size of the angles, the number of conditions to be satisfied, and the distribution of bases and points of fixed position. [14]
4556	Sub-Sea Completion	See well: production. [14]
4557	Subsidiary Station	See station. [14]
4558	Subsurface Current	See current. [14]
4559	Superior Planet(S)	See planet(s): superior. [14]
4560	Superjacent Waters	The waters lying immediately above the sea-bed or deep ocean floor up to the surface. [14]
4561	Surface Navigation	See navigation. [14]
4562	Surface Reflection	The return of sound rays to depth after striking the sea surface. [14]
4563	Surveyor'S Compass	See compass. [14]
4564	System Development	The development of a program system comprising analysis, design, programming, testing, and implementation. [14]
4565	Telescopic Alidade	See alidade. [14]
4566	Terrestrial Camera	See camera. [14]
4567	Territorial Waters	See territorial sea. [14]
4568	Tide(S): Predicted	The expected times and heights of the tide as given in the tide tables in advance of their occurrence. [14]
4569	Tide(S): Secondary	Those additional tides higher low waters and lower high waters that occur twice a month (when the moon is over the equator) in a general pattern of diurnal tides. [14]
4570	Tide: Astronomical	Tide due to the attraction of the sun and moon, in contrast to a meteorological tide, caused by meterological conditions. Equilibrium tide. [14]
4571	Time: Geologic(Al)	The division into a number of great eras, each represented by a group of rocks. [14]
4572	Transit Theodolite	See transit. [14]
4573	Vertical Clearance	The minimum vertical space available for passage. [14]
4574	Very Open Pack Ice	Sea ice the concentration of which ranges between 1/10ths 3/10ths. [14]
4575	Visibility: Flight	The visibility forward from the cockpit of an aircraft in flight. [14]
4576	Warning: Hurricane	Meteorological message intended to warn those concerned of the occurrence or expected occurrence of a wind of beaufort force 12 over a specified area. Tropical cyclone warning relating to a hurricane. [14]
4577	Water Specimen Cup	See water bottle. [14]
4578	Wave: Longitudinal	A wave in which the direction of displacement of each particle in the medium is perpendicular to the wave front. [14]
4579	Wellhead: Offshore	See well: offshore. [14]
4580	Wire And Bar Sweep	See bar sweeping and wire drag sweep. [14]
4581	Acoustic Navigation	See navigation: sonic. [14]
4582	Altitude Difference	See intercept. [14]
4583	Altitude: Rectified	See altitude: apparent. [14]
4584	Aperture Of Antenna	The diameter of a reflector antenna, usually expressed in units of wavelength. [14]
4585	Apparent Precession	Apparent change in the direction of the axis of rotation of a spinning body, as a gyroscope, due to the rotation of the earth. [14]
4586	Archipelagic Waters	The waters enclosed by archipelagic baselines. [14]
4587	Astronomic(Al) Tide	See tide. [14]
4588	Astronomic(Al) Time	See time. [14]
4589	Astronomic(Al) Year	See year: tropical. [14]
4590	Astronomy: Geodetic	Astronomy as applied to geodesy. [14]
4591	Axis Of Collimation	See collimation axis. [14]
4592	Axis Of Perspective	See axis of homology. [14]
4593	Barometric Gradient	See pressure gradient. [14]
4594	Barometric Pressure	See pressure: barometric. [14]
4595	Base Line Extension	In radiolocation, the extension of the base line beyond the transmitters. [14]
4596	Base Tape (Or Wire)	A tape or wire of metal or alloy, so designed and graduated that it is suitable for measuring the lengths of bases. See also tape: invar, tape: steel and wire: invar. [14]
4597	Beacon: Transponder	See transponder beacon. [14]
4598	Bearing: Reciprocal	A bearing differing by 180° from a given bearing. [14]
4599	Beaufort Wind Scale	A numerical scale for indicating wind speed, devised by admiral sir francis beaufort in 1805. Beaufort numbers (or forces) range from force 0 (calm) to force 12 (hurricane). [14]
4600	Buoy: Lighted Sound	A light buoy provided with a sound signal. [14]
4601	Buoyancy: Centre Of	Centre of gravity of liquid displaced by a floating body. [14]
4602	Buoy-Control Method	A system of accurately located buoys on which three-point fixes could be observed, or to which distances could be measured by radio acoustic methods, for extending hydrographic surveys beyond the visibility of shore control. [14]
4603	Camera: Terrestrial	A camera designed for use on the ground. See phototheodolite. [14]
4604	Cardanic Suspension	See gimbals. [14]
4605	Cay (Also Kay, Key)	A low, flat island of sand, coral, etc. Awash or drying at low water; a term originally applied to the coral islets around the coast and islands of Caribbean sea. [14]
4606	Cesium Magnetometer	See magnetometer. [14]
4607	Chart: Aeronautical	A representation of a portion of the earth, its culture and relief, specifically designed to meet the requirements of air navigation. [14]
4608	Chart: Great Circle	See chart: gnomonic. [14]
4609	Chart: Hydrographic	See chart: nautical. [14]
4610	Chronometric Method	A former method of determining longitude by transporting chronometers between stations whose difference of longitude was to be determined. [14]
4611	Circle: Fundamental	See primary great circle. [14]
4612	Closing The Horizon	See horizon. [14]
4613	Coast Guard Station	a station at which a visual/radio/radar marine watch is kept either continuously or at certain times only. [14]
4614	Colour Of Sea Water	See sea water. [14]
4615	Colure: Equinoctial	The hour circle through the equinoxes. [14]
4616	Compass Calibration	See swinging ship. [14]
4617	Compass: Gyroscopic	A compass having one or more gyroscopes as the directive element, and tending to indicate true north. Also called gyro compass. [14]
4618	Compass: Surveyor'S	An instrument for determining a magnetic bearing of a line of sight by the use of a sighting device, a graduated horizontal circle and a pivoted needle. [14]
4619	Compilation Diagram	See source diagram. [14]
4620	Conical Projections	The map projections produced by projecting the geographic meridians and parallels onto a cone which is tangent to or intersects the surface of a sphere, and then developing the cone into a plane. [14]
4621	Contour: Depression	A closed contour inside of which the ground is at lower elevation than outside. See also form line. [14]
4622	Control: Horizontal	Control that is determined in horizontal position. The position may be referred to any recognized geographic or plane coordinate system. [14]
4623	Corer: Hydroplastic	A deep sea coring device, developed at the US Naval oceanographic office, to obtain 3 1/2-inch diameter cores up to 12 feet in length. The barrel is constructed of high-impact grade polyvinyl chloride plastic without an inner liner. Also called polyvinyl corer. [14]
4624	Correction(S): Tape	See tape correction(s). [14]
4625	Course: Recommended	See track: recommended. [14]
4626	Current: Subsurface	A current usually flowing below the thermocline generally at slower speeds and frequently in a different direction from the currents near the surface. [14]
4627	Day: Apparent Solar	See day: solar. [14]
4628	Delambre'S Spheroid	See reference spheroid. [14]
4629	Departure: Point Of	The point from which the initial course to reach the point of destination begins. [14]
4630	Depth: Compensation	The depth at which the light intensity is just sufficient to bring about a balance between the oxygen produced by algae through photosynthesis and that consumed by them through respiration. [14]
4631	Depth: Thermometric	The depth, in meters, at which paired protected and unprotected thermometers attached to a nansen bottle are reversed. The difference between the corrected readings of the 2 thermometers represents the effect of the hydrostatic pressure at the depth of reversal. This depth may then be determined by formula or from a depth anomaly graph. Depths obtained by this means are of greatest value when a wire angle occurs. [14]
4632	Detection Threshold	The lowest or highest level of a parameter above or below which sensing equipment can detect the parameter. [14]
4633	Deviation: Constant	Deviation which is the same on any heading, which may result from certain arrangements of asymmetrical horizontal soft iron. [14]
4634	Deviation: Magnetic	The angle between the compass needle and the magnetic meridian, expressed in degrees east or west of magnetic meridian. Also called deviation. [14]
4635	Deviation: Residual	Deviation of a magnetic compass after compensation. [14]
4636	Deviation: Standard	See error: standard. [14]
4637	Directional Antenna	See antenna. [14]
4638	Discontinuity Layer	See thermocline. [14]
4639	Displacement Drafts	See draft. [14]
4640	Distortion: Angular	In cartography, distortion in a projection because of non-conformality. See conformality. [14]
4641	Dynamic Positioning	Manoeuvring of a vessel to keep a position relative to a seabed feature; normally underwater acoustic position fixing systems are used for this purpose. [14]
4642	Eccentric Reduction	In triangulation, the correction which must be applied to a direction observed by an instrument with either the instrument or signal, or both, eccentric, to reduce the observed value to what it would have been if there had been no eccentricity. [14]
4643	Electromagnetic Log	See log. [14]
4644	Elevation: Angle Of	See angle of elevation. [14]
4645	Epact (Of The Year)	The age of the moon at 00 hour on january 1. [14]
4646	Equation: Condition	An equation which expresses exactly certain relationships that must exist among related quantities, which are not independent of one another, exist a priori, and are separate from relationships demanded by observation. [14]
4647	Equation: Correlate	An equation derived from an observation or condition equation, using undetermined multipliers, and expressing the condition that the sum of the squares of the residual errors resulting from the application of these multipliers to the observation or condition equations shall be a minimum. [14]
4648	Error Of Graduation	Inaccuracy in the graduations of the scale of an instrument. Also called graduation error. [14]
4649	Eyepiece Micrometer	See micrometer: ocular. [14]
4650	Eyewall Replacement	A situation within a hurricane (tropical cyclone) where the storm's original eyewall dissipates and a new eyewall forms outward, farther away from the center of the storm. [1]
4651	Fish Trap (Or Weir)	A structure for catching fish. See also tunny net. [14]
4652	Flare Triangulation	See triangulation. [14]
4653	Floating Breakwater	A contrivance consisting of a series of square frames of timber connected by mooring chains or cables attached to anchors or stone blocks in such a manner as to form a basin within which vessels riding to anchor may be protected from the violence of the waves. [14]
4654	Focal-Plane Shutter	See shutter. [14]
4655	Frequency: Low (Lf)	See frequency: radio. [14]
4656	Frequency: Resonant	Any frequency at which a body or system vibrates more readily. [14]
4657	Frost (Or Freezing)	Lowering of air temperature to a value equal to or less than the freezing point of water (0°c). [14]
4658	Galton'S Sun Signal	See heliostat. [14]
4659	Geocentric Latitude	See latitude. [14]
4660	Geodetic Connection	See connection. [14]
4661	Geographic(Al) Pole	See pole. [14]
4662	Geologic(Al) Survey	See survey. [14]
4663	Geostrophic Current	A current in which the balance in the horizontal components of the equations of motion is between the horizontal pressure gradient and the Coriolis force. The vertical component is in hydrostatic balance and the pressure increases with depth in proportion to the mass of water above. If pressure is mapped on a level surface (geopotential), then geostrophic flow is parallel to the isobars, with high pressure to the right (left) of the flow in the Northern (Southern) Hemisphere. For the geostrophic balance to hold, the flow must be steady, very weak, large-scale, and friction-free. [3]
4664	Gnomonic Projection	See projection. [14]
4665	Great Diurnal Range	See range: diurnal. [14]
4666	Greatest Elongation	See elongation. [14]
4667	Grid Magnetic Angle	See variation: grid. [14]
4668	Halo (Solar, Lunar)	Group of optical phenomena, in the form of rings, arcs, pillars or bright spots, produced by the refraction or reflection of light by ice crystals suspended in the atmosphere (cirriform clouds, ice fog, etc.). [14]
4669	Harbour (Or Harbor)	A natural or artificially improved body of water providing protection for vessels, and generally anchorage and docking facilities. See also port. [14]
4670	Harmonic Prediction	In tidal terminology, the method of predicting tides and tidal currents by combining the harmonic constituents into a single curve. The work was usually done mechanically by a machine designed for this purpose, called a tide predicting machine; nowadays the work is done by computers. [14]
4671	Helium Magnetometer	See magnetometer. [14]
4672	High Frequency (Hf)	See frequency: radio. [14]
4673	Horizon: Artificial	A device for indicating the horizontal, as a bubble, gyroscope, pendulum, or the flat reflecting surface of a liquid. [14]
4674	Horizon: Dip Of The	See dip. [14]
4675	Humidity Of The Air	Water vapor content of the air. [14]
4676	Hydrographic Circle	See circle. [14]
4677	Hydrophone Streamer	A chain of separate receivers for seismic sound sources towed by a ship. The streamer contains many individual hydrophone elements and is divided electronically into a number of discrete sections or channels. [14]
4678	Incidence: Angle Of	See angle of incidence. [14]
4679	Index Of Refraction	See refraction: index of. [14]
4680	Inertia: Gyroscopic	See gyroscopic inertia. [14]
4681	Inertial Navigation	See navigation. [14]
4682	Inferior Planet (S)	See planet (s): inferior. [14]
4683	Intensity: Magnetic	See magnetic field intensity. [14]
4684	Intercardinal Point	Any of the four directions midway between the cardinal points: north-east, north-west, south-east, south-west. [14]
4685	Interglacial Period	A time interval of relatively mild climate during the ice age when continental ice sheets were absent or limited in extent to greenland and the antarctic. [1]
4686	Latitude: Celestial	Angular distance north or south of the ecliptic; the arc of a circle of latitude between the ecliptic and a point on the celestial sphere, measured northward or southward from the ecliptic through 90°, and labelled n or s to indicate the direction of measurement. Also called ecliptic latitude. [14]
4687	Latitude: Geometric	See latitude: parametric. [14]
4688	Latitude: Isometric	An auxiliary latitude used in the conformal mapping of the spheroid on a sphere. [14]
4689	Levelling: Geodetic	Spirit levelling of a high order of accuracy, usually extended over large areas, to furnish accurate vertical control as a basis for the control in the vertical dimension for all surveying and mapping operations. [14]
4690	Levelling: Indirect	The determination of differences of elevation from (a) vertical angles and horizontal distances, as in trigonometric levelling; (b) comparative elevations derived from values of atmospheric pressure determined with a barometer, as in barometric levelling; and (c) elevations derived from values of the boiling point of water determined with a hypsometer, as in thermometric levelling. [14]
4691	Life Saving Station	a place where equipment for saving life at sea is maintained. Also called rescue station. [14]
4692	Light: Intermittent	See light: rhythmic. [14]
4693	Local Apparent Noon	See noon. [14]
4694	Local Sidereal Time	See time. [14]
4695	Long-Range Forecast	Generally used to describe a weather forecast that extends beyond about 8.5 days into the future. [1]
4696	Magnetism: Residual	Magnetism which remains after removal of the magnetizing force. [14]
4697	Magnetometer Survey	See survey. [14]
4698	Main Scheme Station	See station. [14]
4699	Map: Reconnaissance	The plotted result of a reconnaissance survey. [14]
4700	Master Gyro Compass	See compass. [14]
4701	Mature Thunderstorm	The second stage in the three-stage cycle of an ordinary thunderstorm. This mature stage is characterized by heavy showers, lightning, thunder, and violent vertical motions inside cumulonimbus clouds. [1]
4702	Maximum Thermometer	A thermometer with a small constriction just above the bulb. It is designed to measure the maximum air temperature. [1]
4703	Maximum Wave Height	Estimated highest wave height from the significant wave height calculated. [-]
4704	Mean Rise (Of Tide)	The height of mean high water above the chart datum. [14]
4705	Meridian: Celestial	A great circle of the celestial sphere through the celestial poles and the zenith. The expression usually refers to the upper branch. [14]
4706	Meridian: Greenwich	The astronomical meridian through the center of the transit instrument of the observatory of Greenwich, England, serving as the reference for Greenwich time, in contrast with local meridian. [14]
4707	Meridian: Principal	(US Terminology). A true north-south line (a meridian) extending both north and south of the initial point in the rectangular system of surveys. Together with the base line they constitute the axes of a system and the initial point the origin of that system. See principal line. [14]
4708	Meridian-Arc Method	A method of determining the dimensions of the ellipsoid by measuring (by triangulation) the linear distances between three points on a meridian and the angular distances between them from observed differences in their astronomical latitudes. [14]
4709	Meridional Distance	The difference of latitude between two points on a map projection's graticule converted to suitable linear units. [14]
4710	Meteorological Tide	See tide. [14]
4711	Milankovitch Theory	A theory proposed by Milutin Milankovitch in the 1930s suggesting that changes in the earth's orbit were responsible for variations in solar energy reaching the earth's surface and climatic changes. [1]
4712	Minimum Thermometer	A thermometer designed to measure the minimum air temperature during a desired time period. [1]
4713	Monsoon Wind System	A wind system that reverses direction between winter and summer. Usually the wind blows from land to sea in winter and from sea to land in summer. [1]
4714	Most Probable Value	That value of a quantity which is mathematically determined from a series of observations and is more probably free of the effects of blunders and errors than any other value that might stem from the same series of observations. [14]
4715	Multiple Tide Staff	See tide staff. [14]
4716	Navigation: Doppler	Navigation using equipment employing doppler shift measurement techniques with respect to transmitted and reflected signals to automatically compute drift angle and ground speed. Drift angle and ground speed are used in dead reckoning performed either manually or, as in many installations, by dead reckoning computers. In either case, craft heading is a necessary input. [14]
4717	Navigation: Surface	Navigation of a craft on the surface of the earth. The expression is used particularly with reference to navigation of vessels on the surface of water. See navigation: land and navigation: underwater. [14]
4718	Navigational Drafts	See draft. [14]
4719	Oceanic Circulation	A unique interrelated system of major ocean currents within a large area; usually a closed circular pattern such as in the north Atlantic, Mediterranean, etc. [14]
4720	Orange Peel Sampler	A bottom sediment sampling device capable of obtaining as much as 1/2 cubic foot of sample from the ocean floor. Named for its likeness to an orange that has its peel quartered. [14]
4721	Parallax Correction	A correction due to parallax, particularly that sextant altitude correction due to the difference between the apparent direction from a point on the surface of the earth to a celestial body and the apparent direction from the center of the earth to the same body. [14]
4722	Parallax Difference	In photogrammetry, the difference in the absolute stereoscopic parallaxes of two points imaged on a pair of photographs. Customarily used in determination of the difference in elevations of objects. [14]
4723	Parallax Inequality	The variation in the range of tide or in the speed of tidal currents due to the continual change in the distance of the moon from the earth. [14]
4724	Parallel: Celestial	See parallel of declination. [14]
4725	Parallel: Isometric	In photogrammetry, the intersecting line between the plane of a photograph and a horizontal plane having an equal perpendicular distance from the same perspective center. [14]
4726	Parallel: Principal	See parallel: photograph. [14]
4727	Personal Correction	The correction due to personal error. [14]
4728	Photoelectric Pilot	A device for automatic steering in conjunction with the magnetic compass. Its pinnacle unit, or directive element, consists of a high-grade magnetic compass of special construction, a simple light system, and a photoelectric cell, so arranged that the slightest deviation of the vessel from its course is detected and relayed to the steering engine unit. [14]
4729	Photograph: Oblique	A photograph taken with the camera axis intentionally directed between the horizontal and the vertical. [14]
4730	Photography: Aerial	The art, science, or process of taking aerial photographs. [14]
4731	Planet(S): Inferior	The planets with orbits smaller than that of the earth: mercury and venus. [14]
4732	Planet(S): Superior	The planets with orbits larger than that of the earth: mars, jupiter, saturn, uranus, neptune, and pluto. [14]
4733	Position: Estimated	The most probable position of a craft determined from incomplete data or data of questionable accuracy. Such a position might be determined by applying a correction to the dead reckoning position. [14]
4734	Precision Ephemeris	The ephemeris which describe the orbit of a navigational satellite precisely. They are of higher precision than the broadcast ephemeris but not available in real time. [14]
4735	Pressure Hydrophone	A hydrophone in which the electric output substantially corresponds to the instantaneous sound pressure of the impressed sound wave. [14]
4736	Prismatic Astrolabe	See astrolabe. [14]
4737	Production Platform	A term used to indicate a permanent offshore structure equipped to control the flow of oil or gas. For charting purposes, the use of the term is extended to include all permanent platforms associa-ted with oil or gas production, e.g., field terminal, drilling and accommodation platforms, and "booster" platforms located at intervals along some pipelines. It does not include entirely submarine structures. See also platform. [14]
4738	Projection: Cassini	A conventional projection constructed by computing the lengths of arcs along a selected geographic meridian and along a great circle perpendicular to that meridian, and plotting these as rectangular coordinates on a plane. [14]
4739	Radar Guided Tracks	Recommended tracks along which ships can be guided by coastal radar stations in the event of bad visibility. [14]
4740	Radiation Inversion	An increase in temperature with height due to radiational cooling of the earth's surface. Also called a nocturnal inversion. [1]
4741	Radiational Cooling	The process by which the earth's surface and adjacent air cool by emitting infrared radiation. [1]
4742	Radiocommunications	Any telecommunication by means of radio waves. [14]
4743	Range: Great Tropic	The difference in height between tropic higher high water and tropic lower low water. [14]
4744	Range: Small Tropic	The difference in height between tropic lower high water and tropic higher low water. [14]
4745	Recording Barometer	See barometer. [14]
4746	Recoverable Station	See station. [14]
4747	Recovery Of Station	In surveying, the identifying and checking of an original station. This is considered as recovered when its mark (monument) is identified as authentic and proved to be occupying its original site. [14]
4748	Rectilinear Current	See current: reversing. [14]
4749	Rectoblique Plotter	A mechanical device intended for rectification of individual rays on tilted or oblique photographs. [14]
4750	Reduction To Centre	The amount which must be applied to a direction observed at an eccentric station, or to an eccentric signal, to reduce such direction to what it would be if there were no such eccentricity. [14]
4751	Refraction Of Light	The bending of light rays in passing from one transparent medium into another which has a different index of refraction. [14]
4752	Refraction: Coastal	A small change in the direction of travel of a radio wave when it crosses a shoreline obliquely due to a difference in conducting and reflecting properties between land and water, and thus velocity. [14]
4753	Relief Displacement	Displacement of images radially inward or outward with respect to the photograph nadir, according as the ground objects are, respectively, below or above the elevation of the ground nadir. [14]
4754	Right Reading Image	An image which may be read or observed normally whether in negative or positive form. [14]
4755	Sailing: Rhumb Line	Any sailing when a rhumb line is involved. [14]
4756	Saturation (Of Air)	An atmospheric condition whereby the level of water vapor is the maximum possible at the existing temperature and pressure. [1]
4757	Sediment(S): Bottom	In general all sedimentary material regardless of origin found on or in the submarine bottom, including ballast or other material dumped into the sea by man. More specifically it is limited to unconsolidated mineral and organic material forming the sea bottom, not including coral reefs or bedrocks. [14]
4758	Selective Absorbers	Substances such as water vapor, carbon dioxide, clouds, and snow that absorb radiation only at particular wavelengths. [1]
4759	Semidiurnal Current	See current. [14]
4760	Sequence Of Current	The order of occurrence of the tidal current strengths of a day, with special reference to whether the greater flood immediately precedes or follows the greater ebb. [14]
4761	Serial Temperatures	The observations required to determine the vertical distribution of temperature and salinity with depth at any one place in the ocean. [14]
4762	Set Of Observations	A set of two or more observations at different settings of the apparatus made in order to eliminate certain errors which, for the apparatus concerned, are inherent in a single observation. [14]
4763	Ship Of Opportunity	An expression designating ships of commercial lines employed in gathering oceanographic data. [14]
4764	Shortwave Radiation	A term most often used to describe the radiant energy emitted from the sun, in the visible and near ultraviolet wavelengths. [1]
4765	Signal: Topographic	Any object, existing or specially erected, used for the control of topographic survey. [14]
4766	Sky-Wave Correction	The correction to be applied to the time difference reading of received sky waves to convert it to an equivalent ground wave reading. [14]
4767	Small Diurnal Range	See range. [14]
4768	Sounding: Formation	Sounding carried out by two or more ships in formation searching for a reported danger. [14]
4769	Sounding: Hand Lead	Sounding with hand lead. Hand lead soundings are usually taken from a slowly moving vessel. [14]
4770	South Magnetic Pole	See magnetic pole. [14]
4771	Special Purpose Map	See map. [14]
4772	Specular Reflection	The type of reflection, in optics or microwave theory, characteristic of a highly polished plane surface from which all rays are reflected at an angle equal to the angle of incidence. [14]
4773	Standard Rain Gauge	A nonrecording rain gauge with an 8-inch diameter collector funnel and a tube that amplifies rainfall by tenfold. [1]
4774	Station: Subsidiary	A station established to overcome some local obstacle to the progress of a survey, and not to determine position data for the station point. [14]
4775	Stereometric Camera	See camera. [14]
4776	Stereoscopic Vision	The particular application of binocular vision which enables the observer to obtain the impression of depth, usually by means of two different perspectives of an object, as two photographs taken from different air stations. [14]
4777	Stereotriangulation	A triangulation procedure that uses a stereoscopic plotting instrument to obtain the successive orientation of the stereoscopic pairs of photographs into a continuous strip. The spatial solution for the extension of horizontal and/or vertical control using these strip coordinates may be obtained by either graphical or computational procedures. Also called bridging. [14]
4778	Stream: Rectilinear	See current: reversing. [14]
4779	Strength Of Current	The phase of a tidal current at which the speed is a maximum; also the speed at this time. [14]
4780	Stripes (Of Colour)	Areas of contrasting colour separated from one another by straight lines, and used as distinguishing characteristic for navigation marks. In British terminology horizontal stripes are denoted as bands. [14]
4781	Sub-Bottom Profiler	A form of active, low frequency sonar in which acoustic beams penetrate the bottom. A recorder produces a chart which represents a cross section of the geological structure of the subbottom. See also: echo sounder. [14]
4782	Sub-Celestial Point	See sub-point. [14]
4783	Subordinate Station	See station. [14]
4784	Surface Of Position	A surface on some point of which a craft is located. [14]
4785	Survey: Exploratory	A survey executed for the purpose of obtaining general information concerning areas about which such information was not, previously, a matter of record. [14]
4786	Survey: Gravimetric	A survey made to determine the acceleration of gravity at various places on the earth's surface. [14]
4787	Survey: Large Scale	A hydrographic survey at a large scale. Large scale surveys are usually intended to furnish detailed information for dredging, or other types of harbor improvement. [14]
4788	Survey: Preliminary	See survey: reconnaissance. [14]
4789	Survey: Topographic	A survey which has for its major purpose the determination of the configuration (relief) of the surface of the earth and the location of natural and artificial objects thereon. [14]
4790	Talweg (Or Thalweg)	The line joining the lowest points of a valley throughout its length. Sometimes called valley line. [14]
4791	Telescope: Meridian	A telescope whose motion along a vertical circle is intended to lie in the plane of the meridian. [14]
4792	Telluric Current(S)	See current: telluric. [14]
4793	Temporary Magnetism	See magnetism. [14]
4794	Terrestrial Equator	See equator. [14]
4795	Theodolite: Transit	See transit. [14]
4796	Three-Point Problem	The determination of the horizontal position of a point of observation from data comprising two observed horizontal angles between three objects of known position. The problem is solved either graphically by the use of a three-arm protractor, or analytically by trigonometrical computation. [14]
4797	Tidal Current Chart	See chart. [14]
4798	Tide(S): Equatorial	Tides that occur approximately every two weeks when the moon is over the equator. At these times, the moon produces minimum diurnal inequality in the tide. [14]
4799	Tide(S): Solsticial	Tides occurring near the times of the solstices, when the tropic range is especially large. [14]
4800	Topographic Station	See station. [14]
4801	Track: Great-Circle	The track of a craft following a great circle, or a great circle which a craft intends to follow approximately. [14]
4802	Track: Radar Guided	See radar. [14]
4803	Triangulation Tower	A triangulation signal consisting of two separate structures, independent of one another an inner structure which supports the theodolite and sometimes the target or signal lamp, and an outer structure which supports the observer and his assistants and sometimes the target or signal lamp. Triangulation towers are used to elevate the line of sight above trees, topographic features, and other obstacles that might interfere with the observations. See bilby steel tower. [14]
4804	Tropic Of Capricorn	The southern parallel of declination, approximately 23°27' from the celestial equator, reached by the sun at its maximum southerly declination, or the corresponding parallel on the earth. [14]
4805	Tropical Depression	A mass of thunderstorms and clouds generally with a cyclonic wind circulation of between 20 and 34 knots. [1]
4806	Uncontrolled Mosaic	A mosaic composed of uncorrected prints, the detail of which has been matched from print to print without ground control or other orientation. [14]
4807	Underkeel Allowance	The minimum under keel clearance estimated, or specified by a relevant authority for a defined area or vessel type, to account for vessels' static and dynamic characteristics, sea state, chart reliability, and variance from predicted height of tide. [14]
4808	Underkeel Clearance	The distance between the lowest point of the ship's hull, normally some point on the keel, and the sea floor. [14]
4809	United Nations (Un)	The major international organization established to maintain international peace and security, to develop friendly relations among nations, to achieve cooperation in solving international problems. [14]
4810	Vertical Deflection	See deflection of the vertical. [14]
4811	Vertical Photograph	See photograph. [14]
4812	Very Close Pack Ice	Sea ice the concentration of which is practically 10/10ths with little if any water present. [14]
4813	Warning: Navigation	See navigational warning. [14]
4814	Wave Of Translation	A wave in which the individual particles of the medium are shifted in the direction of wave travel, as ocean waves in shoal waters. Distinguished from an oscillatory wave. [14]
4815	Wave: Compressional	A wave in an elastic medium which causes an element of the medium to change its volume without undergoing rotation. [14]
4816	Wellhead: Submerged	A submarine structure projecting some distance above the seabed and capping a temporarily abandoned or suspended oil or gas well. [14]
4817	Wind Driven Current	See current. [14]
4818	Younger-Dryas Event	A cold episode that took place about 11,000 years ago, when average temperatures dropped suddenly and portions of the northern hemisphere reverted back to glacial conditions. [1]
4819	Zenithal Projection	See projection: azimuthal. [14]
4820	Absolute Orientation	See orientation. [14]
4821	Accuracy: Repeatable	See repeatable accuracy. [14]
4822	Aerial Triangulation	See phototriangulation. [14]
4823	Angle Of Convergence	See parallactic angle. [14]
4824	Angular Acceleration	See acceleration. [14]
4825	Antenna: Directional	An antenna for transmitting or receiving signals in, or from, a given direction. [14]
4826	Anticrepuscular Rays	Bands of light extending across the sky that appear to converge toward the horizon opposite from the sun. [1]
4827	Apparent Temperature	What the air temperature ?feels like? For various combinations of air temperature and relative humidity. [1]
4828	Approximate Position	A position that is considered to be less than third-order accuracy, but is generally considered to be within 100 feet (30.5 meters) of its correct geographic location. The method of location may be an indication of the recorded accuracy. [14]
4829	Arc Of Triangulation	See triangulation: arc of. [14]
4830	Artificial Satellite	See satellite. [14]
4831	Astrolabe: Prismatic	An astrolabe consisting of a telescope in a horizontal position, with a prism and artificial horizon attached at its objective end, used for determining astronomic positions. [14]
4832	Atmosphere: Standard	Conventional reference atmosphere, chosen to represent in a simple way the approximate average condition in the vertical. [14]
4833	Automatic Tide Gauge	See gauge: tide. [14]
4834	Axis Of Spirit Level	The line tangent to the surface of a spirit level tube against which the bubble forms, at the center of the graduated scale of the level, and in the plane of the tube and its center of curvature. Also called level axis or spirit level axis. [14]
4835	Back-Door Cold Front	A cold front moving south or southwest along the atlantic seaboard of the united states. [1]
4836	Barometer: Recording	Barometer which gives a continuous graphic representation of the atmospheric pressure variations with time. [14]
4837	Barometric Altimeter	See altimeter. [14]
4838	Barometric Elevation	See elevation. [14]
4839	Barometric Levelling	See levelling. [14]
4840	Beacon: Aeronautical	An aeronautical ground light visible at all azimuths, either continuously or intermittently, to designate a particular point on the surface of the earth. A radio beacon may be coterminous with the aeronautical beacon. [14]
4841	Beneaped (Or Neaped)	Said of a vessel left aground following a spring high tide. [14]
4842	Bottom Contour Chart	A chart designed for surface and sub-surface bathymetric navigation seaward of the 100-fathom contour. Bottom configuration is portrayed by depth contours and selected soundings. [14]
4843	Bottom Relief Survey	A survey conducted to obtain information on the spatial characteristics of the sea bottom relief. [14]
4844	Broad On The Quarter	Bearing 135° relative (broad on the starboard quarter) or 225° relative (broad on the port quarter). If the bearings are approximate, the expression on the quarter should be used. See also on the quarter. [14]
4845	Camera: Stereometric	A combination of two cameras mounted with parallel optical axes on a short rigid base; used in terrestrial photogrammetry for making photographs in stereoscopic pairs. [14]
4846	Cantilever Extension	Phototriangulation from a controlled area to an area of no control. Also, the connection by relative orientation and scaling of a series of photographs in a strip to obtain strip coordinates. [14]
4847	Carbon Dioxide (Co2)	A colorless, odorless gas whose concentration is about 0.039 percent (390 ppm) in a volume of air near sea level. It is a selective absorber of infrared radiation and, consequently, it is important in the earth's atmospheric greenhouse effect. Solid co2 is called dry ice. [1]
4848	Carbon Monoxide (Co)	A colorless, odorless, toxic gas that forms during the incomplete combustion of carbon-containing fuels. [1]
4849	Celestial Navigation	See navigation. [14]
4850	Centre: Reduction To	See reduction. [14]
4851	Chart Sounding Datum	The tidal datum to which soundings and drying heights on a chart are referred. It is usually taken to correspond to a low water stage of the tide. Often shortened to chart datum, especially when it is clear that reference is not being made to a horizontal datum. [14]
4852	Chart: Tidal Current	A chart showing by arrows and numbers the average direction and speed of tidal currents at a particular part of the current cycle. [14]
4853	Chromatic Aberration	See aberration of light. [14]
4854	Circle Of Visibility	That circle surrounding an aid to navigation and in which the aid is visible. See range of visibility. [14]
4855	Circle: Hydrographic	A double-reflecting instrument intended primarily for use in hydrographic survey; enables measurement of angles up to 180°. See also sextant: sounding. [14]
4856	Cloud Classification	System of distinguishing and grouping clouds according to one or more of the following criteria: a) appearance, b) process of formation, c) common height, d) particulate composition. [14]
4857	Collimation: Line Of	The line through the optical center of the objective lens of a telescope and the center of the reticle. Also called line of sight, sight line, pointing line or aiming line of the instrument. [14]
4858	Collimator: Vertical	A telescope so mounted that its collimation axis can be made to coincide with the vertical (or direction of plumb-line). The vertical collimator serves as an optical plumb-line, and may be designed for use in placing a mark on the ground directly under an instrument or in centering an instrument directly over a mark on the ground. [14]
4859	Compass: Master Gyro	A gyroscopic compass for controlling one or several remote indicators, called gyro repeaters. [14]
4860	Composite Photograph	See photograph. [14]
4861	Connection: Geodetic	Observations on one or more stations common to the two different geodetic schemes of triangulation to be incorporated. [14]
4862	Correction: Sky-Wave	The correction to be applied to the signals received via the ionosphere to convert them to their groundwave equivalent. [14]
4863	Current(S): Telluric	Natural electric currents that flow on or near the earth's surface in large sheets. Also called earth current. [14]
4864	Current: Drift Angle	The angle between the true heading and the track of a vessel caused by the action of current. [14]
4865	Current: Geostrophic	A current existing when the horizontal pressure gradient and the coriolis force are in balance. [14]
4866	Current: Rectilinear	See current: reversing. [14]
4867	Current: Semidiurnal	The type of tidal current having two flood and two ebb periods of nearly the same duration during a tidal day. [14]
4868	Current: Wind Driven	A current formed by the force of the wind. [14]
4869	Curvature Correction	In astronomy, a correction applied to the mean of a series of observations on a star or planet to take account of the divergence of the apparent path of the star or planet from a straight line. In geodesy, the correction applied in some geodetic work to take account of the divergence of the surface of the earth (spheroid) from a plane. [14]
4870	Danger To Navigation	Any feature or condition that might hinder, obstruct, endanger or otherwise constitute danger to safe navigation. [14]
4871	Daylight Saving Time	See time. [14]
4872	Deep Sea Thermometer	See thermometer. [14]
4873	Depression: Angle Of	See angle of depression. [14]
4874	Dip Of A Sea Horizon	The vertical angle, at the eye of an observer, between the horizontal and the line of sight to the sea horizon. [14]
4875	Direction Theodolite	See theodolite. [14]
4876	Distortion Of Medium	Changes in the dimensions of surveys or charts due to expansion or contraction of the paper on which the survey or chart is drawn or printed. See also differential shrinkage. [14]
4877	Drag (Of Theodolite)	A slight movement of the graduated circle produced by the rotation of the alidade. [14]
4878	Dry Bulb Thermometer	See thermometer. [14]
4879	Electronic Telemeter	See telemeter. [14]
4880	Emergent Nodal Point	See nodal point. [14]
4881	Ensemble Forecasting	A forecasting technique that entails running several forecast models each beginning with slightly different weather information. The forecaster's level of confidence is based on how well the models agree (or disagree) at the end of some specified time. [1]
4882	Equator: Terrestrial	A great circle of the earth in the plane of the celestial equator, and equidistant from the two poles. [14]
4883	Equilibrium Argument	The theoretical phase of a constituent of the equilibrium tide. [14]
4884	Error Of Collimation	The angle between the line of collimation (line of sight) of a telescope and its collimation axis; i.e., the angle by which the line of sight of an optical instrument differs from what it should be. Also called collimation error. [14]
4885	Ex-Meridian Altitude	See altitude. [14]
4886	Exploration Drilling	Drilling operations aimed at the exploration of resources. [14]
4887	Explosive Fog Signal	See fog signal. [14]
4888	Exterior Orientation	See orientation. [14]
4889	First Point Of Aries	See equinox. [14]
4890	First Point Of Libra	See equinox. [14]
4891	Fixed Angle Sounding	See sounding. [14]
4892	Frequency Modulation	See modulation. [14]
4893	Frequency: High (Hf)	See frequency: radio. [14]
4894	Fusion: Stereoscopic	See stereoscopic fusion. [14]
4895	Geodetic Coordinates	See coordinates. [14]
4896	Geographic(Al) Range	See range. [14]
4897	Graticule Adjustment	The transportation or movement of the graticule in order to change the origin of reference. [14]
4898	Greenwich Civil Time	See time: Greenwich mean. [14]
4899	Greenwich Hour Angle	See hour angle. [14]
4900	Ground Control Point	See control point. [14]
4901	Height Of Cloud Base	Height above the earth's surface, at a given point, of the base of the lowest cloud whose cloud amount exceeds a given value. Called ceiling in US Terminology. [14]
4902	Horizon: Closing The	Measuring the last of a series of horizontal angles at a station required to make the series complete around the horizon. See also error of closure of horizon. [14]
4903	Hydrographic Sextant	See sextant: sounding. [14]
4904	Hyperbolic Number(S)	Numerical figures characterizing the hyperbolae of a pattern or lattice in a hyperbolic system of radiolocation. [14]
4905	Incident Nodal Point	See nodal point. [14]
4906	Inshore Traffic Zone	a routing measure comprising a designated area between the landward boundary of a traffic separation scheme and the adjacent coast, to be used in accordance with the provisions of rule 10(d), as amended, of the international regulations for preventing collisions at sea , 1972 (collision regulations). [14]
4907	Intensity Of Gravity	See gravity. [14]
4908	International Waters	A nonlegal term that refers to those waters subject to the high seas freedom of navigation and overflight, i.e., contiguous zone, eez, and high seas. [14]
4909	Isobaric Chart (Map)	A chart showing variables, such as temperature and wind, on a constant-pressure surface. Variations in height are usually shown by lines of equal height (contour lines). See constant-pressure chart. [1]
4910	Isolated Danger Mark	in the IALA maritime buoyage system a navigation mark erected on, moored over, or placed immediately adjacent to an isolated danger of limited extent, which has navigable water all around it. [14]
4911	Latitude: Parametric	The angle at the center of a sphere which is tangent to the spheroid along the geodetic equator, between the plane of the equator and the radius to the point intersected on the sphere by a straight line perpendicular to the plane of the equator and passing through the point on the spheroid whose parametric latitude is defined. Parametric latitude is an auxiliary latitude used in problems of geodesy and cartography. Also called reduced latitude, geometric latitude or eccentric angle. [14]
4912	Left-Right Indicator	An instrument indicating the orthogonal distance of a position from a pre-defined track. [14]
4913	Level: Self Aligning	See levelling instrument: self-aligning level. [14]
4914	Light: Long-Flashing	A flashing light in which a single flash of not less than two seconds duration is regularly repeated. [14]
4915	Line Of Delimitation	A line drawn on a map or chart depicting the separation of any type of maritime jurisdiction. [14]
4916	Line Of Equidistance	See median line. [14]
4917	Log: Electromagnetic	A log consisting of a pulsating magnet mounted on a probe pointing downwards with two contacts on the sides of the probe. The movement of the water through the magnetic field is reflected by the contacts and the ripple of voltage thus induced can be converted to measure the speed of the craft. [14]
4918	Longitude: Celestial	Angular distance east of the vernal equinox, along the ecliptic; the arc of the ecliptic or the angle at the ecliptic pole between the circle of latitude of the vernal equinox and the circle of latitude of a point on the celestial sphere, measured eastward from the circle of latitude of the vernal equinox, through 360°. [14]
4919	Low Water Inequality	See diurnal inequality. [14]
4920	Lunicurrent Interval	The interval between the moon's transit (upper or lower) over the local or Greenwich meridian and a specified phase of the tidal current following the transit. Examples are strength of flood interval and strength of ebb interval, which may be abbreviated to flood interval and ebb interval, re-spectively. The interval is described as local or Greenwich according to whether the reference is to the moon's transit over the local or Greenwich meridian. When not otherwise specified, the reference is assumed to be local. [14]
4921	Magnetic Compensator	See compensator. [14]
4922	Magnetic Declination	See variation. [14]
4923	Magnetic Inclination	See dip. [14]
4924	Magnetism: Transient	See magnetism: temporary. [14]
4925	Magnetometer: Cesium	An optical pumping magnetometer which employs a cesium absorption cell. [14]
4926	Magnetometer: Helium	An optical pumping magnetometer which employs a helium absorption cell. [14]
4927	Map: Special Purpose	Any map designed primarily to meet specific requirements. [14]
4928	Maritime Meteorology	Branch of the meteorology which is concerned with the interaction between the sea and atmosphere. [14]
4929	Mean Range (Of Tide)	The difference in the height between mean high water and mean low water. [14]
4930	Mercator: Transverse	See projection: transverse Mercator. [14]
4931	Meridian: Photograph	In photogrammetry, the image on a photograph of any horizontal line in the object space which is parallel to the principal plane. Since all such lines meet at infinity, the image of the meeting point is at the intersection of the principal line and the horizon trace, and all photograph meridians pass through that point. [14]
4932	Mid-Holocene Maximum	A warm period in geologic history about 5000 to 6000 years ago that favored the development of plants. [1]
4933	Modulation: Sideband	A particular kind of amplitude modulation in which one of the two frequency bands on both sides of the carrier (and possibly the carrier itself) is suppressed, allowing a considerable reduction of the spectral width of the signal. [14]
4934	Multiple Sea Sampler	An instrument which comprises six water bottles arranged so that they trip and take water samples at different selected depths from a vessel under way. [14]
4935	Navigable Semicircle	See dangerous semicircle. [14]
4936	Navigation: Acoustic	See navigation: sonic. [14]
4937	Navigation: Inertial	Dead reckoning performed automatically by a device which gives a continuous indication of position by double integration of acceleration since leaving a starting point. [14]
4938	Navigation: Offshore	Navigation at distance from a coast, in contrast with coastwise navigation. [14]
4939	New Print (Of Chart)	In US Terminology, a new issue of a chart embodying only minor corrections. Such corrections are applied to the negatives and a new printing plate made. New prints do not render previous printings of the current edition obsolete. [14]
4940	Noon: Local Apparent	Twelve o'clock local apparent time. Sometimes called high noon. [14]
4941	North Celestial Pole	See pole: celestial. [14]
4942	Observation Equation	See equation. [14]
4943	Ocean Remote Sensing	A kind of remote sensing especially for conducting investigations and surveys of the ocean and the sea. [14]
4944	One-Way Traffic Lane	See traffic lane. [14]
4945	Parallax In Altitude	Geocentric parallax of a body at any altitude. The expression is used to distinguish the parallax at the given altitude from the horizontal parallax when the body is in the horizon. [14]
4946	Parallax: Geocentric	See parallax: diurnal. [14]
4947	Parallax: Horizontal	In astronomy, the geocentric parallax of a body on the observer's horizon. In photogrammetry, parallax: absolute stereoscopic. [14]
4948	Parallel Of Altitude	See almucantar. [14]
4949	Parallel: Photograph	In photogrammetry, the image on a photograph of any horizontal line in the object space which is perpendicular to the principal plane. All photograph parallels are perpendicular to the principal line. The photograph parallel passing through the principal point is the principal parallel and that passing through the isocenter is the isometric parallel. [14]
4950	Peninsula: Submarine	An elevated portion of the submarine relief resembling a peninsula. The opposite is sac. [14]
4951	Peripheral Equipment	In computer systems, any unit of equipment, distinct from the central unit, which may provide the system with outside communication. [14]
4952	Persistence Forecast	A forecast that the future weather condition will be the same as the present condition. [1]
4953	Phase(S) Of The Moon	The various appearances of the moon during different parts of the synodical month. The cycle begins with new moon or change of the moon at conjunction. The visible part of the waxing moon increases in size during the first half of the cycle until full moon appears at opposition, after which the visible part of the waning moon decreases for the remainder of the cycle. First quarter occurs when the waxing moon is at east quadrature, last quarter when the waning moon is at west quadrature. From last quarter to new and from new to first quarter the moon is crescent; from first quarter to full and from full to last quarter it is gibbous. [14]
4954	Photograph: Vertical	An aerial photograph made with the camera axis vertical (or as nearly vertical as practicable in an aircraft). [14]
4955	Piezoelectric Effect	The phenomenon, exhibited by certain crystals, in which mechanical compression produces a potential difference between opposite crystal faces, or, an applied electric field produces corresponding changes in dimensions. [14]
4956	Point Of Destination	See destination: point of. [14]
4957	Polar Tundra Climate	A climate characterized by extremely cold winters and cool summers, as the average temperature of the warmest month climbs above freezing but remains below 10°c (50°f). [1]
4958	Pole: Geographic(Al)	Either of the two points of intersection of the surface of the earth with its axis, labelled n or s to indicate either the north geographical pole or the south geographical pole. [14]
4959	Polyconic Projection	See projection. [14]
4960	Position Approximate	Of inexact position. The expression is used principally on charts to indicate that the position of a wreck, shoal, etc., has not been accurately determined or does not remain fixed. Usually shown by the abbreviation 'pa'. [14]
4961	Pressure: Barometric	Atmospheric pressure as indicated by a barometer. [14]
4962	Primary Tide Station	See station: tide. [14]
4963	Probability Forecast	A forecast of the probability of occurrence of one or more of a mutually exclusive set of weather conditions. [1]
4964	Programming Language	A language used to prepare computer programs, for example Fortran, Pascal and many others. [14]
4965	Projection: Gnomonic	A perspective projection on a plane tangent to the surface of a sphere having the point of projection at the center of the sphere. The projection is neither conformal nor equal area. It is the only projection on which great circles on the sphere are represented as straight lines. For this reason this projection is used principally for charts for great circle sailing. [14]
4966	Projection: Mercator	A conformal projection of the cylindrical type. The equator is represented by a straight line true to scale; the geographic meridians are represented by parallel straight lines perpendicular to the line representing the equator; they are spaced according to their distance apart at the equator. The geographic parallels are represented by a second system of straight lines perpendicular to the family of lines representing the meridians, and therefore parallel with the equator. Conformality is achie-ved by mathematical analysis, the spacing of the parallels being increased with the increasing distance from the equator to conform with the expanding scale along the parallels resulting from the meridians being represented by parallel lines. Since rhumb lines appear as straight lines and directions can be measured directly, this projection is widely used in navigation. [14]
4967	Projection: Zenithal	See projection: azimuthal. [14]
4968	Quarantine Anchorage	An area where a vessel anchors when satisfying quarantine regulations. [14]
4969	Radius Of Visibility	See under visibility. [14]
4970	Range: Small Diurnal	The difference in height between mean lower high water and mean higher low water. [14]
4971	Reciprocal Levelling	See levelling. [14]
4972	Recording Anemometer	See anemograph. [14]
4973	Reflecting Projector	See projector. [14]
4974	Reflecting Telescope	See telescope. [14]
4975	Reflection: Angle Of	See angle of reflection. [14]
4976	Refracting Telescope	See telescope. [14]
4977	Refraction: Index Of	The ratio of the sine of the angle of incidence to the sine of the angle of refraction. [14]
4978	Relative Orientation	See orientation. [14]
4979	Repeating Theodolite	See theodolite. [14]
4980	Reprint (Of A Chart)	(US Terminology). An issue of a chart the supply of which is approaching exhaustion. The reprint is an exact duplicate of the current issue with no changes in printing or publication data. [14]
4981	Resource Exploration	The search for economic deposits of minerals, ore, gas, oil or coal. [14]
4982	Saffir-Simpson Scale	A scale relating a hurricane's winds to the possible damage it is capable of inflicting. It is now called the saffir-simpson hurricane wind scale. [1]
4983	Sea (Or Lake) Breeze	Wind of coastal regions, blowing by day from a large water surface (sea or lake) towards the land as a result of diurnal heating of the land surface. [14]
4984	Sea Water: Colour Of	The apparent colour of the surface layers of the sea caused by the reflection of certain components of the visible light spectrum coupled with the effects of dissolved material, concentration of plankton, detritus, or other matter. Colour of oceanic water varies from deep blue to yellow and is expressed by number values which are a variation of the forel scale. Plankton concentrations may cause a temporary appearance of red, white, green, or other colors. Also called water colour. See also discoloured water. [14]
4985	Seabed Texture Chart	A tracing showing the nature and texture of the bottom, depth contours and seabed features including wrecks and obstructions. Also called bottom texture tracing. [14]
4986	Sensible Temperature	The sensation of temperature that the human body feels in contrast to the actual temperature of the environment as measured with a thermometer. [1]
4987	Short-Range Forecast	Generally used to describe a weather forecast that extends from about 6 hours to a few days into the future. [1]
4988	Shutter: Focal-Plane	A shutter located near the focal plane; usually consisting of a curtain with a slot which is pulled across the focal plane to make the exposure. [14]
4989	Sidereal Chronometer	See chronometer. [14]
4990	Signal: Hydrographic	Any object, existing or specially erected, for the control of hydrographic survey. See also sounding mark. [14]
4991	Snow Squall (Shower)	An intermittent heavy shower of snow that greatly reduces visibility. [1]
4992	Snow-Albedo Feedback	A positive feedback whereby increasing surface air temperatures enhance the melting of snow and ice in polar latitudes. This reduces the earth's albedo and allows more sunlight to reach the surface, which causes the air temperature to rise even more. [1]
4993	South Celestial Pole	See pole: celestial. [14]
4994	Spectral Peak Period	Period of the maximum (peak) energy density in the spectrum. NOTE In practice there is often more than one peak in a spectrum. [15]
4995	Speed Of Propagation	The speed with which waves of energy travel through or along a medium other than a specially constructed path. [14]
4996	Spherical Aberration	See aberration of light. [14]
4997	Station: Main Scheme	A station through which the main computations and adjustments of the survey data are carried and serve for the continued extension of the survey. [14]
4998	Station: Recoverable	A station artificially marked by well defined natural or artificial objects, whose geographic position has been accurately determined and which has been described. [14]
4999	Station: Subordinate	One of the places for which tide or tidal current predictions are determined by applying a correction to the predictions of a reference station. A tide or tidal current station at which a short series of observations was made and reduced by comparison with simultaneous observations at a reference station. Called secondary port in British terminology. See station: tide. [14]
5000	Station: Topographic	A definite point on the earth, whose geographic position has been determined by graphic methods, usually by plane table traverse or graphic triangulation. Also a point located by geodetic methods but with less than third-order accuracy. [14]
5001	Statistical Forecast	A forecast based on a mathematical/statistical examination of data that represents the past observed behavior of the forecasted weather element. [1]
5002	Stereophotogrammetry	Photogrammetry utilizing stereoscopic equipment and methods. [14]
5003	Subsidence Inversion	A temperature inversion produced by compressional warming the adiabatic warming of a layer of sinking air. [1]
5004	Sulfur Dioxide (So2)	A colorless gas that forms primarily in the burning of sulfur-containing fossil fuels. [1]
5005	Superior Conjunction	See conjunction. [14]
5006	Supplemental Control	See control. [14]
5007	Survey: Geologic(Al)	A survey or investigation of the character and structure of the earth, of the physical changes which the earth's crust has undergone or is undergoing, and of the causes producing those changes. [14]
5008	Survey: Hydrographic	A survey having for its principal purpose the determination of data relating to bodies of water. A hydrographic survey may consist of the determination of one or several of the following classes of data: depth of water; configuration and nature of the bottom; directions and force of currents; heights and times of tides and water stages; and location of topographic features and fixed objects for survey and navigation purposes. [14]
5009	Survey: Magnetometer	A survey wherein the earth's magnetic field is mapped by the use of a magnetometer. [14]
5010	Sustained Wind Speed	Time-averaged wind speed with an averaging duration of 10 min or longer. [15]
5011	Synoptic Meteorology	Branch of meteorology which is concerned with the study of meteorological elements in space. It is based on the analysis of the synoptic charts on which are plotted synoptic observations for the purpose of the weather analysis or weather forecast. [14]
5012	Synoptic Observation	Meteorological observation made at the same time (synoptic hour) at numerous stations to obtain general representation of the state of the atmosphere at the given time. [14]
5013	Terrestrial Latitude	See latitude. [14]
5014	Thermal Circulations	Air flow resulting primarily from the heating and cooling of air. [1]
5015	Thermometer: Maximum	Thermometer used for measuring the highest temperature attained during a given interval of time, for example, a day. [14]
5016	Thermometer: Minimum	Thermometer used for measuring the lowest temperature attained during a given interval of time, for example, a day. [14]
5017	Tidal Current Signal	See signal. [14]
5018	Tide Staff: Multiple	A succession of tide staffs on a sloping shore, so placed that the vertical graduations on the several staffs form a continuous scale with reference to the same datum. [14]
5019	Tide: Meteorological	A change in water level caused by local meteorological conditions, in contrast to an astronomical tide caused by the attraction of the sun and moon. [14]
5020	Tides: Mixed Diurnal	Diurnal tides which become semidiurnal with a considerable decrease of range when the moon's declination is small. [14]
5021	Time: Apparent Solar	Time measured by the apparent diurnal motion of the (true) sun. Also called true solar time, and often apparent time. [14]
5022	Time: Astronomic(Al)	Solar time in a day (astronomical day) that begins at noon. [14]
5023	Time: Local Apparent	The apparent solar time for the meridian of the observer. [14]
5024	Time: Local Sidereal	The sidereal time for the meridian of the observer. [14]
5025	Trade Wind Inversion	A temperature inversion frequently found in the subtropics over the eastern portions of the tropical oceans. [1]
5026	Transforming Printer	A specially designed projection printer of fixed geometry used for transforming the oblique components of a coupled camera installation, a multiple-lens camera, or a panoramic camera onto a plane perpendicular to the axis of the system. [14]
5027	Transit Magnetometer	See magnetometer. [14]
5028	Triangulation Signal	See signal. [14]
5029	Triangulation: Flare	A method of triangulation in which simultaneous observations are made on parachute flares. This method is used for extending triangulation over lines too long to be observed by ordinary methods. [14]
5030	Underwater Acoustics	A special field of technical acoustics dealing with the physics of sound propagation in the water. [14]
5031	Wet-Bulb Temperature	The lowest temperature that can be obtained by evaporating water into the air. [1]
5032	Wet-Bulb Thermometer	See thermometer. [14]
5033	Wire Angle Indicator	A device used to measure the angle of the sounding wire, or the oceanographic wire, from the vertical. It consists of a protractor with a weighted plumb arm. The indicator is suspended from the wire at two points and the plumb arm points to the wire angle. Also called inclinometer. [14]
5034	Acceleration: Angular	The rate of change of angular velocity. [14]
5035	Actual Vapor Pressure	The pressure exerted by the water vapor molecules in a given volume of air. Also see vapor pressure. [1]
5036	Aerial Photogrammetry	See photogrammetry. [14]
5037	Altimeter: Barometric	A sensitive aneroid barometer calibrated to read the height above a pressure datum according to the standard atmospheric pressure-to-height relationship. [14]
5038	Archipelagic Sea Lane	Sea lanes designated by an archipelagic state for the passage of ships and aircraft. [14]
5039	Automated Cartography	The performance of cartographic functions in a fully automatic mode. [14]
5040	Bearing: Great Circle	The initial direction of a great circle through two terrestrial points, expressed as angular distance from a reference direction. Bearings obtained by any form of radiant energy are great-circle bearings. [14]
5041	Calling The Soundings	Announcement made by leadsman when heaving the lead. [14]
5042	Camera: Multiple Lens	A camera with two or more lenses, with the axes of the lenses systematically arranged at fixed angles in order to cover a wide field by simultaneous exposures in all chambers. [14]
5043	Chart Amendment Patch	See chartlet. [14]
5044	Chart Comparison Unit	A device which provides simultaneous, superimposed views of a chart and radar scope. [14]
5045	Chronometer: Sidereal	A chronometer that indicates sidereal time at a given place, or that corresponding to a given meridian. [14]
5046	Chronometer: Standard	The chronometer with which the others aboard a vessel are compared and to which all observations involving time are referred. [14]
5047	Circle Of Declination	See hour circle. [14]
5048	Circle Of Uncertainty	A circle having as its center a position, however determined, and as its radius the maximum probable error of the position; a circle within which a craft is considered to be located. [14]
5049	Compensator: Magnetic	A magnet, piece of soft iron such as a sphere or iron bar, placed in a binnacle or in vicinity of a magnetic compass for reducing magnetic deviation to a minimum. Also called compass corrector or corrector magnet. See flinders bar, heeling magnet, quadrantal correctors. [14]
5050	Conjunction: Inferior	The conjunction of an inferior planet and the sun when the planet is between the earth and the sun. [14]
5051	Conjunction: Superior	The conjunction of an inferior planet and the sun when the sun is between the earth and the planet. [14]
5052	Consolidated Pack Ice	Pack ice in which the concentration is 10/10 (8/8) and the floes are frozen together. [14]
5053	Control: Astronomical	Control determined from astronomical observations. [14]
5054	Control: Supplemental	Points established by subordinate surveys, to relate aerial photographs used in mapping with the system of geodetic control. The points must be positively photo-identified, that is, the points on the ground must be positively correlated with their images on the photographs. [14]
5055	Coordinates: Geodetic	Quantities which define the horizontal position of a point on the spheroid of reference with respect to the planes of geodetic equator and of a selected geodetic meridian. See latitude: geodetic and longitude: geodetic. [14]
5056	Coring (Or Core) Tube	See core barrel. [14]
5057	Dead Reckoning Tracer	A device that automatically provides a graphical record of the dead reckoning track. See course recorder. [14]
5058	Declination: Magnetic	See variation. [14]
5059	Deviation: Quadrantal	Deviation which changes its sign (e or w) approximately each 90° change of heading. It is caused by induced magnetism in horizontal soft iron. [14]
5060	Directional Gyroscope	See gyroscope. [14]
5061	Dispersion (Of Light)	The separation of white light into its different component wavelengths. [1]
5062	Elevation: Barometric	An elevation determined with a barometer. [14]
5063	Equal Area Projection	See projection. [14]
5064	Equation: Observation	A condition equation which connects interrelated unknowns by means of an observed function. [14]
5065	Equator: Astronomical	A line connecting points having 0° astronomical latitude. [14]
5066	Equipotential Surface	A surface having the same potential of gravity at every point. [14]
5067	Equivalent Projection	See projection: equal area. [14]
5068	First Point Of Cancer	See solstice. [14]
5069	Fog Signal: Explosive	Detonation of an explosive used as a navigational warning during low visibility. [14]
5070	Gravity Anomaly Chart	See chart. [14]
5071	Gravity: Direction Of	The direction indicated by a plumb line. It is perpendicular to the surface of the geoid. Also called direction of the force of gravity. [14]
5072	Gravity: Intensity Of	The magnitude with which gravity acts, expressed in suitable units, usually as an acceleration, in gals; as a force, in dynes. [14]
5073	Great Circle: Primary	See primary great circle. [14]
5074	Heliocentric Parallax	See parallax: annual. [14]
5075	High Water Inequality	See diurnal inequality. [14]
5076	Horizontal Photograph	See photograph. [14]
5077	Hydrostatic Levelling	The transfer of level between two points by the use of a pipe filled with water laid on the sea bed with vertical sections at each end. [14]
5078	Hydrostatic Stability	See stability: static. [14]
5079	Identification Beacon	See beacon. [14]
5080	Impersonal Micrometer	See micrometer: transit. [14]
5081	Inclination: Magnetic	See dip. [14]
5082	Katabatic (Fall) Wind	Any wind blowing downslope. It is usually cold. [1]
5083	Latitude: Terrestrial	Angular distance from the equator, measured northward or southward through 90° and labelled n or s to indicate the direction of measurement. [14]
5084	Levelling: Barometric	A method of determining differences of elevation from differences of atmospheric pressure observed with a barometer. [14]
5085	Levelling: Reciprocal	Trigonometric levelling wherein vertical angles have been observed at both ends of the line to eliminate errors. [14]
5086	Light: Equal-Interval	A light with all durations of light and darkness equal. The term 'equal-interval light' has been replaced byisophase light in many countries. [14]
5087	Light: Group-Flashing	A flashing light in which a group of two or more flashes, which are specified in number, is regularly repeated. [14]
5088	Light: Quick-Flashing	A light exhibiting without interruption very rapid regular alternations of light and darkness. [14]
5089	Light: Short-Flashing	A flashing light having individual flashes of less than two seconds duration. [14]
5090	Lithographic Transfer	A proof of design or type matter pulled with special transfer ink on transfer paper from a lithographic image or a relief image. Such proofs are used to transfer an image to the plate or stone. [14]
5091	Love Wave (Or Q-Wave)	See wave. [14]
5092	Magnetometer: Transit	An instrument used primarily for observing the declination of the earth's magnetic field. [14]
5093	Marine Nature Reserve	(US Marine sanctuary). An officially designated area in which there may be restrictions on entry, fishing, anchoring, and other activities in order to protect the marine environment. [14]
5094	Medium Frequency (Mf)	See frequency: radio. [14]
5095	Medium-Range Forecast	Generally used to describe a weather forecast that extends from about 3 to 8.5 days into the future. [1]
5096	Meridian: Terrestrial	See meridian: astronomical. [14]
5097	Meridional Difference	The difference between the meridional parts of any two given parallels. [14]
5098	Modulation: Amplitude	The process of changing the amplitude of a carrier wave in accordance with the variations of a modulating wave. [14]
5099	Modulation: Frequency	Angle modulation of a sine-wave carrier in which the instantaneous frequency of the modulated wave differs from the carrier frequency by an amount proportional to the instantaneous value of the modulating wave. [14]
5100	Multispectral Imagery	Images obtained simultaneously in a number of discrete bands in the electromagnetic spectrum. [14]
5101	Multispectral Scanner	A remote-sensing device which is capable of recording data in the ultraviolet and visible portions of the electromagnetic spectrum, as well as the infrared. [14]
5102	Navigation: Celestial	Navigation with the aid of celestial bodies. Also called astro-navigation. [14]
5103	Navigation: Coastwise	Navigation in the vicinity of a coast, in contrast with offshore navigation. [14]
5104	Navigation: Submarine	Navigation of a submarine, whether submerged or surfaced. [14]
5105	No-Bottom Sounding(S)	See sounding. [14]
5106	Nodal Point: Emergent	See nodal point. [14]
5107	Nodal Point: Incident	See nodal point. [14]
5108	Nonharmonic Constants	Tidal or tidal current constants such as lunitidal intervals, ranges, and inequalities, which can be derived directly from observation without regard to the harmonic constituents. [14]
5109	Observation(S): Tidal	A series of measurements taken in order to provide the information required for the reduction of soundings, and the data for tidal prediction and investigation. [14]
5110	Oceanographic Section	A successive series of oceanographic stations carried out in a specified direction. [14]
5111	Oceanographic Station	See station. [14]
5112	Omnidirectional Range	See omnirange. [14]
5113	Orientation: Absolute	In photogrammetry, the scaling, levelling, and orientation to ground control (in a photogrammetric instrument) of a relatively oriented stereoscopic model or group of models. [14]
5114	Orientation: Exterior	In photogrammetry, the determining (analytically or in a photogrammetric instrument) of the position of the camera station and the attitude of the taking camera at the instant of exposure. In stereoscopic instrument practice, exterior orientation is divided into two parts, relative and absolute orientation. Also called outer orientation. [14]
5115	Orientation: Relative	In photogrammetry, the determining (analytically or in a photogrammetric instrument) of the position and attitude of one of a pair of overlapping photographs with respect to the other photograph. [14]
5116	Origin Of Coordinates	See coordinates: origin of. [14]
5117	Photograph: Composite	In aerial photography, a photograph made by assembling the separate photographs, made by the several lenses of a multiple lens camera in simultaneous exposure, into the equivalent of a photo-graph taken with a single wide-angle lens. [14]
5118	Picture Control Point	See control point. [14]
5119	Polar Ice Cap Climate	A climate characterized by extreme cold, as every month has an average temperature below freezing. [1]
5120	Potential Temperature	In oceanography, the temperature that a water sample would attain if raised adiabatically to the sea surface. For the deepest points of the ocean, which are just over 10 000 meters, the adiabatic cooling would be less than 1.5° c. [14]
5121	Pressure: Atmospheric	Pressure (force per unit area) exerted by the atmosphere, on any surface, by virtue of its weight: it is numerically equal to the weight of a vertical column of air above the surface of unit base area, extending to the outer limit of the atmosphere. [14]
5122	Pressure: Hydrostatic	The pressure at a given depth due to the weight of the water column above that depth. [14]
5123	Prime Vertical Circle	The vertical circle through the east and west points of the horizon. Often shortened to prime vertical. [14]
5124	Projection: Geometric	See projection: perspective. [14]
5125	Projection: Polyconic	A projection having the central geographic meridian represented by a straight line, along which the spacing for lines representing the geographic parallels is proportional to the distances apart of the parallels; the parallels are represented by arcs of circles which are not concentric, but whose centers lie on the line representing the central meridian, and whose radii are determined by the lengths of the elements of cones which are tangent along the parallels. All meridians except the central one are curved. This projection is neither conformal nor equal area but it has been widely used for maps of small areas because of the ease with which it can be constructed. [14]
5126	Projector: Reflecting	In photogrammetry, an instrument by means of which the image of an aerial photograph can be projected onto a map. By varying the position of the projector lens, the scale of the projected image can be varied, and, by tilting the table top, compensation can be made for any tilt in the photograph. [14]
5127	Proportional Dividers	An instrument consisting in its simple form of two legs pointed at both ends and provided with an adjustable pivot, so that for any given pivot setting, the distance between one set of pointed ends always bears the same ratio to the distance between the other set. A change in the pivot changes the ratio. The dividers are used in transferring measurements between charts or other drawings which are not at the same scale. [14]
5128	Protractor: Three Arm	An instrument consisting essentially of a circle graduated in degrees, to which is attached one fixed arm and two arms pivoted at the center and provided with clamps so that they can be set at any angle to the fixed arm, within the limits of the instrument. It is used for finding a ship's position, when the angles between three fixed and known points are measured. In British terminology, a perspex (or transparent plastic) device used when the marks are too close for the use of a station pointer. This instrument has replaced the cust protractor. [14]
5129	Pulse Radio Altimeter	See altimeter: radio. [14]
5130	Pulse Repetition Rate	The rate at which recurrent pulses are transmitted, usually expressed in pulses per second. [14]
5131	Punch Register System	System involving the use of prepunched holes in the flat and plate and a set of plastic pins or buttons which are used in registering succeeding flats, positioning the image on the plate, and positioning the plate on the press. See also registration. [14]
5132	Quality Of The Bottom	See bottom: nature of. [14]
5133	Range: Geographic(Al)	The greatest distance at which a light can be seen as a function of the curvature of the earth and the heights of the light source and the observer. [14]
5134	Reconnaissance Survey	See survey. [14]
5135	Refraction Correction	A correction due to refraction, particularly such a correction to a sextant altitude, due to atmospheric refraction. [14]
5136	Retentivity: Magnetic	See magnetic retentivity. [14]
5137	Reticle (Or Reticule)	A system of wires, hairs, threads, etched lines, or the like, placed normal to the axis of a telescope at its principal focus, by means of which the telescope is sighted on a star, signal, or target, or by means of which appropriate readings are made on some scale, such as a levelling or stadia rod. See also cross wires, graticule, diaphragm. In photogrammetry, a mark such as a cross or system of lines lying in the image plane of a viewing apparatus and used singly as a reference mark in certain types of monocular instruments or as one of a pair to form a floating mark as in certain types of stereoscopes. [14]
5138	Sag Correction (Tape)	See tape: sag correction. [14]
5139	Sailing: Great Circle	Any sailing when a great circle track is involved. [14]
5140	Satellite: Artificial	An object placed by man in orbit around the earth, or other celestial body. See navigational (or navigation) satellite. [14]
5141	Sextant: Hydrographic	See sextant: sounding. [14]
5142	Shallow Water Tide(S)	See tide. [14]
5143	Signal: Tidal Current	A signal or message conveying information on condition of tidal current in the area in question. [14]
5144	Signal: Triangulation	A rigid structure erected close or over a triangulation station. Also any object, natural or artificial, whose position is obtained in a triangulation survey. The term may be applied to a structure whose position is determined by triangulation, but whose primary purpose is to serve later in a hydro-graphic or topographic survey, when it may become known as a hydrographic or topographic signal. [14]
5145	Sounding(S): Detached	Those soundings, including least depths on shoals, whose positions were accurately located. See position: detached. [14]
5146	Sounding: Fixed Angle	A method consisting in sounding along the arcs of circles subtended by two objects whose position is known. For each arc, an angle remains constant (fixed angle) and the second angle, between another pair of objects, defines the position of the vessel along the arc. By varying the fixed angle successively by equal amounts, a series of lines of sounding covering the area systematically can be run. See fixed angle plot. [14]
5147	Station: Astronomical	A point on the earth whose position has been determined by observations of celestial bodies. [14]
5148	Station: Intersection	In surveying, an object whose horizontal position is determined by observations from other stations, no observations being made at the object itself. Where the object is observed from only two stations, the position is termed a no check position as there is no proof that such observations are free from blunders. Intersection stations are either objects which would be difficult to occupy with an instrument, or survey signals whose positions can be determined with sufficient accuracy without being occupied. Also called intersected point. [14]
5149	Steady-State Forecast	A weather prediction based on the past movement of surface weather systems. It assumes that the systems will move in the same direction and at approximately the same speed as they have been moving. Also called trend forecasting. [1]
5150	Supplementary Station	See station. [14]
5151	Survey: Oceanographic	A study or examination of any physical, chemical, biological, geological or geophysical condition in the ocean, or any part of it. An expedition to gather data, samples or information to conduct such studies or examination. [14]
5152	Taiga (Boreal Forest)	The open northern part of the coniferous forest. Taiga also refers to subpolar climate. [1]
5153	Telemeter: Electronic	An electronic device that measures the phase difference or transit time between a transmitted electromagnetic impulse of known frequency and speed and its return. [14]
5154	Telescope: Reflecting	A telescope which collects light by means of a concave mirror. [14]
5155	Telescope: Refracting	A telescope which collects light by means of a lens or system of lenses. [14]
5156	Temperature Inversion	N oceanography, a layer in which temperature increases with depth. Also called inversion layer. [14]
5157	Template (Or Templet)	A pattern or guide, usually constructed of paper, plastic, or metal, used to shape, delimit, or locate an area. A device used in radial triangulation to represent the aerial photograph; the template provides a record of the directions of radials taken from the photograph. [14]
5158	Terrestrial Longitude	See longitude. [14]
5159	Terrestrial Magnetism	See geomagnetism. [14]
5160	Terrigenous Sediments	Deposits consisting of debris derived from the erosion of land areas and usually deposited in the shallow parts of the sea. [14]
5161	Theodolite: Direction	A theodolite in which the graduated horizontal circle remains fixed during a series of observations, the telescope being pointed on a number of signals or objects in succession, and the direction of each read on the circle, usually by the use of micrometer microscopes. [14]
5162	Thermometer: Deep Sea	A thermometer for ascertaining the temperature of sea water at any depth. See thermometer: protected reversing, thermometer: reversing, thermometer: unprotected reversing. [14]
5163	Thermometer: Dry-Bulb	That of the two thermometers of a psychrometer whose bulb is bare and which indicates the air temperature. [14]
5164	Thermometer: Wet-Bulb	That of the two thermometers of a psychrometer whose bulb is wet and covered by a film of pure water or ice. [14]
5165	Tidal (Or Tide) Cycle	A complete set of tidal conditions, as those occurring during a tidal day, lunar month or metonic cycle. [14]
5166	Time: Daylight Saving	A variation of zone time, usually one hour ahead of that time. Sometimes called summer time. [14]
5167	Time: Greenwich Civil	See time: Greenwich mean. [14]
5168	Track: Dead Reckoning	A line representing successive dead reckoning positions of a craft. [14]
5169	Transient Thermocline	See thermocline. [14]
5170	Traverse: Plane Table	A graphical traverse executed by plane table methods. [14]
5171	Triangulation: Radial	See radial triangulation. [14]
5172	Underwater Navigation	See navigation. [14]
5173	Unifilar Magnetometer	See magnetometer. [14]
5174	Unrecoverable Station	See station. [14]
5175	Variation Of The Pole	A wandering of the poles of the figure of the earth with respect to its poles of rotation. [14]
5176	Visibility: Radius Of	The radius of a circle limiting the area in which an object can be seen under specified conditions. [14]
5177	World Geodetic System	A global geodesic reference system developed by the USA for satellite position fixing and recommended by IHO for hydrographic and cartographic use. [14]
5178	Active Tracking System	A satellite system which operates by transmission of signals to and receipt of responses from the satellite. [14]
5179	Alt-Azimuth Instrument	An instrument equipped with both horizontal and vertical graduated circles, for the observation of horizontal and vertical directions or angles. [14]
5180	Altimeter: Pulse Radio	See altimeter: radio. [14]
5181	Astronomic(Al) Azimuth	See azimuth. [14]
5182	Astronomic(Al) Control	See control. [14]
5183	Astronomic(Al) Equator	See equator. [14]
5184	Astronomic(Al) Station	See station. [14]
5185	Astronomic(Al) Transit	See transit. [14]
5186	Atmospheric Refraction	See refraction. [14]
5187	Atmospheric Stagnation	A condition of light winds and poor vertical mixing that can lead to a high concentration of pollutants. Air stagnations are most often associated with fair weather, an inversion, and the sinking air of a high-pressure area. [1]
5188	Axis Of Optical System	The line formed by the coinciding principal axes of the series of optical elements. [14]
5189	Baseline: Archipelagic	Archipelagic baselines are straight lines joining the outermost points of the outermost islands and drying reefs of an archipelago. [14]
5190	Beacon: Identification	An aeronautical and/or radio and/or light beacon emitting a coded signal by means of which a particular reference point can be identified. [14]
5191	Bimetallic Thermometer	A temperature-measuring device usually consisting of two dissimilar metals that expand and contract differentially as the temperature changes. [1]
5192	Bottom Characteristics	Designations used on survey and nautical charts to indicate the consistency, colour, and classification of the sea bottom. Also called nature of the bottom, character of the bottom. [14]
5193	Calibration Of Compass	See swinging ship. [14]
5194	Chain Of Triangulation	See triangulation: arc of. [14]
5195	Chart: Gravity Anomaly	A chart on which current gravity anomalies are graphically depicted. [14]
5196	Chronometer Correction	The amount to be added algebraically to the time of the chronometer to obtain the correct time. [14]
5197	Collimation Adjustment	The process of bringing the line of collimation of a telescope into close agreement with the collimation axis. [14]
5198	Continental Borderland	A region adjacent to a continent, normally occupied by or bordering a continental shelf, highly irregular, with depths well in excess of those typical of a continental shelf. [14]
5199	Coordinates: Celestial	Any set of coordinates used to define a point on the celestial sphere. The horizon, celestial equator and ecliptic systems of celestial coordinates are based on the celestial horizon, celestial equator and ecliptic respectively, as the primary great circle. [14]
5200	Coordinates: Origin Of	The point of intersection of the coordinate axes, from which the coordinates are reckoned. In mathematical treaties, this origin is usually given the coordinates 0,0; in surveying, however, it is standard practice to give this origin, coordinates having large positive numerical values, thereby avoiding the use of negative coordinates. Also called point of origin. See coordinates: false. [14]
5201	Coordinates: Spherical	A system of polar coordinates in which the origin is the center of a sphere and the points all lie on the surface of a sphere. The polar axis of such a system cuts the sphere at its two poles. [14]
5202	Cross Wires (Or Hairs)	Wires or etched lines, at right angles, held at the focal plane of an astronomical or sighting telescope. See also reticle. [14]
5203	Cylindrical Projection	See projection. [14]
5204	Difference Of Latitude	The angular distance between the parallels of two places measured on a meridian. [14]
5205	Differential Levelling	See levelling. [14]
5206	Differential Shrinkage	In mapping, the difference in unit contraction along the grain structure of the material as compared to the unit contraction across the grain structure; frequently refers to photographic film and papers and to map materials in general. [14]
5207	Double Zenith Distance	See zenith distance. [14]
5208	Dust Devil (Whirlwind)	A small but rapidly rotating wind made visible by the dust, sand, and debris it picks up from the surface. It develops best on clear, dry, hot afternoons. [1]
5209	Electric Submerged Log	See log. [14]
5210	Ellipsoid Of Reference	See reference spheroid. [14]
5211	Extinction Coefficient	A measure of the space rate of diminution or extinction, of any transmitted light. In oceanography, the measure of attenuation of downward directed light radiation in the sea. [14]
5212	Floating Triangulation	See triangulation. [14]
5213	Frequency Of Soundings	See density of soundings. [14]
5214	Frequency: Medium (Mf)	See frequency: radio. [14]
5215	Geocentric Coordinates	See coordinates. [14]
5216	Graphic Control Survey	See survey. [14]
5217	Gyroscope: Directional	A gyroscopic device used to indicate a selected horizontal direction for a limited time. It requires periodic resetting dependent upon the gyro precession rate or change in the desired heading or horizontal direction. [14]
5218	Installation: Offshore	Man-made structure usually built for the exploration or exploitation of marine resources, marine scientific research, tide observations, etc. [14]
5219	International Shipping	Shipping engaged on international voyages. [14]
5220	Interrogator-Responsor	See interrogator and responsor. [14]
5221	Isogonal (Or Isogonic)	(Adj.). Having equal angles. [14]
5222	Isogonal (Or Isogonic)	(n.). See isogonic line. [14]
5223	Lagging Of The Tide(S)	The periodic retardation in the time of occurrence of high and low water due to changes in the relative positions of the moon and the sun. [14]
5224	Lagging Of The Tide(S)	The retardation in the time of occurrence of high and low water due to changes in the relative positions of the moon and the sun. The opposite effect is called priming of the tide(s). See also daily retardation. [14]
5225	Latitude: Astronomical	Angular distance between the direction of gravity and the plane of the equator. Astronomical latitude is the latitude which results directly from observations on celestial bodies, uncorrected for deflection of the vertical. [14]
5226	Layer Depth Prediction	Predetermining the depth to the top of the thermocline over a given ocean area. [14]
5227	Light: Group-Occulting	An occulting light in which a group of two or more eclipses, which are specified in number, is regularly repeated. [14]
5228	Line Of Constant Scale	Any line on a photograph which is parallel to the true horizon or to the isometric parallel. [14]
5229	Longitude: Terrestrial	The intercepted arc of equator, or the angle at the pole, between the meridian of a point on the earth, and the prime meridian, measured eastward or westward from the prime meridian through 180° and labelled e or w to indicate the direction of measurement. [14]
5230	Low Oblique Photograph	See photograph. [14]
5231	Magnetic Annual Change	The amount of secular change in the earth's magnetic field which occurs in one year. Also referred to as annual change. [14]
5232	Magnetism: Terrestrial	See geomagnetism. [14]
5233	Magnetometer: Unifilar	A magnetometer, designed for use on shore, employed to measure the horizontal intensity of the earth's magnetism; it can also be used to determine variation. [14]
5234	Mean Daily Temperature	The average of the highest and lowest temperature for a 24-hour period. [1]
5235	Mean Sounding Velocity	Mean values for velocity of sound through the vertical water column of specific depths based on different velocities of sound in different sections of the column. These values yield more nearly correct depths when sonic depth finders are used. The velocity of sound at any specific depth may differ considerably from the mean. [14]
5236	Meridian: Astronomical	A line on the surface of the earth connecting points having the same astronomical longitude. Because the deflection of the vertical is not the same at all points, an astronomical meridian is an irregular line, not lying in a single plane. Also called terrestrial meridian. [14]
5237	Micrometer: Impersonal	See micrometer: transit. [14]
5238	Military Practice Area	See exercise area. [14]
5239	Navigation: Electronic	Navigation by means of electronic equipment. The expression 'electronic navigation' is more inclusive than radio navigation, since it includes navigation involving any electronic device or instrument. [14]
5240	Navigation: Hyperbolic	Navigation by the use of hyperbolic lines of position. [14]
5241	Navigation: Long Range	Navigation requiring only aids usable at long range, relatively few of which could provide world coverage. The opposite is short range navigation. [14]
5242	Navigation: Underwater	The navigation of a submerged vessel. Occasionally called submarine navigation. [14]
5243	Navigational Astronomy	See astronomy: nautical. [14]
5244	Navigational Planet(S)	See planet(s): navigational. [14]
5245	New Edition (Of Chart)	In British terminology, a new printing of an existing chart embodying the latest information received in the hydrographic department. The chart is entirely revised throughout and modernized in style, all copies of the chart in circulation being cancelled. When a new edition is published the large and small corrections dates are removed (these corrections being embodied in the new edition). In US Terminology, a new printing of an existing chart embodying corrections that have become so extensive or of such importance to navigation as to render all previous printings obsolete. [14]
5246	Nitrogen Dioxide (No2)	A reddish-brown gas, produced by natural bacterial action in soil and by combustion processes at high temperatures. In the presence of sunlight, it breaks down into nitric oxide and atomic oxygen. In polluted air, nitrogen dioxide acts as an agent in the production of photochemical smog. [1]
5247	Oceanographic Features	Physical qualities characterizing the state of environment in water bodies of the world's oceans. These features include temperature and salinity, electric conductivity, density, hydrostatic pressure, transparency, the range and character of tidal and other water level oscillations, the speed and direction of currents, the characteristics of waves and ice, etc. [14]
5248	Omnidirectional Beacon	See omnirange. [14]
5249	Orthometric Correction	The correction to elevations which takes into account the spheroidal shape of the earth and brings the elevations to their true height above mean sea level. [14]
5250	Parallax: Heliocentric	See parallax: annual. [14]
5251	Parallel: Astronomical	A line on the surface of the earth which has the same astronomical latitude at every point. Because the deflection of the vertical is not the same at all points on the earth, an astronomical parallel is an irregular line, not lying in a single plane. [14]
5252	Permeability: Magnetic	See magnetic permeability. [14]
5253	Photogrammetric Camera	See camera. [14]
5254	Photogrammetric Survey	See survey. [14]
5255	Photogrammetry: Aerial	Photogrammetry utilizing aerial photographs. [14]
5256	Photograph Coordinates	See coordinates. [14]
5257	Photograph: Horizontal	Photograph taken with the camera axis horizontal. [14]
5258	Position: Astronomical	A point on the earth whose coordinates have been determined as a result of observation of celestial bodies. The expression is usually used in connection with positions on land determined with great accuracy for survey purposes. A point on the earth, defined in terms of astronomical latitude and longitude. [14]
5259	Preferred Channel Mark	A distinctive lateral mark used to indicate both the point at which a channel divides and the channel that has been designated as preferred channel. [14]
5260	Primary Air Pollutants	Air pollutants that enter the atmosphere directly. [1]
5261	Priming Of The Tide(S)	The acceleration in the times of occurrence of high and low water due to changes in the relative positions of the moon and the sun. The opposite effect is called lagging of the tides. [14]
5262	Program (Or Programme)	The complete sequence of computer instructions and routines necessary to solve a data processing problem. [14]
5263	Projection: Equivalent	See projection: equal area. [14]
5264	Radio Acoustic Ranging	Determining distance by a combination of radio and sound, the radio being used to determine the instant of transmission or reception of the sound, and distance being determined by the time of transit of sound, usually in water. Also called radio acoustic sound ranging. See distance finding station, echo ranging, sonobuoy. [14]
5265	Radio Signals: List Of	See list of radio signals. [14]
5266	Range Height Indicator	A scope which simultaneously indicates range and height of a radar target. [14]
5267	Reduction To Sea Level	A reduction applied to a measured horizontal length on the earth's surface to reduce it to the surface of the sea level datum. [14]
5268	Reversing Water Bottle	See water bottle. [14]
5269	Root Mean Square Error	See error: standard. [14]
5270	Sea Bottom Temperature	The temperature measured at or close to sea floor. [14]
5271	Secondary Tide Station	See station: tide. [14]
5272	Semicircular Deviation	See deviation. [14]
5273	Short Range Navigation	See navigation. [14]
5274	Side Scan Sonar Mosaic	An assembly of side scan sonar images whose edges have been cut or torn and matched to form a continuous side scan sonar image. [14]
5275	Simultaneous Altitudes	Altitudes of two or more celestial bodies observed at the same time. [14]
5276	Sounding(S): No Bottom	(US Terminology). Soundings where the bottom was not reached because the general depths were too great for the method of measurement. [14]
5277	Split Line Of Sounding	A line of sounding run to fill a void when the maximum spacing of principal lines is exceeded. [14]
5278	Station: Oceanographic	The geographic location at which any set of oceanographic observations are gathered. The station may be occupied by a mobile platform (a ship) or a fixed platform such as a tower. [14]
5279	Station: Supplementary	An auxiliary station, established to increase the number of control stations in a given area, or to place a station in a desired location where it is impracticable or unnecessary to establish a principal station. Also called secondary station. [14]
5280	Station: Trigonometric	See station: triangulation. [14]
5281	Station: Unrecoverable	A triangulation station that cannot be found and cannot be included in the triangulation to connect it with a new datum. Sometimes called 'lost' station. [14]
5282	Stationary Wave Theory	A theory which assumes that the basic tide motion in the open ocean consists of a system of standing wave oscillations; progressive waves are of secondary importance except where the tide advances into tributary waters. [14]
5283	Submarine Sound Signal	See sound signal. [14]
5284	Submarine Transit Lane	a lane where submarines may navigate under water or at the surface. [14]
5285	Subpermanent Magnetism	See magnetism: permanent. [14]
5286	Subtropical Jet Stream	The jet stream typically found between 20° and 30° latitude at altitudes between 12 and 14 km. [1]
5287	Surface Boundary Layer	See ground layer. [14]
5288	Survey: Reconnaissance	A hasty preliminary survey of a region made to provide some advance information regarding the area which may be useful, pending the execution of more complete surveys. Also called preliminary survey. [14]
5289	Temperature Lapse Rate	Rate of decrease of temperature with increasing height; usually an average rate over a distance, for example 100 meters, is considered. [14]
5290	Terrestrial Navigation	The kind of navigation which uses marks ashore for positioning. [14]
5291	Theodolite: Face(S) Of	See face(s) of theodolite. [14]
5292	Thermocline: Transient	A small decrease in vertical temperature observed above the thermocline. It is a short-term phenomenon associated primarily with diurnal heating and wind mixing. [14]
5293	Thermometer: Reversing	A deep-sea thermometer that records temperature at the desired depth upon being inverted and thereafter retains its reading until returned to the first position. Reversing thermometers are generally used in pairs on water bottles. [14]
5294	Thermometric Levelling	See levelling. [14]
5295	Three-Point Fix Method	One of the principal methods used on inshore hydrographic surveys for establishing the position of the survey vessel. It involves the measurement with sextants of two angles between three known stations, the middle station being common to both angles, and plotting the vessel's position gra-phically with a three-arm protractor. [14]
5296	Tide: Leeward (Or Lee)	A tidal current setting in the same direction as that in which the wind is blowing. Also called leeward tidal current. [14]
5297	Traverse: Astronomical	A traverse in which the geographic(al) positions of the stations are obtained from astronomical observations, and lengths and azimuths of lines are obtained by computation. [14]
5298	Tropic Lower Low Water	The lower low water of tropic tides. [14]
5299	Unidirectional Antenna	See antenna. [14]
5300	Universal Time 0 (Ut0)	The uncorrected time of the earth's rotation as measured by the transit of stars across the observer's meridian. This rotation is referred to a fiducial mark on the ecliptic which approximates the position of the mean sun. [14]
5301	Universal Time 1 (Ut1)	Ut0 corrected for polar motion. [14]
5302	Universal Time 2 (Ut2)	Ut1 corrected for seasonal variations in the earth's rotation. [14]
5303	Want Of Correspondence	See parallax: y-. [14]
5304	Wave: Love (Or Q-Wave)	A transverse wave propagated along the boundary of two elastic media which both have rigidity, i.e. Both media must be capable of propagating transverse waves. A surface seismic wave in which the particles of an elastic medium vibrate transverse to the direction of the wave's travel, with no vertical component. [14]
5305	Weather Chart (Or Map)	See chart. [14]
5306	Absorption: Atmospheric	Transformation of radiant energy into thermal, mechanical, electrical, etc. Energy, by interaction with atmospheric constituents. [14]
5307	Acceleration Of Gravity	The acceleration of a freely falling body caused by the force of gravity. [14]
5308	Age Of Phase Inequality	The time interval between new or full moon and the maximum effect of these phases upon the range of tide or the speed of the tidal current. [14]
5309	Air Quality Index (Aqi)	An index of air quality that provides daily air pollution concentrations. Intervals on the scale relate to potential health effects. [1]
5310	Antenna: Unidirectional	An antenna having a single well-defined direction of maximum radiation intensity or maximum gain. [14]
5311	Arc To Chord Correction	The quantity used by seamen to correct a great circle bearing of a point b from a point a to a Mercator bearing, and usually referred to as the half convergency on the Mercator projection, this quantity is equal to half the convergency, on the spheroid, of the meridians through the two points being considered. Also called conversion angle. See convergence of the meridians. [14]
5312	Arctic Oscillation (Ao)	A reversal of atmospheric pressure over the arctic that produces changes in the upper-level westerly winds over northern latitudes. These changes in upper-level winds influence winter weather patterns over North America, Greenland, and Europe. [1]
5313	Artificial Installation	See installation offshore. [14]
5314	Astronomic(Al) Latitude	See latitude. [14]
5315	Astronomic(Al) Meridian	See meridian. [14]
5316	Astronomic(Al) Parallel	See parallel. [14]
5317	Astronomic(Al) Position	See position. [14]
5318	Astronomic(Al) Traverse	See traverse. [14]
5319	Astronomic(Al) Triangle	The triangle on the celestial sphere formed by arcs of great circles connecting the celestial pole, the zenith and the celestial body. Also called navigational triangle. [14]
5320	Astronomic(Al) Twilight	See twilight. [14]
5321	Azimuth: Astronomic(Al)	The angle between the astronomic meridian plane of the observer and the plane containing the observed point and the vertical of the observer. [14]
5322	Beacon: Omnidirectional	See omnirange. [14]
5323	Bench Mark (Benchmarks)	A permanent, stable object containing a marked point of known elevation with respect to a datum used as a reference level for tidal observations or as a control point for levelling. [14]
5324	Calibrated Focal Length	See focal length. [14]
5325	Camera: Photogrammetric	A general term applicable to cameras used in any of the several branches of photogrammetry. [14]
5326	Centering (Or Centring)	The placing of an instrument with its vertical axis in the vertical through the ground mark. The setting of lenses of an optical instrument in such a manner that their optical axes are in the same straight line. [14]
5327	Chart Evaluation Survey	The chart evaluations surveys (CES) program is designed to: 1. Resolve all deficiencies reported or discovered. (a deficiency is defined as charted information that can be made more complete through field examination, or information which should be charted but is not.) 2. Evaluate the adequacy/accuracy of hydrographic information on existing charts. 3. Verify or revise information published in the appropriate coast pilot. 4. Conduct user evaluation and public relations efforts to provide an awareness of products and obtain user input. [14]
5328	Check Lines Of Sounding	Sounding lines run after completing the main system of sounding lines for the purpose of checking them. See also cross lines of sounding. [14]
5329	Climatological Forecast	A weather forecast, usually a month or more in the future, which is based upon the climate of a region rather than upon current weather conditions. [1]
5330	Compass Adjustment Buoy	A buoy placed at a favorable location to assist a vessel to adjust its compass or swing ship. Also called swinging buoy. See also swinging ship. [14]
5331	Continental Shelf Limit	The limit of the continental shelf or continental margin determined in accordance with the provisions of the united nations convention on the law of the sea. [14]
5332	Continuous Strip Camera	See camera. [14]
5333	Controls Of Temperature	The main factors that cause variations in temperature from one place to another. [1]
5334	Coordinates: Geocentric	Coordinates that define the position of a point with respect to the center of the earth. See latitude: geocentric. The term 'geocentric longitude' is never used, as the quantity which it would designate is the same as geodetic longitude. [14]
5335	Coordinates: Photograph	A system of coordinates, either rectangular or polar, to define the position of a point on a photograph. [14]
5336	Corrected Establishment	See lunitidal interval. [14]
5337	Correction Of Soundings	The correction of the observed depths for any departure from true depth due to the method of sounding or to a fault in the measuring apparatus. See also reduction of soundings. [14]
5338	Correction: Atmospheric	The statistical removal of meteorological effects from mean sea level changes. [14]
5339	Correction: Ionospheric	A correction for errors introduced by ionospheric refraction occurring when signals travel through the ionosphere. [14]
5340	Cross Lines Of Sounding	Sounding lines run approximately at right angles to those of normal direction, frequently useful when examining shoals. Cross lines are also run after completing the main system of sounding lines, with the purpose of checking them. [14]
5341	Cruise Line Of Sounding	See track line of sounding. [14]
5342	Datum: Vertical Control	Any level surface (e.g., mean sea level) taken as a surface of reference from which to reckon elevations. Also called datum level, reference level, reference plane, levelling datum, datum for heights. See also datum plane. [14]
5343	Dead Reckoning Position	See position. [14]
5344	Deviation: Semicircular	Deviation which changes sign (e or w) approximately each 180° change of heading. [14]
5345	Dip (Or Dipping) Needle	A magnetic needle suspended in such a manner as to be free to rotate about a horizontal axis. See dip circle. [14]
5346	Discrepancy In Position	The difference between a reckoned and an observed position at the same time. [14]
5347	Eccentricity Of Ellipse	The ratio of the distance between the center and a focus of an ellipse to the length of its semi-major axis. [14]
5348	Error: Root Mean Square	See error: standard. [14]
5349	Estimated Position (Ep)	See position. [14]
5350	Facility (Navigational)	See aid to navigation. [14]
5351	Geographic(Al) Latitude	See latitude. [14]
5352	Geographic(Al) Meridian	See meridian. [14]
5353	Geographic(Al) Parallel	See parallel. [14]
5354	Geographic(Al) Position	See position. [14]
5355	Grade Correction (Tape)	See tape: grade correction. [14]
5356	High Oblique Photograph	See photograph. [14]
5357	Highland (Or Highlands)	High or elevated land; a lofty headland or cliff. The mountainous or elevated part of any country; occasionally also in the names of geographical districts. [14]
5358	Hydrostatic Equilibrium	The state of the atmosphere when there is a balance between the vertical pressure gradient force and the downward pull of gravity. [1]
5359	Hydrostatic Instability	See instability: static. [14]
5360	Indian Spring Low Water	An arbitrary tidal datum approximating the level of the mean of the lower low water at spring tides. It was first used in waters surrounding India. Also called Indian tide plane. [14]
5361	International Date Line	See date line. [14]
5362	Interpupillary Distance	The distance between centers of the eye pupils of an individual. Also called eye base and used interchangeable with interocular distance. [14]
5363	Ionospheric Disturbance	A sudden outburst of ultraviolet light on the sun, known as a solar flare, which produces abnormally high ionization in the region of the d-layer. The result is a sudden increase in radio wave absorption, with particular severity in the upper medium and lower high frequencies. It has negligible effects on the heights of the reflecting/refracting layers and, consequently, upon critical frequencies, but enormous transmission may occur. [14]
5364	Landslide (Or Landslip)	The sliding down of a mass of land on a mountain or cliff-side; land which has so fallen. [14]
5365	Levelling (Or Leveling)	The operation of determining differences of elevation between points on the surface of the earth; the determination of the elevation of points relative to some arbitrary or natural level surface called a datum. Also called differential levelling. [14]
5366	Levelling: Thermometric	The determination of elevations above sea level from observed values of the boiling point of water. See hypsometer. [14]
5367	Light (Or Lighted) Buoy	See buoy. [14]
5368	Light: Group Very Quick	A light in which very quick flashes are combined in groups including the same number of flashes (repetition rate : 80-159 per minute) and in which groups are repeated at regular intervals. [14]
5369	Log: Electric Submerged	An electrically-operated log installed inside the hull of the vessel with a tube extending through the hull into the water. [14]
5370	Longitude: Astronomical	The angle between the plane of the celestial meridian and the plane of an initial meridian, arbitrarily chosen. Astronomical longitude is the longitude which results directly from observations on celestial bodies, uncorrected for deflection of the vertical. [14]
5371	Magnetic Field Strength	See magnetic field intensity. [14]
5372	Magnetic Lines Of Force	Closed lines indicating by their direction the direction of magnetic influence. [14]
5373	Magnetic Observation(S)	See observation. [14]
5374	Magnetic Secular Change	The temporal variation in the value of a magnetic element which occurs over a period of years. [14]
5375	Magnetism: Subpermanent	See magnetism: permanent. [14]
5376	Magnetometer: Flux-Gate	An instrument which uses a wire wound saturable core inductor to measure the earth's magnetic field. [14]
5377	Maritime Polar Air Mass	An air mass characterized by low temperatures and high humidity. [1]
5378	Mean Annual Temperature	The average temperature at any given location for the entire year. [1]
5379	Mean Low Water (M.L.W.)	The average height of all low waters at a place over a 19-year period. [14]
5380	Middle-Latitude Cyclone	A cyclonic storm that most often forms along a front in middle and high latitudes. Also called a middle- latitude cyclonic storm, a depression, and a low. It is not a tropical storm or hurricane. See extratropical cyclone. [1]
5381	Middle-Latitude Cyclone	A cyclonic storm that most often forms along a front in middle and high latitudes. Also called a middle- latitude cyclonic storm, a depression, and a low. It is not a tropical storm or hurricane. See extratropical cyclone. [1]
5382	Multi-Beam Echo Sounder	a type of swath(e) sounding system in which the equipment emits a timed pulse of sound that is narrow in the fore-aft direction and wide in the across track direction. The reflected sound is received by several receivers arranged as an array. By use of signal processing of the signal received at combinations of the receivers a much larger number, potentially many hundreds, of acoustic receive beam angles are formed. For each receive beam the time interval between emission and reception of the reflected sound is converted into a range. Geometry is then used to convert each range and receive beam angle to depths and also to position these depths within the swath(e) on the sea floor. Mbes systems may also be referred to as beam-formers. [14]
5383	Multicell Thunderstorms	Thunderstorms often in a line, each of which may be in a different stage of its life cycle. [1]
5384	Navigation: Short Range	Navigation employing only aids usable at short ranges. The opposite is long range navigation. [14]
5385	Navigational Parameters	All data characterizing the position and motion of a vessel in a system of coordinates. [14]
5386	Night Effect (Or Error)	See error: polarization. [14]
5387	Nomogram (Or Nomograph)	A diagram showing, to scale, the relationship between several variables in such manner that the value of one which corresponds to known values of the others can be determined graphically. See conversion scale, conversion table. [14]
5388	North Geographical Pole	See pole: geographical. [14]
5389	Odometer (Or Hodometer)	An instrument for measuring the distance travelled by a craft. See also speedometer. [14]
5390	Omnidirectional Antenna	See antenna. [14]
5391	Orthographic Projection	See projection. [14]
5392	Parallel Of Declination	A circle of the celestial sphere parallel to the celestial equator. Also called celestial parallel. [14]
5393	Photogrammetric Control	See control. [14]
5394	Photograph: Low Oblique	An oblique photograph in which the apparent horizon is not included within the field of view. [14]
5395	Photograph: Terrestrial	A photograph taken by a camera located on the ground. Sometimes called ground photograph. [14]
5396	Planet(S): Navigational	The four planets commonly used for celestial observations: Venus, Mars, Jupiter, and Saturn. [14]
5397	Precipitation Intensity	Amount of precipitation collected in unit time interval. See rainfall amount. [14]
5398	Prognostic Chart (Prog)	A chart showing expected or forecasted conditions, such as pressure patterns, frontal positions, contour height patterns, and so on. [1]
5399	Projection: Cylindrical	A projection produced by projecting the geographical meridians and parallels onto a cylinder which is tangent to (or intersects) the surface of a sphere, and then developing the cylinder into a plane. [14]
5400	Projection: Perspective	The representation of a figure on a surface, either plane or curved, by means of projecting lines emanating from a single point, which may be infinity. Also called geometric projection. [14]
5401	Properties Of Sea Water	See sea water, salinity. [14]
5402	Quarter-Diurnal Tide(S)	See tide. [14]
5403	Radiative Forcing Agent	Any factor (such as increasing greenhouse gases and variations in solar output) that can change the balance between incoming energy from the sun and outgoing energy from the earth and the atmosphere. [1]
5404	Rectangular Coordinates	See coordinates. [14]
5405	Refraction: Atmospheric	Refraction resulting when a ray of radiant energy passes obliquely through the atmosphere. It may be called astronomical refraction if the ray enters the atmosphere from outer space, or terrestrial refraction if it emanates from a point on or near the surface of the earth. [14]
5406	Regression Of The Nodes	Precessional motion of a set of nodes. The expression is used principally with respect to the moon, the nodes of which make a complete westerly revolution in approximately 18.6 years. [14]
5407	Representative Fraction	See scale: natural. [14]
5408	Run A Line Of Soundings	(v.t.). To obtain soundings along a line of sounding, for surveying purposes. [14]
5409	Sargasso (Or Sargassum)	A certain type of seaweed, or more generally, a large floating mass of this seaweed. [14]
5410	Semidiameter Correction	A correction due to semidiameter, particularly that sextant altitude correction resulting from observation of the upper or lower limb of a celestial body, rather than the center of that body. [14]
5411	Short-Term Distribution	Probability distribution of a variable within a short interval of time during which conditions are assumed to be statistically constant. NOTE The interval chosen is most often the duration of a sea state. [15]
5412	Slide (Or Sliding) Rule	A device used for performing rapid computations involving multiplication, division, proportion, roots, and powers. It has a body like a ruler, but with a sliding section. Both body and sliding section are graduated with numbers according to logarithmic scales. [14]
5413	Slope And Height Factor	In the measurement of distances with tellurometer, a factor to be reckoned when reducing distances to the spheroid. It takes into account the mean height of the stations (master and remote units) and the slope of the line. [14]
5414	Slope Correction (Tape)	See tape: grade correction. [14]
5415	Sound Signal: Submarine	A sound signal transmitted through water. [14]
5416	South Geographical Pole	See pole: geographical. [14]
5417	Survey: Graphic Control	A skeleton survey made by plane table for the purpose of (a) locating the hydrographic signals, (b) locating additional control from aerial surveys and clarification of indefinite detail on photographs, (c) a combination of the two. [14]
5418	Survey: Photogrammetric	A survey utilizing either terrestrial or aerial photographs. [14]
5419	Synoptic Chart (Or Map)	See chart (or map): weather. [14]
5420	Tide-Predicting Machine	An instrument that computes, sometimes for years in advance, the times and heights of high and low waters at a reference station by mechanically summing the harmonic constituents of which the tide is composed. [14]
5421	Tide-Producing Force(S)	That part of the gravitational attraction of a celestial body which is effective in producing the tides on earth. The sun and moon are the principal astronomic bodies that have a tide-producing effect. The force varies approximately as the mass of the attracting body and inversely as the cube of its distance. Also called tide-generating force. [14]
5422	Traffic Separation Line	see separation zone [14]
5423	Traffic Separation Zone	See separation zone [14]
5424	Transitional Water Wave	See wave. [14]
5425	Triangulation: Floating	In hydrographic surveying, a triangulation that may be carried out by means of anchored buoys when surveying at such a distance from the land that the signals on the shore cannot be directly used for locating the soundings. Floating triangulation can be either connected to and extended from the stations of a shore triangulation or of a fully floating type in which case the positions of the buoys are obtained by means of observations and measurements taken at sea. Buoys are anchored in such a position as to provide a framework for surveying the area. [14]
5426	Triangulation: Order Of	See triangulation classification. [14]
5427	Trigonometric Levelling	See levelling. [14]
5428	Tropic Higher Low Water	The higher low water of tropic tides. [14]
5429	Tropic Lower High Water	The lower high water of tropic tides. [14]
5430	Tropospheric Scattering	Diffusion of electromagnetic waves when traversing the troposphere. See also: scattering. [14]
5431	Ultrasonic Depth Finder	See echo sounder. [14]
5432	Underway (Or Under Way)	(adv.). Without moorings; not secured in any way to the ground or a wharf. In motion, particularly the start of such motion after a standstill. [14]
5433	Undulation Of The Geoid	The distance between the mathematical reference spheroid and the geoid. [14]
5434	Visual Line Of Position	A line of position determined by visual observation of a landmark, aid to navigation, etc. [14]
5435	Water Bottle: Reversing	A water bottle specially designed for use in deep sea waters. The bottle is lowered by wire and can be closed watertight at any desired depth, by means of a messenger allowed to slide down the wire and strike the reversing mechanism making the bottle turn upside down. Thus the enclosed water sample is not contaminated by water at higher levels or lost by leakage after the bottle is brought on board. Reversing thermometers are attached to reversing water bottles. See ekman bottle and nansen bottle. [14]
5436	Wollaston Current Meter	A current meter similar but much larger and heavier than the ekman current meter. It is equipped with recording mechanisms and is suitable for measuring currents up to six knots. The wollaston current meter is designed for use from ships at anchor. [14]
5437	Zenith Distance: Double	A value of twice the zenith distance of an object, obtained by observation and not by mathematical process. [14]
5438	Antenna: Omnidirectional	An antenna having essentially uniform response in azimuth and a directional pattern in elevation. [14]
5439	Archipelagic Baseline(S)	See baseline. [14]
5440	Astronomic(Al) Longitude	See longitude. [14]
5441	Automatic Volume Control	See automatic gain control. [14]
5442	Between-The-Lens Shutter	See shutter. [14]
5443	Broken Telescope Transit	See transit. [14]
5444	Buoy: Light (Or Lighted)	A buoy with a light having definite characteristics for detection and identification during darkness. See characteristics of light. [14]
5445	Calibration: Direct Base	The calibration of a positioning system with the help of one or more baselines of known length, which is determined with an instrument having an accuracy superior to that of the positioning system. [14]
5446	Camera: Continuous-Strip	A camera in which a continuous-strip exposure is made by rolling the film continuously past a narrow slit opening at a speed proportional to the ground speed of the aircraft. [14]
5447	Characteristics Of Light	All particularities of a light, such as colour, period, group number, visibility, height above sea level and character. Also called light characteristics. See also group. [14]
5448	Chart (Or Map): Synoptic	See chart (or map): weather. [14]
5449	Chart: Radionavigational	A chart with additional details for the determination of a vessel's position with the aid of radionavigation systems. [14]
5450	Circle Of Equal Altitude	A small circle on the surface of the earth at every point of which, at the instant of observation, the observed celestial body (sun, star, or planet) has the same altitude and, therefore, the same zenith distance. [14]
5451	Circum-Meridian Altitude	See altitude: ex-meridian. [14]
5452	Clearance: Safe Overhead	The height above the vertical control datum at which the highest points of a ship can pass under an overhead power cable without risk of electrical discharge from the cable to the ship or without making contact with a bridge. [14]
5453	Configuration Of Terrain	The topography of a region. [14]
5454	Control: Photogrammetric	Control established by photogrammetric methods, as distinguished from control established by ground methods. Also called minor control. [14]
5455	Coordinates: Plane Polar	The distance and direction from a central point of reference to a point whose position is being defined. The point of reference is termed the pole or origin; the line (distance) connecting the origin with the point whose position is being defined is the radius vector; and the angle between the fixed line (polar axis) which the direction is referred to and the radius vector is the vectorial angle. [14]
5456	Coordinates: Rectangular	Coordinates on any system in which the axes of reference intersect at right angles. [14]
5457	Correction: Relativistic	A correction for errors introduced by relativistic effects of the clock rates of positioning systems. [14]
5458	Declinational Inequality	See diurnal inequality. [14]
5459	Distance Finding Station	A radio beacon equipped with a synchronized sound signal to provide a means of determining distances from the source of the sound, by measuring the difference in the time of reception of the signals. [14]
5460	Double Meridian Distance	See meridian distance. [14]
5461	Equinoxes: Precession Of	See precession of the equinoxes. [14]
5462	Evaporation (Mixing) Fog	Fog produced when sufficient water vapor is added to the air by evaporation, and the moist air mixes with relatively drier air. The two common types are steam fog, which forms when cold air moves over warm water, and frontal fog, which forms as warm raindrops evaporate in a cool air mass. [1]
5463	Explosive Anchorage Area	An area set apart for anchored ships discharging or receiving explosives. [14]
5464	First Point Of Capricorn	See solstice. [14]
5465	Fish (Or Fishing) Stakes	Poles or stakes placed in shallow water to outline fishing grounds or to catch fish. [14]
5466	Focal Length: Calibrated	An adjusted value of the equivalent focal length computed to distribute the effect of lens distortion over the entire field used in an aerial camera. [14]
5467	Focal Length: Equivalent	The distance measured along the axis of lens from the rear nodal point to the plane of best average definition over the entire field used in an aerial camera. [14]
5468	Geographic(Al) Longitude	See longitude. [14]
5469	Gyroscopic Stabilization	Equilibrium in the attitude and/or course of a ship or airborne vehicle maintained by the use of gyroscopes. Also, the maintenance (by the use of gyroscopes) of a camera in a desired attitude within an airborne vehicle. [14]
5470	Height Of Eye Correction	See dip correction. [14]
5471	Higher Low Water (H.L.W)	The higher of two low waters occurring during a tidal day if diurnal inequality prevails. [14]
5472	Horizontal Control Datum	The position on the spheroid of reference assigned to the horizontal control (triangulation and traverse) of an area and defined by (1) the position (latitude and longitude) of one selected station in the area, and (2) the azimuth from the selected station to an adjoining station. See also datum: geodetic. [14]
5473	Interlines (Of Sounding)	Those sounding lines running between the normally spaced lines usually when the bottom is known or suspected to be irregular or if more detailed information about the sea bottom relief is required. [14]
5474	Isoclinal (Or Isoclinic)	(Adj.). Of or pertaining to equal magnetic dip. [14]
5475	Isotropic (Or Isotropus)	(Adj.). Having the same physical properties in all directions. [14]
5476	Latitude: Geographic(Al)	A general term, applying alike to astronomical and geodetic latitudes. [14]
5477	Length Correction (Tape)	See tape: length correction. [14]
5478	Levelling: Trigonometric	The determination of differences of elevations by means of observed vertical angles, combined with lengths of lines. [14]
5479	Lower Low Water (L.L.W.)	The lower of two low waters occurring during a tidal day if the diurnal inequality prevails. [14]
5480	Lower Low Water Interval	See lunitidal interval. [14]
5481	Lowest Astronomical Tide	The lowest tide level which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions. [14]
5482	Magnetic Field Intensity	The magnetic force exerted on a unit magnetic pole placed at any specified point of space. It is a vector quantity. Its direction is taken as the direction toward which a north magnetic pole would tend to move under the influence of the field. Also called magnetic intensity, magnetic field streng-th. [14]
5483	Marcq St. Hilaire Method	The establishing of a line of position from the observation of the altitude of a celestial body, and the calculation of its altitude and azimuth by the use of an assumed position. First introduced by Commandant Marcq St. Hilaire of the french navy. See intercept, sub-point. Also referred to as Saint Hilaire method or intercept method. [14]
5484	Mean High Water (M.H.W.)	The average height of all high waters at a place over a 19-year period. [14]
5485	Meridian: Geographic(Al)	A general term, applying alike to an astronomical or a geodetic meridian. [14]
5486	Multiple Lens Photograph	See photograph. [14]
5487	Narrow-Beam Echo Sounder	A sounder with a transducer of small aperture (typically 2° to 5°) required for high resolution mapping. [14]
5488	Navigational Observation	Observations necessary to fix the position of a vessel. [14]
5489	Nor'Easter (Northeaster)	A name given to a strong, steady wind from the northeast that is accompanied by rain and inclement weather. It often develops when a storm system moves northeastward along the coast of North America. [1]
5490	Observation(S): Magnetic	Measurement of any of the magnetic elements. [14]
5491	Oceanographic Slide Rule	A specially designed slide rule used for calculating the correction of thermal expansion of a deep sea reversing thermometer. [14]
5492	Parallel: Geographic(Al)	A line on the earth having the same latitude at every point. The term is applicable alike to an astronomical parallel or to a geodetic parallel. [14]
5493	Perigean Range (Of Tide)	The average of all monthly tide ranges occurring at the time of perigee. It is larger than the mean range, where the type of tide is either semidiurnal or mixed, and is of no practical significance where the type of tide is diurnal. [14]
5494	Photograph Perpendicular	The perpendicular from the interior perspective center to the plane of the photograph. [14]
5495	Photograph: High Oblique	An oblique photograph in which the apparent horizon is included within the field of view. [14]
5496	Polar Orbiting Satellite	A satellite whose orbit closely parallels the earth's meridian lines and thus crosses the polar regions on each orbit. [1]
5497	Position: Dead Reckoning	The position of a craft determined by dead reckoning, or by advancing a previous position for courses and distances. [14]
5498	Position: Geographic(Al)	The position of a point on the surface of the earth expressed in terms of latitude and longitude, either astronomical or geodetic. A sub-point. [14]
5499	Projection: Orthographic	A perspective azimuthal projection in which the projecting lines, emanating from a point at infinity, are perpendicular to a tangent plane. This projection is used chiefly in nautical astronomy for interconverting coordinates of the celestial equator and horizon systems. [14]
5500	Projection: Orthomorphic	See projection: conformal. [14]
5501	Radar Conspicuous Object	An object which returns a strong radar echo. [14]
5502	Raster Data Presentation	Method of digitally representing data of an image by a matrix-like scheme of pixels. [14]
5503	Recession Of A Shoreline	Landward movement of the shoreline. Also called retrogression of a beach. [14]
5504	Refraction: Astronomical	The apparent displacement of an object that results from light rays from a source outside the atmosphere being bent in passing the atmosphere. This results in all objects appearing to be higher above the horizon than they actually are. [14]
5505	Retired Line Of Position	A line of position which has been moved backward along the course line to correspond with a time previous to that at which the line was established. Called a transferred position line in British terminology. [14]
5506	Retrogression Of A Beach	See recession of a shoreline. [14]
5507	Sailing: Middle-Latitude	A method of converting departure into difference of longitude, or vice versa, when the true course is not 90° or 270°, by assuming that such a course is steered at the middle latitude. [14]
5508	Secondary Air Pollutants	Pollutants that form when a chemical reaction occurs between a primary air pollutant and some other component of air. Tropospheric ozone is a secondary air pollutant. [1]
5509	Sight (Or Sighting) Vane	See vane. [14]
5510	Single Beam Echo Sounder	(sbes) an echo sounder that transmits and receives a sound pulse providing a single spot depth, as opposed to a multi beam echo sounder. [14]
5511	Station Mark (Or Marker)	A buried mark-stone, a metal plug or disk, or any kind of permanent mark intended to provide a means of re-identifying main control stations. See surface mark and underground mark. [14]
5512	Stereographic Projection	See projection. [14]
5513	Subsurface Sound Channel	The submarine sound channel which is adjacent to the water surface. [14]
5514	Tape: Tension Correction	The correction applied to the nominal length of a tape to allow for a change in effective length because of its being used at a tension other than that for which its standard length is known. [14]
5515	Taut Wire Measuring Gear	An apparatus designed for measuring horizontal distances at sea. It is constructed so that a wire of small diameter, one end of which is anchored on the bottom, passes around a calibrated sheave as the ship steams along the route to be measured. [14]
5516	Tide(S): Quarter-Diurnal	The tide resulting from the distortion of the normal tide in shallow water with four high waters and four low waters during one day. See also tide(s): shallow water. [14]
5517	Tides: Mixed Semidiurnal	Semidiurnal tides with noticeable inequality in corresponding extremes. [14]
5518	Total Magnetic Intensity	The vector resultant of the intensity of the horizontal and vertical components of the earth's magnetic field at a specified point. [14]
5519	Trace (Of Precipitation)	An amount of precipitation less than 0.01 in. (0.025 cm). [1]
5520	Transverse Mercator Grid	The grid on a chart using the transverse Mercator projection. [14]
5521	Tropic Higher High Water	The higher high water of tropic tides. [14]
5522	Tropical Monsoon Climate	A tropical climate with a brief dry period of perhaps one or two months. [1]
5523	Vector Data Presentation	Method of representing image features digitally by points, lines and polygons given through their coordinates and appropriate code(s). [14]
5524	Very Low Frequency (Vlf)	See frequency: radio. [14]
5525	Wave: Transitional Water	A progressive gravity wave in water whose depth is less than 1/2 but more than 1/25 the wavelength. Often called shallow water wave. [14]
5526	Acoustic Line Of Position	See sonic line of position. [14]
5527	Aeronautical Ground Light	See light. [14]
5528	Age Of Diurnal Inequality	The time interval between the maximum semi-monthly north or south declination of the moon and the maximum effect of the declination upon the range of tide or the speed of the tidal current, this effect being manifested chiefly by an increase in the height or speed difference between the two high (low) waters or flood (ebb) currents during the day. The tides occurring at this time are called tropic tides. Also called diurnal age. [14]
5529	Astronomic(Al) Refraction	See refraction. [14]
5530	Base Course (Of A Vessel)	The true course between a vessel's point of departure and arrival. [14]
5531	Chart: Coast (Or Coastal)	A nautical chart intended for inshore coastwise navigation. [14]
5532	Circle Of Right Ascension	See hour circle. [14]
5533	Clamp (Or Clamping) Screw	A screw for holding in place a moving part of an instrument as during an observation or reading with a theodolite or sextant. [14]
5534	Coefficient Of Refraction	See refraction: coefficient of. [14]
5535	Contour (Or Contour Line)	A line connecting points of equal elevation or equal depth. See also form line, hachures, illuminated contours, index contours. [14]
5536	Datum Of Tide Predictions	The level from which the heights of tide are referenced in the tide tables. See also datum: chart. [14]
5537	Depression Of The Horizon	See dip. [14]
5538	Dispersion (Of Pollution)	The spreading out of atmospheric pollutants. [1]
5539	Dry (Or Dry Card) Compass	See compass. [14]
5540	Electronic Plotting Sheet	See plotting sheet. [14]
5541	Ellipticity Of An Ellipse	The ratio between the difference in length of the semi-axes of an ellipse and its semi-major axis. [14]
5542	Enhanced Group Call (Egc)	The system for broadcasting messages via the mobile satellite communications system operated by inmarsat. EGC is a part of the inmarsat-c system. [14]
5543	Error Of Magnetic Compass	The angle by which a compass direction differs from the true direction; the algebraic sum of variation and deviation. [14]
5544	Error Of Run (Micrometer)	The difference in seconds of arc, between the intended value of one turn of the micrometer screw and its actual value as determined by measuring the space between two adjacent graduation marks of the circle with the micrometer. Also called run of micrometer. [14]
5545	Establishment Of The Port	See establishment. [14]
5546	Extreme Water Level (Ewl)	Combination of design crest elevation, astronomical tide, and storm surge referenced to either lat or msl. [14]
5547	Final Great Circle Course	See course: great circle. [14]
5548	First Order Triangulation	See triangulation classification. [14]
5549	Fishery Conservation Zone	See fishing zone. [14]
5550	Frequency: Very Low (Vlf)	See frequency: radio. [14]
5551	Greenwich Mean Time (Gmt)	See time. [14]
5552	Halo: Large (Halo Of 46°)	Halo much less frequent and always less luminous than the small halo. It comprises a faintly luminous ring centered on the sun or moon and has an apparent radius of 46°. [14]
5553	Halo: Small (Halo Of 22°)	White, or mostly white, luminous ring of 22° radius with the luminary at its center. The small halo shows a faint red fringe on the inside and, in some rare cases, a violet fringe on the outside. The portion of the sky inside the ring is conspicuously darker than the rest of the sky. [14]
5554	Higher High Water (H.H.W)	The higher of two high waters occurring during a tidal day if the diurnal inequality prevails. [14]
5555	Higher Low Water Interval	See lunitidal interval. [14]
5556	Highest Astronomical Tide	The highest tidal level which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions. [14]
5557	Humid Continental Climate	A climate characterized by severe winters and mild to warm summers with adequate annual precipitation. Typically located over large continental areas in the northern hemisphere between about 40° and 70° latitude. [1]
5558	Humid Subtropical Climate	A climate characterized by hot muggy summers, cool to cold winters, and abundant precipitation throughout the year. [1]
5559	International (Int) Chart	A nautical chart with limits and scale in conformity with an internationally agreed scheme of such charts; carries the int number of that sheet; conforms to the chart specifications of the iho. [14]
5560	Isohaline (Or Isohalsine)	A line connecting points of equal salinity in the ocean. [14]
5561	Light (Or Lighted) Beacon	See beacon. [14]
5562	Light: Aerial Obstruction	Light marking an obstacle which constitutes a danger to air navigation. [14]
5563	Light: Fixed And Flashing	A rhythmic light in which a fixed light is combined with a flashing light of higher luminous intensity. [14]
5564	Longitude: Geographic(Al)	A general term, applying alike to astronomical and geodetic longitude. [14]
5565	Lower High Water (L.H.W.)	The lower of two high waters occurring during a tidal day if the diurnal inequality prevails. [14]
5566	Lower High Water Interval	See lunitidal interval. [14]
5567	Lubber (Or Lubber'S) Line	A reference line on any direction-indicating instrument, marking the reading which coincides with the heading. [14]
5568	Magnetic Annual Variation	The small systematic temporal variation in the earth's magnetic field which occurs after the trend for secular change has been removed from the average monthly values. Also referred to as annual variation. [14]
5569	Mandatory Routeing System	a routing system adopted by the international maritime organization, in accordance with the requirements of regulation v/10 of the 1974 solas convention, for mandatory use by all ships, certain categories of ships or ships carrying certain cargoes. [14]
5570	Meridian Distance: Double	The algebraic sum of the perpendicular distances from the two ends of any line of a traverse to the initial, or reference, meridian. [14]
5571	New Print Date (Of Chart)	In US Terminology, the date when a new print of a chart is issued which embodies changes or corrections of a relatively minor character. The new print date is added to the right of the edition date in the lower left-hand corner of the chart. [14]
5572	Obliquity Of The Ecliptic	The acute angle between the plane of the ecliptic and the plane of the celestial equator, about 23° 27'. [14]
5573	Ocean Acoustic Tomography	A method to determine the ocean structure based on precise measurements of transit time of acoustic waves between a net of transmitters and receivers. [14]
5574	Parallel Rulers (Or Rule)	An instrument for transferring a line parallel to itself. [14]
5575	Pelagic-Abyssal Sediments	Deep sea sediments that are free of terrestrial material except for a small proportion of very fine clay. [14]
5576	Photogrammetric Extension	See phototriangulation. [14]
5577	Photograph: Multiple Lens	A photograph made with a multiple lens camera. [14]
5578	Pingo-Like Features (Plf)	Small conical undersea features having the geomorphological appearance of pingos. [14]
5579	Plumb Line: Deflection Of	See deflection of the vertical. [14]
5580	Principal Vertical Circle	The vertical circle through the north and south points of the horizon, coinciding with the celestial meridian. [14]
5581	Reduction To The Meridian	The process of applying a correction to an altitude observed when a body is near the celestial meridian of the observer, to find the altitude at meridian transit. See altitude: ex-meridian. [14]
5582	Refraction Of Water Waves	The process by which the direction of a wave moving in shallow water at an angle to the contours is changed. That part of the wave advancing in shallower water moves more slowly than the other part still advancing in deeper water, causing the wave crest to bend toward alignment with the underwater contours. Also called wave refraction. The bending of wave crests by currents. [14]
5583	Route (Or Routeing) Chart	See chart. [14]
5584	Saturation Vapor Pressure	The maximum amount of water vapor necessary to keep moist air in equilibrium with a surface of pure water or ice. It represents the maximum amount of water vapor that the air can hold at any given temperature and pressure. (see equilibrium vapor pressure.) [1]
5585	Sea Bottom Sediment Chart	See chart: sea bottom sediment. [14]
5586	Separation Zone (Or Line)	A zone or line separating the traffic lanes in which ships are proceeding in opposite, or nearly opposite directions; or separating a traffic lane from the adjacent sea area; or separating traffic lanes designated for particular classes of ships proceeding in the same direction. [14]
5587	Shallow Water Corrections	Quantities to be applied to a tide prediction to correct for the quarter diurnal tides. [14]
5588	Shutter: Between-The-Lens	A shutter located between the lens elements of a camera; usually consisting of thin metal leaves which open and close or revolve to make the exposure. [14]
5589	Single Buoy Mooring (Sbm)	A large mooring buoy used by tankers to load and unload in port approaches or in offshore oil and gas fields. [14]
5590	Southern Oscillation (So)	The reversal of surface air pressure at opposite ends of the tropical pacific ocean that occur during major el niño events. [1]
5591	Stabilization: Gyroscopic	See gyroscopic stabilization. [14]
5592	Starred Lines Of Sounding	Lines of sounding which are 'starred' round a rock or islet. [14]
5593	Systems Of Sounding Lines	The predetermined lines that the survey platform is to follow for the best development of the depth contours in an area. [14]
5594	Tape: Catenary Correction	See tape: sag correction. [14]
5595	Telescope: Photo Zenithal	An instrument designed to take photos of stars culminating close to the zenith of a station in order to determine the position of the station with high accuracy. [14]
5596	Tension Correction (Tape)	See tape: tension correction. [14]
5597	Third Order Triangulation	See triangulation classification. [14]
5598	Transit: Broken Telescope	A precise astronomic transit or theodolite in which the light passing through the objective lens is reflected through a right angle by a prism placed in the horizontal axis. This hollow axis is continued beyond the supports, and the eyepiece is fitted at one end. [14]
5599	Underwater Photogrammetry	See photogrammetry. [14]
5600	Very High Frequency (Vhf)	See frequency: radio. [14]
5601	Visual Display Unit (Vdu)	See display. [14]
5602	Zero Crossing Wave Period	TZ ; The inverse of the average number of times that the ocean level moves up across the mean water level per second. [22]
5603	Age Of Parallax Inequality	The time interval between perigee of the moon and the maximum effect of parallax upon the range of tide or the speed of the tidal current. [14]
5604	Alignment Correction(Tape)	See tape: alignment correction. [14]
5605	Atomic Time: International	The time reference coordinate established by the bureau international de l'heure on the basis of atomic clocks. [14]
5606	Automatic Floating Station	A buoy equipped with instruments automatically recording oceanographic and meteorological data. Also called automatic buoy. [14]
5607	Beacon: Light (Or Lighted)	A beacon from which a light is exhibited. [14]
5608	Catenary Correction (Tape)	See tape: sag correction. [14]
5609	Celestial Line Of Position	A line of position determined by means of one celestial body. [14]
5610	Chart: Route (Or Routeing)	A chart showing routes between various places, usually with distances indicated. [14]
5611	Chart: Sea Bottom Sediment	A chart primarily showing information on the types and characteristics of sea bottom. [14]
5612	Clear Air Turbulence (Cat)	Turbulence encountered by aircraft flying through cloudless skies. Thermals, wind shear, and jet streams can each be a factor in producing cat. [1]
5613	Compass: Dry (Or Dry Card)	A compass without a liquid-filled bowl, particularly a magnetic compass having a very light compass card. Such a magnetic compass is seldom used in modern practice. See compass: liquid. [14]
5614	Compression (Of The Earth)	See flattening of the earth. [14]
5615	Continental Polar Air Mass	An air mass characterized by low temperatures and dry air. Not as cold as arctic air masses. [1]
5616	Cruising Radius (Or Range)	The distance a craft can travel at a given speed without refueling. [14]
5617	Daily Range Of Temperature	The difference between the maximum and minimum temperatures for any given day. [1]
5618	Draftsman (Or Draughtsman)	A person who makes drawings. [14]
5619	Electronic Data Processing	In a computer, data processing performed largely or exclusively on electronic equipment. [14]
5620	Enhanced Fujita (Ef) Scale	A modification of the original fujita scale that describes tornado intensity by observing damage caused by the tornado. [1]
5621	Equinoctial Spring Tide(S)	See tide. [14]
5622	Frequency: Very High (Vhf)	See frequency: radio. [14]
5623	Geographic(Al) Coordinates	See coordinates. [14]
5624	Higher High Water Interval	See lunitidal interval. [14]
5625	Intensity Of Magnetization	See magnetization. [14]
5626	Isothermal (Or Isothermic)	(Adj.). Of or relating to equal temperature. [14]
5627	Light: Aeronautical Ground	Any light specially provided as an aid to navigation, other than a light displayed on an aircraft. [14]
5628	Lighter Aboard Ship (Lash)	A cargo carrying system using specially built ships and lighters. Cargoes are loaded into lash lighters which are towed to a lash ship where they are embarked. At their destination the lash lighters are disembarked and towed away to their unloading berths. Special berths or anchorages are sometimes designated for lash ships. [14]
5629	Local Frequency Oscillator	An oscillator used to derive an intermediate frequency by beating with the signal carrying frequency in superheterodyne reception. [14]
5630	Local Magnetic Disturbance	An anomaly of the magnetic field of the earth, extending over a relatively small area, due to local magnetic influences. Also called local attraction or magnetic anomaly. [14]
5631	Magnetometric Zero Balance	A magnetic observatory instrument used for accurate measurement of the vertical component of the earth's magnetic field. [14]
5632	Maritime Tropical Air Mass	An air mass characterized by high temperatures and high humidity. [1]
5633	Metacentre (Or Metacenter)	That point in a floating body at which a vertical line drawn through its center of buoyancy when it is upright meets the vertical line drawn through its center of buoyancy when it is tipped. Centre of gravity of the unsubmerged part of a floating body; for stable equilibrium the meta center must be above the center of gravity. [14]
5634	Mountain And Valley Breeze	A local wind system of a mountain valley that blows downhill (mountain breeze) at night and uphill (valley breeze) during the day. [1]
5635	Occluded Front (Occlusion)	A complex frontal system that ideally forms when a cold front overtakes a warm front. When the air behind the front is colder than the air ahead of it, the front is called a cold occlusion. When the air behind the front is milder than the air ahead of it, it is called a warm occlusion. [1]
5636	Ocean Station Vessel (Osv)	Ship assigned to operate at the location of an ocean weather station. Also called weather ship. [14]
5637	Orientation Of Plane Table	Placing the plane table in such a position that every line drawn on the survey sheet from the point which represents the position of the table on the ground to any other point on the sheet, is parallel to the corresponding line in nature. [14]
5638	Parallel Motion Protractor	See protractor. [14]
5639	Plotting Sheet: Electronic	A chart showing time difference or phase difference curves of a circular or a hyperbolic navigational system. These lattice lines are used to accurately position the data collected during hydrographic or oceanographic surveys. [14]
5640	Potable Water Intake (Pwi)	A structure designed for the intake of drinking water. The intake is usually elevated above the bottom, supported and protected by a debris screening structure (crib), a separately charted feature. [14]
5641	Price-Gurley Current Meter	A battery powered electromechanical current meter which measures current speed only. [14]
5642	Radar Surveillance Station	A radar station established for traffic surveillance. [14]
5643	Radiant Energy (Radiation)	Energy propagated in the form of electromagnetic waves. These waves do not need molecules to propagate them, and in a vacuum they travel at nearly 300,000 km per sec (186,000 mi per sec). [1]
5644	Radio Navigational Warning	see navigational warning. [14]
5645	Refraction: Coefficient Of	The ratio of the angle of refraction at the point of observation to the angle at the center of the earth subtended by the arc connecting the point of observation and the observed point. [14]
5646	Second Order Triangulation	See triangulation classification. [14]
5647	Single Point Mooring (Spm)	A mooring structure used by tankers to load and unload in port approaches or in offshore oil and gas fields. The size of the structure can vary between a large mooring buoy and a manned floating structure. [14]
5648	Speed Of Relative Movement	See relative motion. [14]
5649	Super High Frequency (Shf)	See frequency: radio. [14]
5650	Supplemental Control Point	A photo image point for which an elevation or a horizontal position, or both, is to be, or has been determined. See also control point. [14]
5651	Tape: Alignment Correction	A correction applied to the measured length of a line to allow for the tape not being held exactly in a vertical plane containing the line. [14]
5652	Terrestrial Magnetic Field	See geomagnetic field. [14]
5653	Terrestrial Photogrammetry	See photogrammetry. [14]
5654	Tide (Or Tidal) Prediction	The mathematical process by which the times and heights of the tide are determined in advance from the harmonic constituents at a place. See harmonic analysis of tide. [14]
5655	Ultra High Frequency (Uhf)	See frequency: radio. [14]
5656	Ultraviolet (Uv) Radiation	Electromagnetic radiation with wavelengths longer than x-rays but shorter than visible light. [1]
5657	Underwater Sound Projector	A transducer used to produce sound in water. The conversion from electrical energy to sound is achieved through the use of either the piezoelectric or magneto strictive effect. See magnetostriction and piezoelectricity. [14]
5658	Universal Drafting Machine	See protractor: parallel motion. [14]
5659	Unsurveyed Clearance Depth	The estimated depth over an unsurveyed wreck or obstruction over which the exact depth is unknown but which is considered to have a safe clearance to the depth shown. [14]
5660	Visibility: Meteorological	The greatest distance at which a black object of suitable dimensions can be seen and recognized against the horizon sky, or, in the case of night observations, could be seen and recognized if the general illumination were raised to the normal daylight level. [14]
5661	Analogue Forecasting Method	A forecast made by comparison of past large-scale synoptic weather patterns that resemble a given (usually current) situation in its essential characteristics. [1]
5662	Annual Range Of Temperature	The difference between the warmest and coldest months at any given location. [1]
5663	Bathyscaphe (Or Bathyscaph)	A free, manned vehicle for exploring the deep ocean. [14]
5664	Continental Arctic Air Mass	An air mass characterized by extremely low temperatures and very dry air. [1]
5665	Coordinates: Geographic(Al)	A system of spherical coordinates for defining the positions of points on the earth. [14]
5666	Data Base Management System	A set of software for creating, maintaining and accessing the data of a data base. [14]
5667	Deep Scattering Layer (Dsl)	See phantom bottom. [14]
5668	Digital Terrain Model (Dtm)	A model representing the terrain surface by a collection of digital data, mainly coordinates in three dimensions, x, y, and z, and a digitally defined method to interpolate arbitrary terrain heights in between the stored values. Not to be confused with digital cartographic model which may also contain digital data representing terrain, but in a form suitable for the drawing of a particular kind of map. [14]
5669	Dilution Of Precision (Dop)	A parameter relating the precision of the position (and/or an unknown auxiliary) provided by a positioning system to that of the "observed quantities" directly measured by the system. Dop is a measure of the influence of the geometry of loci on the precision of position fixing. Dop is frequently used with a qualifying term such as geometric (gdop), horizontal (hdop), vertical (vdop) etc. To indicate that dop is related to all or some unknown quantities. [14]
5670	Electronic Line Of Position	A line of position established by means of electronic equipment. [14]
5671	Ellipticity Of The Spheroid	See flattening of the earth. [14]
5672	Error Of Closure Of Horizon	The amount by which the sum of a series of adjacent measured horizontal angels around a point fails to equal exactly 360°. [14]
5673	Exterior Perspective Centre	See perspective center. [14]
5674	Frequency: Super High (Shf)	See frequency: radio. [14]
5675	Frequency: Ultra High (Uhf)	See frequency: radio. [14]
5676	Horizon: Visible (Or Local)	See horizon: apparent. [14]
5677	Horizontal Force Instrument	See vibrating needle. [14]
5678	Hyperbolic Line Of Position	A line of position in the shape of a hyperbola, determined by measuring the difference in distance to two fixed points. [14]
5679	Incineration Areas (At Sea)	An offshore area officially designated as suitable for the burning of chemical waste by specially equipped ships. [14]
5680	Interior Perspective Centre	See perspective center. [14]
5681	International Nautical Mile	A unit of length equal to 1,852 meters. This value was approved by the international hydrographic conference of 1929 and has been adopted by nearly all maritime states. [14]
5682	Inverse Mercator Projection	See projection. [14]
5683	Light: Sector (Or Sectored)	A light presenting different appearances (in particular, different colors) over various parts of the horizon of interest to maritime navigation. [14]
5684	Liquid-In-Glass Thermometer	An instrument for measuring temperature. The most common is liquid-in-glass, which has a sealed glass tube attached to a glass bulb filled with liquid. See thermometer. [1]
5685	Longwaves In The Westerlies	A wave in the upper level of the westerlies characterized by a long length (thousands of kilometers) and significant amplitude. Also called Rossby waves. [1]
5686	Magnetic Temporal Variation	Any change in the earth's magnetic field which is a function of time. Also referred to as temporal variation. [14]
5687	Magnetostriction Transducer	See transducer. [14]
5688	Meteorological Observations	See observation. [14]
5689	Negative Feedback Mechanism	A process whereby an initial change in an atmospheric process will tend to either reinforce the process (positive feedback) or weaken the process (negative feedback). See feedback mechanism. [1]
5690	Niño/Southern Oscillation)"	A condition in the tropical pacific whereby the reversal of surface air pressure at opposite ends of the pacific ocean induces westerly winds, a strengthening of the equatorial countercurrent, and extensive ocean warming. [1]
5691	Oblique Plotting Instrument	An instrument (usually monocular) for plotting from oblique photographs. [14]
5692	Photogrammetry: Terrestrial	Photogrammetry utilizing terrestrial photographs. [14]
5693	Photographic Interpretation	The examination of photographic images for the purpose of identifying objects and deducing their significance. [14]
5694	Positive Feedback Mechanism	A process whereby an initial change in an atmospheric process will tend to either reinforce the process (positive feedback) or weaken the process (negative feedback). See feedback mechanism. [1]
5695	Precession Of The Equinoxes	The conical motion of the earth's axis about the vertical to the plane of the ecliptic, caused by the attractive force of the sun, moon, and other planets on the equatorial protuberance of the earth. [14]
5696	Protractor: Parallel Motion	An instrument consisting essentially of a protractor and one or more arms attached to a parallel motion device, so that the movement of the arms is everywhere parallel. The protractor can be rotated and set at any position so that it can be oriented to a chart. Also called universal drafting machine. [14]
5697	Roberts Radio Current Meter	An electro-mechanical current meter which measures current speed and direction. This meter can be suspended below an anchored buoy or ship which is equipped with a radio transmitter that transmits the current measurements to a ship or shore based monitor station. [14]
5698	Sensitivity Of Spirit Level	See sensibility of spirit level. [14]
5699	Sextant Altitude Correction	Any of several corrections applied to a sextant altitude in the process of converting it to true altitude. [14]
5700	Shelf Edge (Or Shelf Break)	The line along which there is a marked increase of slope at the seaward margin of a continental (or island) shelf. [14]
5701	Ship-To-Shore Triangulation	See triangulation. [14]
5702	Tachymeter (Or Tacheometer)	A surveying instrument designed for use in the rapid determination of distance, direction, and difference of elevation from a single observation, using a short base which may be an integral part of the instrument. [14]
5703	Tide(S): Equinoctial Spring	Those tides occurring near the equinoxes when the full or new moon and the sun have little or low declination and spring tides of greater range than the average occur, particularly if the moon is also nearly in perigee. [14]
5704	Tropic Low Water Inequality	See diurnal inequality. [14]
5705	Upper Limit Of Navigability	The character of a river will, at some point along its length, change from navigable to non navigable. Very often that point will be at a major fall or rapids, or other place where there is a marked decrease in the navigable capacity of the river. The upper limit will therefore often be the same point traditionally recognized as the head of navigation, but may, under some of the tests described above, be at some point yet farther upstream. [14]
5706	Absolutely Stable Atmosphere	An atmospheric condition that exists when the environmental lapse rate is less than the moist adiabatic rate. This results in a lifted parcel of air being colder than the air around it. [1]
5707	Adiabatic Temperature Change	Rise or fall of temperature due to compression or expansion without gain or loss of heat to the surroundings. [14]
5708	Base Extension Triangulation	(British terminology). A part of a triangulation net starting with a measured base and expanding that relatively short distance to a larger distance comparable to the average length of the triangulation sides. Called base net in US Terminology. [14]
5709	Cautionary (Or Caution) Note	Information calling special attention to some fact, usually a danger area shown on a chart, or other publication. [14]
5710	Centigrade Temperature Scale	See celsius temperature scale. [14]
5711	Circular Radiobeacon Station	A radio station which needs not necessarily be manned, the emissions of which, radiated around the horizon, enable its bearing to be determined by means of the radio direction finder of a ship. [14]
5712	Clearance: Overhead Pipeline	Minimum vertical or horizontal space available for passage. [14]
5713	Convergence Of The Meridians	The angular drawing together of the geographic meridians in passing from the equator to the poles. The difference between the two angles formed by the intersection of a great circle with two meridians. The difference between the reciprocal bearings of two points. At any point of a cartographic projection, the angle between the meridian, as represented on the plane of the projection and grid in use, and the grid north line. [14]
5714	Datum For Sounding Reduction	See datum: sounding. [14]
5715	Deflection Of The Plumb Line	See deflection of the vertical. [14]
5716	Fahrenheit Temperature Scale	A temperature scale defined by the relationship t°f = 1.8 t°c + 32; developed by Gabriel D. Fahrenheit (1686-1736), german physicist. [14]
5717	Interferometric Echo Sounder	A type of swath(e) sounding system in which the equipment emits a timed pulse of sound that is narrow in the fore-aft direction and wide in the across-track direction. The system samples the reflected sound hundreds or even thousands of times for each emission. For each sample, the phase difference of the reflected sound arriving at two (or more) receivers located a known distance apart is measured and used to compute the acoustic angle of arrival. Also, the time difference between the emission and reception for each sample is converted to a range. Geometry is then used to convert each range and angle to depths and also to position these depths within the swath(e) on the sea floor. [14]
5718	Köppen Classification System	A system for classifying climates developed by W. Köppen that is based mainly on annual and monthly averages of temperature and precipitation. [1]
5719	Light: Continuous Very Quick	A light showing 80 to 159, usually either 100 or 120, flashes per minute. [14]
5720	Mineral Development Platform	See platform: mineral development. [14]
5721	Napier'S (Or Napier) Diagram	A diagram on which compass deviation is plotted for various headings, and the points connected by a smooth curve, permitting a ready conversion of deviations from compass to magnetic headings, or vice versa. [14]
5722	Navigable Area Surveys (Nas)	Navigable area surveys are basic hydrographic surveys with restricted area coverage. The coverage is reduced by omitting requirements for: 1. Development of the 0 foot depth curve and foul, nearshore areas not considered navigable; 2. Complete field edit of the survey area. Navigable area surveys may also be restricted to the main navigable channel or corridor. [14]
5723	Observation Spot (Or Pillar)	A position ashore determined from celestial observations. [14]
5724	Observation(S): Astronomical	Observations of celestial bodies, with appropriate instruments. In navigation, the measurement of altitude and azimuth of celestial bodies. [14]
5725	Optical Pumping Magnetometer	See magnetometer. [14]
5726	Orientation: Photogrammetric	The recreation of natural terrain features at a miniature scale by the optical projection of overlapping photographs. The model is formed when all corresponding light rays from the two projectors intersect in space. See also orientation: absolute, orientation: basal, orientation: exterior, orientation: interior. [14]
5727	Projection: Inverse Mercator	The name given to the transverse Mercator projection when the latter is extended right over both poles. It is used for air charts of polar areas. [14]
5728	Radio Acoustic Sound Ranging	See radio acoustic ranging. [14]
5729	Rotating Radiobeacon Station	A special type of radio beacon station emitting a beam of waves to which a uniform turning movement is given, the bearing of the station being determined by means of an ordinary listening receiver and a stopwatch. Also referred to as rotating loop radio beacon. [14]
5730	Rubidium Vapour Magnetometer	See magnetometer. [14]
5731	Savonius Rotor Current Meter	A low-threshold current speed sensor composed of two cylindrical vanes disposed to form an s-shaped rotor responsive to a wide spectrum of horizontal flow components. [14]
5732	Scale Of Hydrographic Survey	That scale at which the positions of the soundings in the area are plotted on the hydrographic survey sheet. Suitable survey scales are selected in each case in accordance with the nature of the survey and the average depths prevailing in the area. [14]
5733	Tach Stave (Levelling Staff)	A staff with a length of about 2m with subdivisions. It is used in combination with a levelling instrument or theodolite. [14]
5734	Tape: Temperature Correction	The quantity applied to the nominal length of a tape to allow for a change in its effective length because of its being used at a temperature other than that for which its standard length is given. [14]
5735	Temperature-Salinity Diagram	The plot of temperature versus salinity data of a water column. The result is a diagram which identifies the water masses within the column, the column's stability, and indicates the ïƒt value, and allows an estimate of the accuracy of the temperature and salinity measurements. [14]
5736	Transducer: Magnetostriction	A transducer that depends for its operation on the interaction between the magnetization and the deformation of a material having magneto strictive properties. [14]
5737	Traverse: Open (Or Open End)	A traverse which starts from a station of known or adopted position but does not end upon such a station. Also called hanging traverse. [14]
5738	Triangulation Classification	The classifying of triangulations into first-order, second-order, and third-order triangulation, according to the error of closure of triangles. In first-order work, the average closure is not in excess of 1 second; in second order work, it does not exceed 3 seconds; and in third-order work, it does not exceed 5 seconds. For the basic first-order work, the computed length through the network must agree with the measured base within 1 part in 50 000, as a minimum, and average about 1 in 75 000, or better. [14]
5739	Triangulation: Ship-To-Shore	A method of triangulation involving simultaneous observations from three shore stations on a target carried by a ship offshore of the middle station. The middle station must be visible from each of the two end stations. [14]
5740	Tropic High Water Inequality	See diurnal inequality. [14]
5741	Tropical Wet-And-Dry Climate	A tropical climate poleward of the tropical wet climate where a distinct dry season occurs, often lasting for two months or more. [1]
5742	Vector Airborne Magnetometer	See magnetometer. [14]
5743	Vessel Traffic Service (Vts)	Any service implemented by a relevant authority primarily designed to improve safety and efficiency of traffic flow and the protection of the environment. It may range from simple information messages to extensive organization of the traffic involving national or regional schemes. [14]
5744	Astronomic(Al) Observation(S)	See observation. [14]
5745	Azimuth (Of A Celestial Body)	The angle between the observer's meridian and the vertical circle through the body, measured in the plane of the horizon. There is no universally accepted manner of reckoning the azimuths. Quadrantal, half-circle, and whole-circle methods are being used. In the latter, the azimuth is measured preferably clockwise from north. See also azimuth angle. [14]
5746	Bubble: Spirit (Or Sensitive)	See level: spirit. [14]
5747	Central Processing Unit (Cpu)	In computers in general the unit that comprises the arithmetic logic unit and the control unit. [14]
5748	Coherent Electromagnetic Wave	See wave: electromagnetic. [14]
5749	Collision-Coalescence Process	The process of producing precipitation by liquid particles (cloud droplets and raindrops) colliding and joining (coalescing). [1]
5750	Conic (Or Conical) Projection	see projection. [14]
5751	Continental (Or Island) Slope	The zone of declivity from the outer edge of a continental (or island) shelf into greater depth. See slope. [14]
5752	Continental Tropical Air Mass	An air mass characterized by high temperatures and low humidity. [1]
5753	Contrail (Condensation Trail)	A cloudlike streamer frequently seen forming behind aircraft flying in clear, cold, humid air. [1]
5754	Coring Instrument (Or Device)	See corer. [14]
5755	Electronic Navigation Station	See station. [14]
5756	Eulerian Current Observations	A method to monitor the current at a fixed point by means of current meters. [14]
5757	Fish Aggregating Device (Fad)	See fish haven. [14]
5758	Foot Of The Continental Slope	The point of maximum change of gradient at the base of the continental slope. [14]
5759	Frost (Also Called Hoarfrost)	A covering of ice produced by deposition on exposed surfaces when the air temperature falls below the frost point. [1]
5760	Geographic Information System	A computer-based system for handling and integrating data from a variety of sources which is directly or indirectly spatially referenced to earth. [14]
5761	Horizon System Of Coordinates	a set of celestial coordinates based on the celestial horizon as the primary great circle; usually altitude and azimuth or azimuth angle. [14]
5762	Hydrographic Data Acquisition	All on-site measurements to collect hydrographic data. [14]
5763	Isoclinal (Or Isoclinic) Line	A line connecting points of equal magnetic dip. Also called isoclinal. [14]
5764	Levelling Instrument: Y Level	A levelling instrument having the telescope, with attached spirit level, supported in y's. The telescope can be rotated about its longitudinal axis in the y's and it can be lifted and reversed, end for end. [14]
5765	Light: Continuous Ultra Quick	A light showing 160 or more, usually 240 to 300, flashes per minute. [14]
5766	Light: Interrupted Very Quick	A light in which the very rapid alterations of light and darkness are interrupted at regular intervals by eclipses of long duration. [14]
5767	Long Baseline Acoustic System	An underwater position fixing system which consists of an array of seabed transponders with baselines of several kilometers. [14]
5768	Low Water Quadrature (L.W.Q.)	The average low water interval when the moon is at quadrature. [14]
5769	Magnetometer: Optical Pumping	A highly sensitive magnetometer which employs a metastable helium or alkali metal absorption cell whose atoms absorb maximum energy from an infrared beam when a frequency modulation oscil-lator is tuned to its resonant frequency. The resonant frequency is proportional to the strength of the earth's magnetic field. [14]
5770	Magnetometer: Rubidium Vapour	An optical pumping magnetometer which employs a rubidium vapor absorption cell. [14]
5771	Magnetometer: Vector Airborne	A flux-gate magnetometer which measures the intensity and direction of the earth's magnetic field from an aircraft. [14]
5772	Phase Of A Navigational Light	A visually discrete part of a light signal. It is bounded by changes between darkness and light (e.g., An occultation or flash), or between different colors, or between distinctly different luminous intensities, and it may be further discriminated by its duration. [14]
5773	Plan Position Indicator (Ppi)	A cathode-ray scope on which signals appear in correct relation to each other, so that the scope face presents a map like representation of the area about the transmitter, the direction of a target being represented by the direction of its echo from a center and range by its distance from that center. [14]
5774	Plane Rectangular Coordinates	see coordinates. [14]
5775	Platform: Mineral Development	A platform used in the exploitation of minerals. [14]
5776	Polar Orthographic Projection	see projection. [14]
5777	Pressure Gradient Force (Pgf)	The force due to differences in pressure within the atmosphere that causes air to move and, hence, the wind to blow. It is directly proportional to the pressure gradient. [1]
5778	Profiling: Continuous Seismic	Determination of the subsoil strata and geological structure by use of sound sources which emit acoustic pulses to penetrate the seabed. Travel time between emission of pulses and reception is usually measured in a towed streamer. [14]
5779	Shortwave (In The Atmosphere)	A small wave that moves around long waves in the same direction as the air flow in the middle and upper troposphere. Shortwaves are also called shortwave troughs. [1]
5780	Standard Atmospheric Pressure	A pressure of 1013.25 millibars (mb), 29.92 inches of mercury (hg), 760 millimeters (mm) of mercury, 14.7 pounds per square inch (lb/in.2), or 1013.25 hectopascals (HPa). [1]
5781	Surveying (Or Mapping) Camera	See camera. [14]
5782	Synodic (Or Synodical) Period	The interval of time between any planetary configuration of a celestial body, with respect to the sun, and the next successive same configuration of that body, as from inferior conjunction to inferior conjunction. [14]
5783	Temperature Correction (Tape)	See tape: temperature correction. [14]
5784	Absolute Stereoscopic Parallax	See parallax. [14]
5785	Absolutely Unstable Atmosphere	An atmospheric condition that exists when the environmental lapse rate is greater than the dry adiabatic rate. This results in a lifted parcel of air being warmer than the air around it. [1]
5786	Calibration: Indirect Position	The calibration of a positioning system using positions of the survey vessel at different locations which were determined independently of the positioning system. True distances can be derived from these positions and by comparison with the data rendered by the positioning system, calibration values can be deduced. [14]
5787	Camera: Surveying (Or Mapping)	A camera specially designed for the production of photographs to be used in surveying. The prefix 'mapping' or 'surveying' indicates that the camera is equipped with means for maintaining and indicating the interior orientation of the photographs with sufficient accuracy for surveying purposes. A mapping camera may be an aerial mapping camera or a terrestrial mapping camera. [14]
5788	Coordinates: Plane Rectangular	A system of coordinates in a horizontal plane used to describe the positions of points with respect to an arbitrary origin by means of two distances perpendicular to each other. The two reference lines at right angles to each other passing through the origin are called the coordinate axes. The distances parallel to the true (or arbitrarily assigned) north-south axis are called the ordinates, or the y-coordinates. The distances parallel to the true (or arbitrarily assigned) east-west axis are called the abscissae, or the x-coordinates. The north and east directions are usually taken as positive, and the south and west directions are usually taken as negative. Also referred to as plane coordinates. [14]
5789	Digitization (Or Digitisation)	The process of converting analog data to digital data. [14]
5790	Direction Of Relative Movement	See relative motion. [14]
5791	Dry-Summer Subtropical Climate	A climate characterized by mild, wet winters and warm to hot, dry summers. Typically located between 30 and 45 degrees latitude on the western side of continents. Also called Mediterranean climate. [1]
5792	Ecliptic System Of Coordinates	A set of celestial coordinates based on the ecliptic as the primary great circle; celestial latitude and celestial longitude. [14]
5793	Equatorial Horizontal Parallax	See parallax. [14]
5794	Extremely High Frequency (Ehf)	See frequency: radio. [14]
5795	High Water Quadrature (H.W.Q.)	The average high water interval when the moon is at quadrature. See lunitidal interval. [14]
5796	Ice-Crystal (Bergeron) Process	A process that produces precipitation. The process involves tiny ice crystals in a supercooled cloud growing larger at the expense of the surrounding liquid droplets. Also called the bergeron process. [1]
5797	Initial Great Circle Direction	initial great circle course. [14]
5798	International Ice Patrol (Iip)	Activities of the international ice patrol include collecting and analyzing data concerning iceberg detection and movement. The patrol's mission is to provide the latest information on iceberg positions and computer prediction of the extent of the iceberg danger zone to North Atlantic mariners. Areas of study include iceberg detection, drift and deterioration, surface object drift, and currents in the grand banks region. [14]
5799	Light: Interrupted Ultra Quick	A light in which the ultra quick flashes (160 or more per minute) are interrupted at regular intervals by eclipses of long duration. [14]
5800	Light: Rotating (Or Revolving)	a light which has one or more beams which rotate. [14]
5801	Marginal Information (Or Data)	The notations printed in the margins or borders of mosaics, plans, or maps. [14]
5802	Maritime Boundary Delimitation	The process of establishing line(s) of delimitation at sea. [14]
5803	Microwave Distance Measurement	any method of electromagnetic distance measurement based on a comparison of radio microwave signals. [14]
5804	Observation(S): Meteorological	Evaluation or measurement of one or more meteorological elements. [14]
5805	Outlooks (Seasonal And 90-Day)	An overview or projection of how certain weather elements (such as temperature and precipitation) might compare with average weather conditions. [1]
5806	Projection: Conic (Or Conical)	a projection produced by projecting the geographic meridians and parallels onto a cone which is tangent to (or intersects) the surface of a sphere, and then developing the cone into a plane. [14]
5807	Projection: Polar Orthographic	an orthographic projection having the plane of the projection perpendicular to the axis of rotation of the earth (parallel with the plane of the equator); in this projection, the geographic meridians are straight lines. [14]
5808	Proton Precession Magnetometer	see magnetometer: nuclear precession. [14]
5809	Quartz Horizontal Magnetometer	see magnetometer. [14]
5810	Rock Which Covers And Uncovers	A rock of small area (pinnacle) that covers and uncovers at various states of the tide. [14]
5811	Short Baseline Acoustic System	An underwater acoustic position fixing system comprising a minimum of three hydrophones on the hull of a surface vessel. Three ranges are measured to a beacon either mounted on the seabed or a submersible to obtain a three-dimensional position fix. [14]
5812	Slotted-Template Triangulation	in photogrammetry, a graphical radial triangulation using slotted templates. [14]
5813	Station: Electronic Navigation	a station emitting radio signals which are used in electronic navigational systems. [14]
5814	Stereographic Polar Projection	see projection: stereographic. [14]
5815	Strip Film (Or Stripping Film)	A film which has the emulsion coated on an extremely thin membrane which is in turn supported on a normal ‘thickness film base. The emulsion and the membrane can be stripped (separated) from the base after exposure and processing. The thin image so obtained can be mounted face down on a new support for lateral image reversal or used for combining with, or inserting in, other image elements. [14]
5816	Synthetic Aperture Radar (Sar)	A radar with a synthetic aperture antenna which is composed of a large number of elementary transducing elements. The signals are electronically combined into a resulting signal equivalent to that of a single antenna of a given aperture in a given direction. [14]
5817	Transverse Mercator Projection	see projection. [14]
5818	Vertical Dilution Of Precision	See dilution of precision. [14]
5819	Wind Vector (Or Wind Velocity)	vector drawn in the sense and direction of the wind and of length proportional to wind speed. [14]
5820	Calibration: Indirect Variation	The calibration of a positioning system by obtaining redundant observations so that calibration values can be deduced mathematically from the discrepancies between uncalibrated values at different locations. [14]
5821	Direction Method Of Observation	A method of observing angular relationships wherein the graduated circle is held in a fixed position, and the directions of the various signals are observed around the horizon. Thus, directions are pointing whereby angles are found by the differences in direction. [14]
5822	Electromagnetic Position Fixing	Any process or technique of fixing which employs the properties of electromagnetic waves. [14]
5823	Estimated Time Of Arrival (Eta)	The predicted time of reaching a destination or waypoint. [14]
5824	Frequency: Extremely High (Ehf)	See frequency: radio. [14]
5825	Geometric Dilution Of Precision	See dilution of precision. [14]
5826	Global Positioning System (Gps)	a satellite-based navigation system designed to provide highly accurate position and velocity information in three dimensions and precise time and time interval on a global basis continuously. Gps is operated by the united states government. Gps to which differential corrections have been applied is known as differential gps (DGPS). See also global navigation satellite system. [14]
5827	Hydrographic Survey Examination	Review of a hydrographic survey that is directed toward evaluating compliance with, and the adequacy of, standards, rather than a careful examination of the data and their quality. The survey is carefully examined for adequacy with respect to data acquisition and conformance with applicable standards and project instructions. In addition, the overall condition of the records and the descriptive report are examined. The digital data representing the survey is plotted and subjected to a cursory examination (spot check) to ensure that digital data standards are being adhered to. The examination of the survey data is limited only to that necessary to evaluate the acquisition and processing procedures. [14]
5828	Lagrangian Current Observations	The method for observing ocean currents by tracking the movement of drifting floats, buoys, tracers etc. The rate and direction of movement of a particular sample of water is measured. This is the opposite to eularian current observations where the movement of water past a fixed point is measured by a current meter. [14]
5829	Light: Composite Group-Flashing	A flashing light in which a sequence of groups of one or more flashes, which are specified in number, is regularly repeated, and the groups comprise different numbers of flashes. [14]
5830	Light: Fixed And Group-Flashing	A fixed light varied at regular intervals by a group of two or more flashes of greater brilliance. This character is being gradually suppressed. [14]
5831	Magnetometer: Proton Precession	see magnetometer: nuclear precession. [14]
5832	Magnetometer: Quartz Horizontal	a magnetometer in which the torque exerted on a suspended magnet by the earth's horizontal magnetic field is balanced against the torque exerted by the quartz suspension fibre when twisted through 360°. [14]
5833	Mean Low Water Neaps (M.L.W.N.)	the average height of the low waters of neap tides. Also called neap low water. [14]
5834	Mean Lower Low Water (M.L.L.W.)	the average height of the lower low waters at a place over a 19-year period. [14]
5835	Nuclear Precession Magnetometer	see magnetometer. [14]
5836	Obliquity (Of The Earth'S Axis)	The tilt of the earth's axis. It represents the angle from the perpendicular to the plane of the earth's orbit. [1]
5837	Parallax: Absolute Stereoscopic	In photogrammetry, considering a pair of aerial photographs of equal principal distance, the algebraic difference of the distances of the two images from their respective photograph nadirs, measured in a horizontal plane and parallel to the air base. Also called horizontal parallax, linear parallax, or x-parallax. [14]
5838	Parallax: Equatorial Horizontal	horizontal parallax as observed at the equator, as it attains its maximum value. [14]
5839	Projection: Stereographic Polar	See projection: stereographic. [14]
5840	Remotely Operated Vehicle (Rov)	An unmanned submersible craft which can be used either for observation purposes or to perform hydrographic surveys, or for working purposes. Also called "remotely controlled vehicle (RCV)". [14]
5841	Sensibility Of Magnetic Compass	The ability of a magnetic compass card to align itself with the magnetic meridian after deflection. [14]
5842	Source Regions (For Air Masses)	Regions where air masses originate and acquire their properties of temperature and moisture. [1]
5843	Transhipment Or Lightening Area	An area designated for transfer of cargo from one vessel to another sometimes in order to reduce a vessel ™s draught. Also called cargo transfer area or cargo transshipment area. [14]
5844	Azimuthal Equidistant Projection	See projection. [14]
5845	Calibration: Direct Simultaneous	The calibration of a positioning system at the same time when the distances used for calibration are measured using another system or instrument of superior accuracy. [14]
5846	Common (Or Vulgar) Establishment	See establishment. [14]
5847	Compensation Of Magnetic Compass	The process of neutralizing or reducing to a minimum the magnetic effects the vessel itself exerts on a magnetic compass. It is based on the principle that the magnetic effect of the iron and steel of the vessel can be counterbalanced by means of magnets and soft iron placed near the compass. Also called compass adjustment, compass compensation, or magnetic compensation. [14]
5848	Coordinated Universal Time (Utc)	See universal time coordinated. [14]
5849	Cross Section Lines Of Soundings	Sounding lines run in a survey perpendicular to the flow of a stream and from bank to bank in a river. [14]
5850	Direction (Or Directional) Light	See light. [14]
5851	High Water Lunitidal Interval (H	.i.). See lunitidal interval. [14]
5852	Light: Composite Group-Occulting	An occulting light in which a sequence of groups of one or more eclipses, which are specified in number, is regularly repeated, and the groups comprise different numbers of eclipses. [14]
5853	Magnetometer: Nuclear Precession	a magnetometer that utilizes the precessional characteristics of hydrogen nuclei when in an ambient magnetic field. Also known as proton precession magnetometer. [14]
5854	Mean High Water Neaps (M.H.W.N.)	The average height of the high waters of neap tides. Also called neap high water. [14]
5855	North Atlantic Oscillation (Nao)	A reversal of atmospheric pressure over the atlantic ocean that influences the weather over Europe and over eastern North America. [1]
5856	Period (Of A Navigational Light)	The time taken to exhibit one complete sequence of intervals of light and darkness. [14]
5857	Repetition Method Of Observation	a method of observing horizontal angles by which the observations of each angle are completed separately. See theodolite: repeating. [14]
5858	Stereographic Horizon Projection	See projection: stereographic. [14]
5859	Stereoscopic Plotting Instrument	An instrument for compiling a map or obtaining spatial solutions by observation of stereoscopic images formed by stereoscopic pairs. See compilation. [14]
5860	System International (Si System)	System of metric measures consisting of seven basic units which are metre, kilogram, second, ampere, kelvin, mole and candela. [14]
5861	Thermometer: Protected Reversing	A reversing thermometer enclosed in a heavy glass case to protect it from hydrostatic pressure. [14]
5862	Universal Time Coordinated (Utc)	The time scale that is available from most broadcast time signals. It differs from international atomic time by an integral number of seconds. UTC is maintained within 1 second of ut1 by the introduction of 1-second steps (leap seconds) when necessary, normally at the end of December. Dut1, an approximation to the difference ut1 minus UTC, is transmitted in code on broadcast time signals. [14]
5863	Vulgar (Or Common) Establishment	see establishment. [14]
5864	Azimuthal Orthomorphic Projection	See projection: stereographic. [14]
5865	Barometer: Mercurial (Or Mercury)	A barometer in which atmospheric pressure is balanced against the pressure exerted by a column of mercury. [14]
5866	Chemical Weathering- Co2 Feedback	A negative feedback in earth's climate system. As chemical weathering of rocks increases, co2 is removed from the atmosphere more quickly, which in turn weakens the greenhouse effect, causing the atmosphere to cool. Thus, an increase in global chemical weathering tends to lower atmospheric temperatures. [1]
5867	Conditionally Unstable Atmosphere	An atmospheric condition that exists when the environmental lapse rate is less than the dry adiabatic rate but greater than the moist adiabatic rate. Also called conditional instability. [1]
5868	Dew Point (Dew-Point Temperature)	The temperature to which air must be cooled (at constant pressure and constant water vapor content) for saturation to occur. [1]
5869	Digital Imagery Processing System	A system which processes images which are stored in digital form. [14]
5870	Direction Of The Force Of Gravity	See gravity: direction of. [14]
5871	Estimated Time Of Departure (Etd)	The predicted time of leaving a place. [14]
5872	Levelling Instrument: Dumpy Level	A levelling instrument which has its telescope permanently attached to the levelling base, either rigidly or by a hinge that can be manipulated by a micrometer screw. [14]
5873	Light: Direction (Or Directional)	a light illuminating a sector of very narrow angle and intended to mark a direction to be followed. [14]
5874	Light: Interrupted Quick-Flashing	A quick light in which the sequence of flashes is interrupted by regularly repeated eclipses of constant and long duration. [14]
5875	Maritime Safety Information (Msi)	Navigational and meteorological warnings, meteorological forecasts, distress alerts and other urgent safety related messages broadcast to ships. [14]
5876	Mean Diurnal Low Water Inequality	See diurnal inequality. [14]
5877	Mean Higher High Water (M.H.H.W.)	The average height or higher high waters at a place over a 19-year period. [14]
5878	Mean Low Water Springs (M.L.W.S.)	The average height of the low waters of spring tides. This level is used as a tidal datum in some areas. Also called spring low water. [14]
5879	Navstar Global Positioning System	A satellite navigation system. [14]
5880	Pacific Decadal Oscillation (Pdo)	A reversal in ocean surface temperatures that occurs every 20 to 30 years over the northern pacific ocean. [1]
5881	Projection: Azimuthal Equidistant	an azimuthal projection on which straight lines radiating from the center or pole of projection represent great circles in their true azimuths from the center, and lengths along these lines are of exact scale. This projection is neither equal area nor conformal. [14]
5882	Punched (Or Punch) Card Equipment	A system whose principal feature is that numbers are recorded on cards by means of holes punched in successive columns of a card, the row of the card indicating the digit. [14]
5883	Radiative Equilibrium Temperature	The temperature achieved when an object, behaving as a blackbody, is absorbing and emitting radiation at equal rates. [1]
5884	Reference Spheroid (Or Ellipsoid)	A theoretical figure whose dimensions closely approach the dimensions of the geoid. The exact dimensions are determined by various considerations of the section of the earth's surface considered. The spheroids of bessel, clarke, delambre, everest, hayford, helbert and others have been adopted as reference spheroids in geodetic work by different countries. Also called spheroid of reference, or ellipsoid of reference. See also spheroid: oblate. [14]
5885	Rescue Co-Ordination Centre (Rcc)	A unit responsible for promoting efficient organization of search and rescue services and for coordinating the conduct of search and rescue operations within a search and rescue region. Also called maritime rescue co-ordination center (MRCC) and joint rescue co-ordination center (JRCC). [14]
5886	Simultaneous Comparison Of Depths	The comparison of echo sounding depths with simultaneous direct vertical measurements of depth. Simultaneous comparisons are periodically made to determine the instrumental error of echo sounders. [14]
5887	Unprotected Reversing Thermometer	See thermometer. [14]
5888	Volatile Organic Compounds (Vocs)	A class of organic compounds that are released into the atmosphere from sources such as motor vehicles, paints, and solvents. Vocs (which include hydrocarbons) contribute to the production of secondary pollutants, such as ozone. [1]
5889	Bearing: Mercatorial (Or Mercator)	See bearing: rhumb. [14]
5890	Covers And Uncovers (Or Discovers)	Expression intended to indicate an area of a reef or other projection from the bottom of a body of water which periodically extends above and is submerged below the surface. Also referred to as dries or uncovers. [14]
5891	Direction Of Movement Of The Waves	Direction from which the waves arrive at a fixed point. [14]
5892	Freezing Rain And Freezing Drizzle	Rain or drizzle that falls in liquid form and then freezes upon striking a cold object or ground. Both can produce a coating of ice on objects, which is called glaze. [1]
5893	Galvanoplasty (Or Galvanoplastics)	the process of coating things with metal by means of electrolysis. [14]
5894	Inclination Of The Horizontal Axis	The vertical angle between the horizontal axis of a surveying or astronomical instrument and the plane of the horizon. [14]
5895	Instrumental (Or Instrument) Error	See error. [14]
5896	Lambert Conformal Conic Projection	See projection. [14]
5897	Mean Diurnal High Water Inequality	See diurnal inequality. [14]
5898	Mean High Water Springs (M.H.W.S.)	The average height of the high waters of spring tides. Also called spring high water. [14]
5899	Meridional Orthographic Projection	See projection. [14]
5900	Mesoscale Convective Complex (Mcc)	A large organized convective weather system comprised of a number of individual thunderstorms. The size of an mcc can be 1000 times larger than an individual ordinary thunderstorm. [1]
5901	Meteorological Optical Range Table	A table from the international visibility code which gives the code number of meteorological visibility and the meteorological visibility for several weather conditions such as thin fog (code no. 4-meteorological visibility 1/2-1 nautical mile); clear (code no. 7-meteorological visibility 5 1/2-11 nautical miles). [14]
5902	Numerical Weather Prediction (Nwp)	Forecasting the weather based upon the solutions of mathematical equations by high-speed computers. [1]
5903	Polar Front Jet Stream (Polar Jet)	The jet stream that is associated with the polar front in middle and high latitudes. It is usually located at altitudes between 9 and 12 km. [1]
5904	Projection: Azimuthal Orthomorphic	see projection: stereographic. [14]
5905	Side-Looking Airborne Radar (Slar)	A radar system using a stabilized antenna orientated at right angles to the aircraft flight path. [14]
5906	Temperature Correction (Levelling)	That correction which is applied to an observed difference of elevation to correct for the error introduced when the temperature at which the levelling rods are used in the field is different from the temperature at which they were standardized. [14]
5907	Thermometer: Unprotected Reversing	A reversing thermometer which is not protected against hydrostatic pressure. Used in conjunction with protected reversing thermometers to determine thermometric depth. [14]
5908	Air Pressure (Atmospheric Pressure)	The pressure exerted by the mass of air above a given point, usually expressed in millibars (mb), inches of mercury (hg) or in hectopascals (HPa). [1]
5909	Air Pressure (Atmospheric Pressure)	The pressure exerted by the mass of air above a given point, usually expressed in millibars (mb), inches of mercury (hg) or in hectopascals (HPa). [1]
5910	Automatic Radar Plotting Aid (Arpa)	A system wherein radar targets are automatically acquired and tracked and collision situations computer assessed and warnings given. [14]
5911	Centimetre-Gram-Second (Cgs) System	The system of physical units in which the fundamental units of length, mass and time are the centimeter, gram and second, respectively. [14]
5912	Cold Advection (Cold Air Advection)	The transport of cold air by the wind from a region of lower temperatures to a region of higher temperature. [1]
5913	Eccentricity (Of The Earth'S Orbit)	The deviation of the earth's orbit from elliptical to nearly circular. [1]
5914	Electronic Navigational Chart (Enc)	1. An electronic navigational chart is a subset of the electronic chart data base held on the vessel. It contains information on features useful for navigation such as coastline, obstructions, beacons etc. 2. The digital data base that is intended to be used in conjunction with ECDIS. Standardized as to content, structure and format the enc may contain supplementary nautical information useful for safe navigation. The enc is a subset of the master data base of chart information. [14]
5915	Error: Instrumental (Or Instrument)	A systematic error resulting from imperfections in, or faulty adjustment of, instruments or devices used. [14]
5916	Hydrographic Airborne Laser Sounder	A system for measuring the depth of water by sending a laser pulse from an aircraft and recording the time difference between the sea surface and the bottom reflection. [14]
5917	Hydrographic Data Processing System	A system for verification, selection, and calculation of hydrographic survey data. [14]
5918	Hypsographic (Or Hypsometric) Curve	A curve used to indicate the proportion of the area of the surface at various elevations above or depths below a given datum. [14]
5919	Levelling Instrument: Tilting Level	A levelling instrument in which the final levelling of the instrument is obtained by small controlled amounts of rotation of the telescope about a horizontal axis. [14]
5920	Orientation Of Surveying Instrument	Placing the instrument in such position that the horizontal circle reads 0° when the line of collimation is parallel to the direction it had at an earlier (initial) position of the instrument, or to a standard line of reference. If the line of reference is a meridian, the circle will show azimuths referred to that meridian. [14]
5921	Projection: Azimuthal (Or Zenithal)	A projection on which the azimuths or directions of all lines radiating from a central point or pole are the same as the azimuths or directions of the corresponding lines on the sphere. [14]
5922	Projection: Lambert Conformal Conic	A conformal projection of the conical type, on which all geographic meridians are represented by straight lines which meet in a common point outside the limits of the map, and the geographic parallels are represented by a series of arcs of circles having this common point for a center. Meridians and parallels intersect at right angles, and angles on the earth are correctly represented on the projection. This projection may have one or two standard parallels along which the scale is held exact. [14]
5923	Projection: Meridional Orthographic	An orthographic projection having the plane of the projection parallel to the plane of some selected meridian; in this projection, the geographic parallels and the central meridian are straight lines, the outer meridian is a full circle, and the other meridians are arcs of ellipses. [14]
5924	Sensitivity Of Electronic Equipment	The ability of electronic equipment to amplify a signal, measured by the minimum strength of signal input capable of causing a desired value of output. The lower the input signal for a given output, the higher the sensitivity. [14]
5925	Stereographic Meridional Projection	See projection: stereographic. [14]
5926	Epicentre (Or Epicenter, Epicentrum)	The point of the earth's surface directly above the focus of an earthquake. [14]
5927	Intensity: Luminous (In A Direction)	Quotient of the luminous flux emitted by a source, or by an element of a source in an infinitesimal cone containing the given direction, by the solid angle of that cone. [14]
5928	International Ellipsoid Of Reference	A reference ellipsoid having the following approximate dimensions: semimajor axis 6378388.0 meters; semi minor axis 6356911.9 meters; and the flattening or ellipticity 1/297. See also Hayford's spheroid and flattening of the earth. [14]
5929	International Geophysical Year (Igy)	By international agreement, a period during which greatly increased observation of world-wide geophysical phenomena is undertaken through the cooperation effort of participating nations. [14]
5930	International Map Of The World (Imw)	The map of the world on the scale of 1/1 000 000 which was planned under the auspices of the international geographical union and carried out by very many of the countries of the world. [14]
5931	Irradiance (At A Point Of A Surface)	Quotient of the flux of radiation incident on an infinitesimal element of surface containing the point under consideration, by the area of that element. [14]
5932	Low Water Lunitidal Interval (L.W.I)	Low water interval. See lunitidal interval. [14]
5933	Projection: Stereographic Horizontal	See projection: stereographic. [14]
5934	Projection: Stereographic Meridional	See projection: stereographic. [14]
5935	Super-Short Baseline Acoustic System	A variation of the short baseline system with three sensors incorporated in a single transducer. [14]
5936	Astronomy: Nautical (Or Navigational)	Astronomy as applied to navigation. [14]
5937	Automatic Identification System (Ais)	an automatic communication and identification system intended to improve the safety of navigation by assisting the efficient operation of vessel traffic services (VTS), ship reporting, and ship-to-ship and ship-to-shore operations. [14]
5938	Ellipsoid Of Revolution (Or Rotation)	A simple mathematical surface which best approximates the shape of the earth. It is the surface generated by an ellipse revolving about one of its axes. See also spheroid: oblate, spheroid: prolate and reference spheroid. [14]
5939	General Circulation Of The Atmosphere	Large-scale atmospheric motions over the entire earth. [1]
5940	Instrumental (Or Instrument) Parallax	See parallax. [14]
5941	Intertropical Convergence Zone (Itcz)	The boundary zone separating the northeast trade winds of the northern hemisphere from the southeast trade winds of the southern hemisphere. [1]
5942	Irradiation (At A Point Of A Surface)	Product of an irradiance and its duration. [14]
5943	Magnetic Daily (Or Diurnal) Variation	Oscillations of the earth's magnetic field which have a periodicity of about a day and that depend to a close approximation only on local time and geographic latitude. [14]
5944	Parhelia Associated With The 22° Halo	Photometeor of the halo family, consisting of two luminous iridescent spots which appear on the parhelic circle close to the small halo. [14]
5945	Parhelia Associated With The 46° Halo	Photometeor of the halo family consisting of two luminous, iridescent spots which appear on the parhelic circle close to the large halo. [14]
5946	Position Dilution Of Precision (Pdop)	See dilution of precision. [14]
5947	Supercooled Cloud (Or Cloud Droplets)	A cloud composed of liquid droplets at temperatures below 0°c (32°f). When the cloud is on the ground it is called supercooled fog or cold fog. [1]
5948	Conditional Distribution (Probability)	Statistical distribution (probability) of the occurrence of a variable a, given that other variables b,c,… have certain assigned values. [14]
5949	Direction Of Traffic Flow: Established	A traffic flow pattern indicating the directional movement of traffic as established within a traffic separation scheme. [14]
5950	Direction Of Traffic Flow: Recommended	A traffic flow pattern indicating a recommended directional movement of traffic where it is impractical or unnecessary to adopt an established direction of traffic flow. [14]
5951	Illumination (At A Point Of A Surface)	Quotient of the luminous flux incident on an infinitesimal element of the surface containing the point under consideration, by the area of that element. [14]
5952	Insulated (Or Insulating) Water Bottle	See water bottle. [14]
5953	International Geographical Union (Igu)	Founded in 1922 to promote the study of geographical problems, igu initiates and coordinates research and provides for scientific discussion and publication. [14]
5954	Navigational (Or Navigation) Satellite	An artificial earth-orbiting satellite designed for navigational purposes. [14]
5955	Parallax: Instrumental (Or Instrument)	That change which may result from the position in which an observer stands with respect to the fiducial marks on an instrument (personal parallax); or by the imperfect adjustment of the optics of the instrument (optical parallax). [14]
5956	Particularly Sensitive Sea Area (Pssa)	An area which needs special protection through action by the IMO because of its significance for recognized ecological or socio-economic or scientific reasons and which may be vulnerable to damage by maritime activities. A PSSA is a type of environmentally sensitive sea area (ESSA). [14]
5957	Spectral Moment or nth Spectral Moment	Integral over frequency of the spectral density function multiplied by the nth power of the frequency, either expressed in hertz (cycles per second) or expressed in circular frequency (radians/second). [15]
5958	Survey (Or Surveying) Ship (Or Vessel)	A vessel or platform (e.g., Aircraft) specially equipped for carrying out topographic, hydrographic and/or oceanographic survey. [14]
5959	Warm Advection (Or Warm Air Advection)	The transport of warm air by the wind from a region of higher temperatures to a region of lower temperatures. [1]
5960	Water Vapor?Greenhouse Effect Feedback	A positive feedback whereby increasing surface air temperatures cause an increase in the evaporation of water from the oceans. Increasing concentrations of atmospheric water vapor enhance the greenhouse effect, which causes the surface air temperature to rise even more. [1]
5961	Analytical (Or Analytic) Photogrammetry	See under photogrammetry. [14]
5962	Celestial Equator System Of Coordinates	A set of celestial coordinates based on the celestial equator as the primary great circle. Usually declination, right ascension and hour angle, or sidereal hour angle. Also called equinoctial system of coordinates. [14]
5963	Echo Sounding Instrument (Or Apparatus)	See echo sounder. [14]
5964	Horizontal Dilution Of Precision (Hdop)	See dilution of precision. [14]
5965	Instrumental (Or Instrument) Correction	That correction due to instrumental error. [14]
5966	International Geological Congress (Igc)	Congresses held by IUGS. [14]
5967	International Hydrographic Bureau (Ihb)	Founded in 1921 in the Principality of Monaco, to establish a close and permanent association among the hydrographic offices of its member states; since 1970 the headquarters of the international hydrographic organization. [14]
5968	Large Automatic Navigation Buoy (Lanby)	A large buoy designed to take the place of a lightship where construction of an offshore light station is not feasible. See also buoy: super. [14]
5969	Satellite: Navigational (Or Navigation)	See navigational (or navigation) satellite. [14]
5970	Water Bottle: Insulated (Or Insulating)	A water bottle specially designed for measuring temperatures and collecting water samples at moderate depths. This type of water bottle is insulated to maintain the temperature constant while being brought to the surface. [14]
5971	World Meteorological Organization (Wmo)	Promotes international cooperation in the field of meteorology. [14]
5972	Azimuth: Astronomic(Al) Determination Of	The determination of the azimuth of a line or base line by astronomical observations. [14]
5973	Composite Electronic Navigational System	One contrived in such a way that the position is determined by lines of different types, for instance, by a lattice of circles and a lattice of hyperbolae. [14]
5974	Food And Agricultural Organization (Fao)	Aims at the improvement of the standard of living, especially of the rural population of third world countries, by increasing the production and improving the distribution of agricultural products. [14]
5975	Photogrammetry: Analytical (Or Analytic)	Photogrammetry in which solutions are obtained by mathematical means. [14]
5976	Universal Transverse Mercator (Utm) Grid	See grid. [14]
5977	Environmentally Sensitive Sea Area (Essa)	a generic term which is used to describe a wide range of areas, considered sensitive for a variety of environmental reasons. [14]
5978	Global Navigation Satellite System (Gnss)	the standard generic term for satellite navigation systems ("satnav") that provide autonomous geo-spatial positioning with global coverage. As of 2011, GPS and GLONASS are the only operational systems with new systems (for example the e.u's galileo and china's beidou) expected by 2020. [14]
5979	High Water Full And Change (H.W.F And C.)	See establishment. [14]
5980	International Maritime Organization (Imo)	A specialized agency of the united nations whose primary role is to develop and maintain a comprehensive regulatory framework for shipping. Its remit includes safety, environmental concerns, legal matters, technical co-operation, maritime security and the efficiency of shipping. Imo was formerly called the inter-governmental maritime consultative organization (IMCO). [14]
5981	Levelling Instrument: Self-Aligning Level	A level in which a sensitive prism element inside the telescope acts on the principle of the pendulum and ensures that the line of sight is horizontal, even if the axis of the telescope is several minutes out of the horizontal. [14]
5982	Low Water Full And Change (L.W.F. And C.)	The average interval of time between the transit (upper or lower) of the full or new moon and the next low water. [14]
5983	Mean Lower Low Water Springs (M.L.L.W.S.)	The average height of lower low water springs at a place. [14]
5984	Projection: Universal Transverse Mercator	See grid: Universal Transverse Mercator (UTM). [14]
5985	Straits Used For International Navigation	Geographically, a narrow passage between two land masses or islands or group of islands connecting two larger sea areas. [14]
5986	Electromagnetic Distance Measurement (Edm)	Any process or technique of distance measurement which depends on a comparison of signals by electromagnetic means. [14]
5987	International Association Of Geodesy (Iag)	One association of IUGG. [14]
5988	Electro-Optical Distance Measurement (Eodm)	Any method of electromagnetic distance measurement based on a comparison of light signals. [14]
5989	International Federation Of Surveyors (Fig)	Brings together the leading national associations to exchange views of general interest to the profession and organizes the liaison between the various affiliated associations. [14]
5990	International Scientific Radio Union (Isru)	Promotes and organizes international cooperative research in radio science. [14]
5991	Radio Direction Finding (Or Finder) Station	A radio station intended to determine only the direction of other stations by means of transmission from the latter. [14]
5992	United Nations Development Programme (Undp)	An un agency which registers organizations and institutions located in developing countries which have the capacity for cooperative technical activities with organizations in other developing nations. The subject matter includes education and training courses, research and technological development activities, consulting and expert services, and scientific and technical information and used primarily by institutions and governments in developing countries. [14]
5993	Character (Or Characteristics) Of The Bottom	See bottom: nature of. [14]
5994	International Cartographic Association (Ica)	Advances the study of cartographic problems; instigates cartographic research involving cooperation between nations. [14]
5995	International Telecommunications Union (Itu)	Maintains and extends international cooperation for the improvement and rational use of telecommunications. [14]
5996	Mean Low Water Lunitidal Interval (M.L.W.I.)	See lunitidal interval. [14]
5997	Precession (Of The Earth'S Axis Of Rotation)	The wobble of the earth's axis of rotation that traces out the path of a cone over a period of about 23,000 years. [1]
5998	Sensibility (Or Sensitivity) Of Spirit Level	The accuracy and precision which a spirit level is capable of producing. Sensibility depends on the radius of curvature of its longitudinal section; the longer the radius, the more sensitive the level. [14]
5999	Directional (Or Directed) Radiobeacon Station	A special type of radio beacon station the emissions of which are intended to provide a definite track for guidance. [14]
6000	Electronic Distance-Measuring Equipment (Edm)	Devices that measure the phase difference between transmitted and returned (i.e., Reflected or retransmitted) electromagnetic waves, of known frequency and speed, or the round-trip transit time of a pulsed signal, from which distance is computed. A wide range of such equipment is available for surveying and navigational use. Also called distance measuring equipment (DME). [14]
6001	International Hydrographic Organization (Iho)	Coordinates the activities of national hydrographic offices; promotes standards and provides advice to developing countries in the fields of hydrographic surveying and production of nautical charts and publications. [14]
6002	Marginal Distribution or Marginal Probability	Statistical distribution (probability) of the occurrence of a variable A that is obtained by integrating over all values of the other variables B, C, … NOTE The marginal probability of A for all values of B, C, … is written as P(A). The concept is applicable to metocean parameters, as well as to actions and action effects. EXAMPLE When considering wave conditions, A can be the individual crest elevation for all mean zero-crossing periods B and all significant wave heights C, occurring at a particular site. [15]
6003	Mean High Water Lunitidal Interval (M.H.W.I.)	See lunitidal interval. [14]
6004	Computer-Assisted (Computer-Aided) Cartography	A system which is used to perform specific cartographic function by means of computer hardware and software which aids humans to make decisions and/or perform their functions. Because of the graphic nature of cartography, such a system always contains, or makes use of, a computer graphics system. [14]
6005	Transverse Cylindrical Orthomorphic Projection	See projection: transverse Mercator. [14]
6006	General Bathymetric Chart Of The Oceans (Gebco)	A global series of small-scale bathymetric charts. Edited through international cooperation by IHO and IOC. [14]
6007	Projection: Transverse Cylindrical Orthomorphic	See projection: transverse Mercator. [14]
6008	Time: Greenwich Mean (Gmt) (Or Greenwich Civil)	Mean solar time at the Greenwich meridian. See universal time (ut). [14]
6009	World Wide Navigational Warning Service (Wwnws)	A service established for the purpose of coordinating the transmissions of radio navigational warnings in geographical areas using coastal and satellite communication services. [14]
6010	Intergovernmental Oceanographic Commission (Ioc)	Established within UNESCO to promote the scientific investigation of the oceans through the concerted action of member states. [14]
6011	Vertical Intensity Of The Earth'S Magnetic Field	The strength of the vertical component of the earth's magnetic field. [14]
6012	International Council Of Scientific Unions (Icsu)	Coordinates and facilitates activities of international scientific unions in the field of exact and natural sciences; maintains relations with the specialized and related agencies of the un. [14]
6013	International Union Of Geological Sciences (Iugs)	Contributes to the advancement of investigations relating to the study of the earth. [14]
6014	Luminance (At A Point Of Surface, In A Direction)	Quotient of the luminous intensity, in a given direction, of an infinitesimal element of the surface containing the point under consideration, by the orthogonally projected area of the element on a plane perpendicular to the given direction. [14]
6015	Scientific Committee On Antarctic Research (Scar)	A committee established by ICSU to promote and coordinate Antarctic research. [14]
6016	Global Maritime Distress And Safety System (Gmdss)	The gmdss is a global communications service based upon automated systems, both satellites based and terrestrial, to provide distress alerting and promulgation of maritime safety information for mariners. [14]
6017	Horizontal Intensity Of The Earth'S Magnetic Field	The strength of the horizontal component of the earth's magnetic field. [14]
6018	International Bureau Of Weights And Measures (Ibwm)	Establishment of international standards and of measurement scales of physical sizes; determination of fundamental physical constants. [14]
6019	International Indian Ocean Expedition (Iioe Or Ioe)	An international expedition between 1959 and 1965 under the general coordination of the IOC. [14]
6020	International Union Of Geodesy And Geophysics (Iugg)	Promotes the study of all problems relating to the configuration and physics of the earth, its oceans and atmosphere; comprises a number of international associations. [14]
6021	Electronic Chart Display And Information System (Ecdis)	The navigation information system which is considered the legal equivalent of the nautical chart, displaying selected information from an electronic navigation chart (enc) integrated with data from positional and, optionally, other sensors. [14]
6022	International Association For Hydraulic Research (Iahr)	Stimulates and promotes hydraulic research, both basic and applied, in all its aspects. [14]
6023	International Union Of Pure And Applied Physics (Iupap)	creates and encourages international cooperation in physics; secures international agreement on symbols, units, nomenclature, and standards. [14]
6024	Pan American Institute Of Geography And History (Paigh)	develops, coordinates, and disseminates geographical, cartographic, historical, geophysical and related scientific studies. [14]
6025	International Association Of Scientific Hydrology (Iash)	Promotes and develops the study of hydrology; initiates, facilitates and coordinates research on such hydrological problems requiring international cooperation. [14]
6026	Federation Of Astronomical And Geophysical Services (Fags)	Facilitates and promotes the collection of observations, information and statistics in the field of astronomical and geophysical sciences. The international time bureau is one of the services. [14]
6027	International Association Of Lighthouse Authorities (Iala)	Association of authorities responsible for the provision or maintenance of lighthouses and other aids to marine navigation. [14]
6028	International Council For The Exploration Of The Sea (Ices)	Promotes research and investigations for the study of the sea, particularly programs related to living resources. [14]
6029	United Nations Conference On Trade And Development (Unctad)	Helps to restructure patterns of international trade in order to enable developing countries to play their part in world commerce. [14]
6030	Organization For Economic Cooperation And Development (Oecd)	Member states promote economic growth, employment, and improved standards of living for a sound and harmonious development of world economy. [14]
6031	International Association Of Geomagnetism And Aeronomy (Iaga)	Promotes international coordination of efforts to further the sciences of geomagnetism and aeronomy. [14]
6032	Ordinary Cell Thunderstorm (Also Called Air-Mass Thunderstorm)	A thunderstorm produced by local convection within a conditionally unstable air mass. It often forms in a region of low wind shear and does not reach the intensity of a severe thunderstorm. [1]
6033	Spectral Density Function or Energy Density Function or Spectrum	Measure of the variance associated with a time-varying variable per unit frequency band and per unit directional sector NOTE 1 Spectrum is a shorthand expression for the full and formal name of spectral density function or energy density function. NOTE 2 The spectral density function is the variance (the mean square) of the time-varying variable concerned in each frequency band and directional sector. Therefore, the spectrum is in general written with two arguments: one for the frequency variable and one for a direction variable. NOTE 3 Within this document the concept of a spectrum applies to waves, wind turbulence and action effects (responses) that are caused by waves or wind turbulence. For waves, the spectrum is a measure of the energy traversing a given space. [15]
6034	International Association Of Theoretical And Applied Limnology (Ial)	Furthers the progress of theoretical and applied limnology by holding congresses, by publishing the proceedings of the congresses, and by providing a sound foundation of methods and techniques of limnological investigations. [14]
6035	Permanent International Association Of Navigation Congresses (Pianc)	Fosters progress of inland and maritime waterways, of ports and of coastal areas by research and information exchange. [14]
6036	International Association For The Physical Sciences Of The Ocean (Iapso)	Promotes the study of scientific problems relating to the ocean and interactions at its boundaries. [14]
6037	International Association Of Meteorology And Atmospheric Physics (Iamap)	promotes meteorological research and investigation including all aspects of atmospheric physics, particularly in those fields which require international cooperation. [14]
6038	International Cooperative Investigations Of The Tropical Atlantic (Icita)	an international expedition coordinated by the IOC. [14]
6039	United Nations Educational, Scientific, And Cultural Organization (Unesco)	Organized in 1945 to promote collaboration among nations in education, science, and culture; UNESCO is the parent agency for the intergovernmental oceanographic commission. [14]
6040	International Association Of Seismology And Physics Of The Earth'S Interior (Iaspei)	Develops the study of seismology and physics of the earth's interior in the economic, social and scientific aspects. [14]
6041	International Association Of Volcanology And Chemistry Of The Earth'S Interior (Iav)	Promotes research in all matters relating to volcanic activity; coordinates research in mineralogy, chemistry and physical chemistry for the benefit of volcanologists. [14]
6042	Moon	The satellite of the earth. See librations of moon and phases of the moon. [14]
6043	Duct	A layer in the ocean or atmosphere where refraction and, probably, reflection result in the trapping and propagation within the layer of sound waves or electromagnetic waves. [14]
6044	Latitude	Angular distance from a primary great circle or plane. One of the coordinates used to describe a position, the other being longitude. [14]
6045	Projection	The representation of a figure on a surface, either plane or curved, according to a definite plan. In a perspective projection this is done by means of projecting lines emanating from a single point, which may be infinity. In cartography, any systematic arrangement of meridians and parallels portraying the curved surface of the sphere or spheroid upon a plane. Also called map projection or chart projection. In photography, the reduction or enlargement of a positive or negative, by projecting the image through a lens. [14]
6046	Format	The general plan or arrangement of a product. Specification of succession and type of repre-sentation of elements of information (numbers, text) on a medium. A fixed format is equivalent to a table, while free formats use delimiters to separate individual elements or "tags" (based on a directory) to identify elements. A set of formats or a complex format determines the structure of how information is represented on a medium. [14]
6047	Bel	A dimensionless unit for expressing the ratio of two values of power, the number of bels being the logarithm to the base 10 of the power ratio. In practice decibel is commonly used, the number of decibels being 10 times the logarithm to the base 10 of the power ratio. [14]
6048	Set	(v.i.). Of a celestial body, to cross the apparent horizon while descending. The opposite is rise. To establish, as to set a course. [14]
6049	Set	The direction toward which a current flows. [14]
6050	Rock	Any formation of natural origin that constitutes an integral part of the lithosphere. The natural occurring material that forms the firm, hard, and solid masses of the ocean floor. An isolated rocky formation or a single large stone, usually one constituting a danger to navigation. See rock awash, sunken rocks, pinnacle and rock which covers and uncovers. [14]
6051	Parallel	A circle (or approximation of a circle) on the surface of the earth, parallel to the equator and connecting points of equal latitude. Also called parallel of latitude. [14]
6052	Coast	(v.t.). To sail along or near a coast. [14]
6053	Ordinate	See coordinates: plane rectangular. [14]
6054	Bit	Short for "binary digit", the digit in binary number representation. A bit can only assume the binary values "0" and "1". A binary number representation is composed of bits just as a decimal number is represented by decimal digits. A unit of 8 bits is called a byte. It also stands for "basic indissoluble information unit", a unit used for measuring the information content in information theory. [14]
6055	Day	The duration of one rotation of the earth, or occasionally another celestial body, on its axis. It is measured by successive transits of a reference point on the celestial sphere over the meridian, and each type takes its name from the reference used. The period of daylight, as distinguished from night. [14]
6056	Way	The motion of a vessel through the water. [14]
6057	Coast	The edge or margin of the land next to the sea; the seashore. Sometimes defined as the meeting of the land and sea considered as the boundary of the land. [14]
6058	Ping	An acoustic pulse signal projected by an underwater transducer. [14]
6059	Character	As pertains to typography, a graphic symbol such as a letter of the alphabet, figure, punctuation mark or sign employed in recording language. In data processing, an element of a code set used for representing information. [14]
6060	Marine	An adjective meaning relating to navigation or shipping; relating to or connected with the sea; used, or adopted for use at sea. Sometimes called maritime, but maritime is more frequently applied to that which borders on the sea. [14]
6061	Cove	A small bay. [14]
6062	Pole	Either of the two points of intersection of the surface of a sphere or spheroid and its axis. The origin of a system of polar coordinates. Either of the two magnetic poles of a magnet. A long slender rod, as of timber or metal. Such a rod used for sounding is called sounding pole. [14]
6063	Pond	A small body of still water of artificial formation, its bed being either hollowed out of the soil or formed by embanking and damming up a natural hollow. [14]
6064	Bar	A ridge or succession of ridges of sand or other substances extending across the mouth of a river or harbor and which may obstruct navigation. Derived pressure in the cgs system. See also millibar. [14]
6065	Lens	A plane, convex, or concave combination of glass or transparent material surfaces adapted for changing the direction of light rays to enlarge or reduce the apparent size of objects. See achromatic lens, apochromatic lens, anallactic lens, objective lens, eyepiece, lens element, lens system, magnifying glass. [14]
6066	Type	In printing (typography) a metal block having a raised letter or figure which, when inked, is used to make an impression on paper or other material. Type can also be in the form of negative or positive stripping film. [14]
6067	Zone	An area in all parts of which the same time is kept. In general, each zone is 15° of longitude in width, with the Greenwich meridian (0° longitude) designated as the central meridian of zone 0 and the remaining zones centered on a meridian whose longitude is exactly divisible by 15°. Zones are used in connection with zone, standard, and daylight saving times. Also called time zone. [14]
6068	Bed	The ground upon which a body of water rests. [14]
6069	Ray	A beam of radiant energy of infinitesimal cross-section, such as a light ray. [14]
6070	Flow	The motion characteristic of a fluid. [14]
6071	Rise	A broad elevation that rises gently and generally smoothly from the sea floor. [14]
6072	Cloud	Visible aggregate of minute particles of liquid water or ice, or of both together, in suspension in the atmosphere. This aggregate may include larger particles of liquid water or ice, non-aqueous particles or solid particles, originating for example from industrial gases, smoke or dust. [14]
6073	Datum	Any numerical or geometrical quantity or set of such quantities which may serve as a reference or base for other quantities. In geodesy a datum is defined by a set of parameters specifying the reference surface or the reference coordinate system. Therefore two types of datums are required: a horizontal datum which forms the basis for computations of horizontal control surveys in which the curvature of the earth is considered, and a vertical datum to which elevations are referred. [14]
6074	Scope	The face of a cathode-ray tube of electronic equipment. The various methods of presenting the information on a radar scope are usually designated by letter, as a-scope, b-scope, etc. Also called indicator, scan, screen, although the alphabetical designations are not generally used with screen. [14]
6075	Origin	In surveying, the reference position from which angles or distances are reckoned. See also coordinates: origin of. [14]
6076	Atmosphere	Gaseous envelope which surrounds the earth. The gaseous envelope surrounding any star, planet, etc. A unit of pressure, equal to the pressure exerted per square centimeter by a column of mercury 760 mm high at a temperature of 0°c when the acceleration of gravity is 980.665 centimeters per second squared.. [14]
6077	Rise	A broad elevation that rises gently and generally smoothly from the sea floor. [14]
6078	Stand	See stand of tide. [14]
6079	Plat	(US Terminology). A diagram drawn to scale showing land boundaries and subdivisions, and identification of the several units shown thereon, and including one or more certificates indicating due approval. A plat differs from a map in that it does not necessarily show additional cultural, drainage and relief features. See also map: cadastral. [14]
6080	Photogram	A survey photograph. Either of a pair of stereoscopic photographs. [14]
6081	Layer	A single thickness, coat, fold or stratum. [14]
6082	Bearing	The horizontal direction of one terrestrial point from another, expressed as the angular distance from a reference direction. It is usually measured from 0° at the reference direction clockwise through 360°. The terms bearing and azimuth are sometimes used interchangeably, but in navigation the former customarily applies to terrestrial objects and the latter to the direction of a point on the celestial sphere from a point on the earth. A bearing is designated as true, magnetic, or compass as the reference direction is true, magnetic, or compass north. [14]
6083	Equator	The primary great circle of a sphere or spheroid such as the earth, perpendicular to the polar axis. [14]
6084	Cap	A feature with a rounded cap-like top. [14]
6085	Camera	A lightproof chamber or box in which the images of exterior objects are projected upon a sensitized plate or film, through an opening usually equipped with a lens or lenses, shutter and variable aperture. [14]
6086	Elevation	(1) the vertical distance of a point or a level, on the surface of the earth, measured from a specified vertical datum usually mean sea level. The term elevation is sometimes confused with altitude. For paper nautical charts, this term is often synonymous with height. (2) for navigational lights, such as lighthouses, the vertical distance of the focal point of the light measured from a specified vertical datum. (3) an area higher than its surroundings, as a hill. [14]
6087	Star	Celestial bodies which appear as points of light due to their great distance from the earth. They are self ‘luminous whereas planets shine only by reflection light. [14]
6088	Float	Any buoyant object attached to nets or fishing lines: term also used for the small buoys used for current observations. [14]
6089	Frequency	The number of vibrations or cycles in unit time. [14]
6090	Storm	Wind with a speed between 44 and 50 knots (beaufort scale wind force 10). Note: the term 'storm' has been substituted for the term 'whole gale' in US Weather bureau warnings. This term refers to wind speeds of 48-63 knots. [14]
6091	Stream	(v.t.). To place overboard and secure, as to stream a log, or stream a sea anchor. [14]
6092	Correction	A quantity which is applied to an observation or function thereof, to diminish or eliminate the effects of errors and obtain an improved value of the observation or function. It is also applied to reduce an observation to some arbitrary standard. The correction corresponding to a given error is of the same magnitude but of opposite sign. See chronometer correction, dip correction, index correction, instrumental correction, lead line correction, parallax correction, personal correction, polaris correction, refraction correction, semidiameter correction, sextant altitude correction, sky wave correction, orthometric correction, tidal difference. [14]
6093	Meteor	Phenomenon other than a cloud, observed in the atmosphere or on the surface of the earth, which consists of a precipitation, a suspension or a deposit of aqueous or non-aqueous liquid or solid particles, or a phenomenon of the nature of an optical or electrical manifestation. [14]
6094	Stream	Any river, brook, rivulet or course of running water. A steady current in the sea or in a river, especially the middle or most rapid part of a tide or current. A steady flow of a fluid, small solid particles, or radiant energy. [14]
6095	Head	A precipitous cape, or promontory. See also headland. That part of a rip current that has widened out seaward of the breakers. [14]
6096	Course	The intended horizontal direction of travel. It is measured from 0° at the reference direction clockwise through 360°; strictly for marine navigation, the term applies to the direction to be steered, which sometimes differs from the direction intended to be made good over the ground (see drift angle). The course is designated as true, magnetic, compass, or grid as the reference direction is true, magnetic, compass or grid north respectively. See course made good and track. The channel in which water flows. See also watercourse. [14]
6097	Section	Process of locating and coordinating a point from at least two existing control stations by observing horizontal directions from the control stations to the point. Also called intersection. [14]
6098	Altitude	The vertical distance of a level, a point or an object considered as a point (but not affixed to the surface of the earth), measured from a given datum, usually mean sea level. See also elevation and height.- 2. In astronomy, the vertical angle between the plane of the horizon and the line to a celestial body. See also angle of depression and angle of elevation. [14]
6099	Variation	The angle between the magnetic and geographical meridians at any place, expressed in degrees east or west to indicate the direction of magnetic north from true north. Also called magnetic variation, or magnetic declination. [14]
6100	Hydrograph	Used in oceanography. The tidal current vector hydrograph is the figure traced out by the tip of a vector representing the current over the tidal cycle. [14]
6101	Coordinates	Linear or angular quantities which designate the position of a point in relation to a given reference system. [14]
6102	Normal	In general, a straight line perpendicular to a surface or to another line. In geodesy, a straight line perpendicular to the surface of the spheroid. [14]
6103	Hour	A 24th part of a day. [14]
6104	Measurement	The (detailed) dimensions of a physical quantity. [14]
6105	Source	The point where a river rises. [14]
6106	Azimuth	A horizontal angle reckoned clockwise from the meridian. The horizontal direction of a celestial point from a terrestrial point, expressed as the angular distance from a reference direction. It is usually measured from 000° at the reference direction clockwise through 360°. An azimuth is often designated as true, magnetic, compass, grid, or relative as the reference direction is true, magnetic, compass, or grid north, or heading, respectively. Unless otherwise specified, the term is generally understood to apply to true azimuth which may be further defined as the arc of the horizon, or the angle at the zenith, between the north part of the celestial meridian or principal vertical circle and a vertical circle, measured from 000° at the north part of the principal vertical circle clockwise through 360°. When the angle is measured in either direction from north or south, and labelled accordingly, it is properly called azimuth angle; when measured either direction from east or west, and labeled accordingly, it is called amplitude. [14]
6107	Weather	Adj.). Of or pertaining to the direction from which the wind is blowing, as opposed to lee. [14]
6108	Weather	State of the atmosphere at a given time, as defined by the various meteorological elements. [14]
6109	Structure	The term "structure" shall include, without limitation, any pier, wharf, dolphin, weir, boom, breakwater, bulkhead, revetment, riprap, jetty, permanent mooring structure, power transmission line, permanently moored floating vessel, piling, aid to navigation, or any other obstacle or obstruction. [14]
6110	Rain	Precipitation of liquid water particles in the form of drops of more than 0.5 mm diameter or of smaller widely scattered drops. [14]
6111	Nautical	(Adj.). Of or pertaining to ships, navigation (chiefly marine) or seamen. In contrast, navigational refers to navigation only. [14]
6112	Deep	In oceanography, an obsolete term which was generally restricted to depths greater than 6,000 m. An unmarked fathom point on a lead line. [14]
6113	Radar	A method, system or technique of using beamed, reflected, and timed radio waves for detecting, locating, or tracking objects, and for measuring altitudes. The electronic equipment or apparatus used to generate, transmit, receive, and usually, to display radio scanning or locating waves; a radar set. The name 'radar' is derived from the words radio detecting and ranging. [14]
6114	Plot	(v.t.). To draw lines and points to represent certain conditions graphically, as the various lines and points on a chart or plotting sheet, representing the progress of a craft, a graphical solution of a problem, etc. [14]
6115	Print	In photography, a copy made from a transparency by photographic means. [14]
6116	Year	A period of one revolution of the earth around the sun. [14]
6117	Solid	Matter of stable shape, not liquid or fluid. [14]
6118	Triangulation	A method of surveying in which the stations are points on the ground at the vertices of a chain or network of triangles. The angles of the triangles are measured instrumentally and the sides are derived by computation from selected triangle sides called bases (or base lines), the lengths of which are obtained from direct measurements on the ground. [14]
6119	River	A relatively large natural stream of water. [14]
6120	Atmospheric	Electromagnetic wave resulting from an electric discharge (lightning) in the atmosphere. [14]
6121	Photogrammetry	The science or art of obtaining reliable measurements from photographs. [14]
6122	Cycle	One complete series of events or phenomena that recur regularly in the same sequence. See also frequency, hertz, period. [14]
6123	Theodolite	A precision surveying instrument consisting of an alidade with a telescope. It is mounted on an accurately graduated circle and is equipped with necessary levels and reading devices. Sometimes, the alidade carries a graduated vertical circle. [14]
6124	Plotting	See plot. [14]
6125	Micrometer	An auxiliary device to provide measurement of very small angles or dimensions, by an instrument such as a telescope. See micrometer: filar, micrometer: transit. [14]
6126	Environment	The sum total of all external conditions which may affect an organism, community, material, or energy if brought under the influence of these external conditions. [14]
6127	Wave Length	The distance between corresponding points of two successive periodic waves in the direction of propagation, for which the oscillation has the same phase. Unit of measurement in meters. Also written as one word. [14]
6128	Revolution	Motion of a celestial body in its orbit; circular motion about an axis usually external to the body. The terms revolution and rotation are often used interchangeably but, with reference to the motions of a celestial body, revolution refers to the motion in an orbit or about an axis external to the body, while rotation refers to motion about an axis within the body. Thus, the earth revolves about the sun annually and rotates about its axis daily. [14]
6129	Echo Sounder	An instrument for determining the depth of water by measuring the time interval between the emission of a sonic or ultrasonic signal and the return of its echo from the bottom. Also called echo sounding instrument (or apparatus), sonic depth finder, or ultrasonic depth finder, as appropriate. See also sub-bottom profiler, swath(e) sounding system. [14]
6130	Radiobeacon	A radio transmitter which emits a distinctive or characteristic signal used for the determination of bearings, courses or location. One intended to mark a specific location is called marker beacon. [14]
6131	Transmitter	One who or that which transmits or sends anything, particularly a radio transmitter. [14]
6132	Wave Height	The vertical distance between a wave crest and the preceding wave trough. [14]
6133	Acceleration	The rate of change of velocity. [14]
6134	Tropic Tide	See tide. [14]
6135	Diurnal Tide	See tide. [14]
6136	Flood Stream	The horizontal movement of water associated with the rising tide. Flood streams generally set toward the shore, or in the direction of the tide progression. Also called flood, flood current or ingoing stream. [14]
6137	Reproduction	In cartography, the processes involved in printing copies from an original drawing. The principal processes are photography, lithography (or engraving), and printing. A printed copy of an original drawing, made by any of the processes of reproduction. [14]
6138	Sound Signal	Any sound produced to convey intelligence, as a fog signal. [14]
6139	Small Scale	See scale. [14]
6140	Axis Of Lens	The straight line which passes through the centers of curvature of the lens surfaces. Also called principal axis, optical axis or lens axis. [14]
6141	Gravity Wave	See wave. [14]
6142	Smooth Sheet	(US Terminology). See fair chart. [14]
6143	Spring Tides	Tides of increased range or tidal currents of increased speed occurring semimonthly as the result of the Moon being new or full. The spring range (Sg) of tide is the average range occurring at the time of spring tides and is most conveniently computed from the harmonic constants. It is larger than the mean range where the type of tide is either semi diurnal or mixed, and is of no practical significance where the type of tide is predominantly diurnal. The average height of the high waters of the spring tides is called spring high water or mean high water springs (MHWS) and the average height of the corresponding low waters is called spring low water or mean low water springs (MLWS). [22]
6144	Water Depth	Vertical distance between the sea floor and still water level. NOTE 1 As there are several options for the still water level (see Still Water Level), there can be several water depth values. Generally, design water depth is determined to LAT or to mean sea level. NOTE 2 The water depth used for calculating wave kinematics varies between the maximum water depth of the highest astronomical (HAT) tide plus a positive storm surge, and the minimum water depth of the lowest astronomical (LAT) tide less a negative storm surge, where applicable. The same maximum and minimum water depths are applicable to bottom founded and floating structures, although water depth is usually a much less important parameter for floating structures. Water depth is, however, important for the design and analysis of the mooring system and risers for floating structures. [15]
6145	Compass Card	That part of a compass on which the direction graduations are placed. Also referred to as card. [14]
6146	Datum: Chart	A permanently established surface from which soundings or tide heights are referenced, usually low water. Also called datum, datum level, datum plane, hydrographic datum, reference level, reference plane. See datum: tidal. [14]
6147	Magnetic Dip	See dip. [14]
6148	Surface Mark	A station mark used in addition to the underground mark, over which it is plumbed. [14]
6149	Tidal Stream	See current: tidal. [14]
6150	Upper Branch	That half of a meridian or celestial meridian from pole to pole which passes through a place or its zenith. [14]
6151	Wave Period	The time, in seconds, required for a wave crest to traverse a distance equal to one wavelength. [14]
6152	Bar Sweeping	A sweeping procedure using a beam suspended horizontally under a vessel. The sweep passing over the bottom may be equipped with rockers or other sensors to record contact with the bottom. [14]
6153	Bermuda High	A semipermanent high in the subtropical high-pressure belt centered near 30° latitude. The bermuda high is located over the Atlantic Ocean off the east coast of North America. The pacific high is located off the west coast of North America. See subtropical high. [1]
6154	Carrier Wave	See wave. [14]
6155	Circle Sheet	(US Terminology). A boat sheet or a smooth sheet on which intersecting systems of curves are drawn, each curve corresponding to the locus of some angle between two stations. Positions are plotted on circle sheets at the intersection of the loci of two observed angles, each locus being found by interpolation between the curves drawn on the sheet. Circle sheets are prepared and employed in hydrographic surveys for plotting fixes without the use of protractor. Also called standard circle sheet; formerly called sextant chart. See also fixed angle plot, and lattice. [14]
6156	Delimitation	The process of establishing the line(s) of delimitation in the context of the united nations' law of the sea convention. [14]
6157	Eccentricity	The amount of deviation from a center. [14]
6158	Geomagnetism	The magnetism of the earth. Also called terrestrial magnetism. [14]
6159	Ground Speed	In air navigation, the rate of motion of an aircraft along its track with relation to the ground. See also air speed. [14]
6160	Leading Line	(British terminology). A line passing through two or more clearly defined charted objects, and along which a vessel can approach safely. [14]
6161	Lens Element	One lens of a complex lens system. [14]
6162	Orthomorphic	(Adj.). Preserving the correct shape; of a projection which gives no local distortion. See projection: conformal. [14]
6163	Parallax: Y-	In photogrammetry, the difference between the perpendicular distances of the two images of a point on a pair of photographs from the vertical plane containing the air base. The existence of y-parallax is an indication of tilt in either or both photographs and/or a difference in flight heights, and interferes with stereoscopic examination of the pair. Also called vertical parallax or want of correspondence. [14]
6164	Small Circle	See circle. [14]
6165	Spring Range	The mean semidiurnal range of tide when spring tides are occurring. The mean difference in height between mean high water springs and mean low water springs. Also called mean spring range. [14]
6166	Traffic Lane	An area within defined limits in which one-way traffic is established. Natural obstacles, including those forming separation zones, may constitute a boundary. [14]
6167	Time Signal	See signal. [14]
6168	Arid Climate	An extremely dry climate, drier than the semi-arid climate. Often referred to as a true desert climate. [1]
6169	Atomic Clock	See clock. [14]
6170	Cloud Amount	The fraction of the sky covered by the clouds of a certain genus, certain species, certain variety, certain layer, or of a certain combination of clouds. Also called partial cloud amount. See cloud genera. [14]
6171	Compass Rose	A circle graduated in degrees clockwise from 0° (north) to 360° printed on a chart for use as a protractor. Compass roses are also placed at other convenient locations to facilitate measurements of directions. They may be oriented to the true or the magnetic north. [14]
6172	Conformality	The special property of conformal projection, i.e. That of having correct relationship about a point. [14]
6173	Cotidal Line	A line on a chart passing through all points where high water occurs at the same time. [14]
6174	Cumulonimbus	An exceptionally dense and vertically developed cloud, often with a top in the shape of an anvil. The cloud is frequently accompanied by heavy showers, lightning, thunder, and sometimes hail. It is also known as a thunderstorm cloud. [1]
6175	Depth Finder	An instrument for the measurement of the depth of water, particularly an echo sounder. [14]
6176	Ebb Interval	Short for strength of ebb interval. The interval between the transit of the moon over the meridian of a place and the time of the following strength of ebb. [14]
6177	Ekman Spiral	Spiral, polar diagram of the extremities of the wind vectors at different heights, representing the variation of the wind with height in the friction layer on the basis of various simplifying assumptions. The ekman spiral is also applied to the variation of wind-driven ocean currents with depth below the surface. [14]
6178	Fishing Zone	The offshore zone in which exclusive fishing rights and management are held by the coastal nation. [14]
6179	Fluorescence	Emission of light or other radiant energy as a result of and only during absorption of radiation from some other source. See luminescence and phosphorescence. [14]
6180	Fujita Scale	A scale developed by t. Theodore Fujita for classifying tornadoes according to the damage they cause and their rotational wind speed. (see also enhanced Fujita scale.) [1]
6181	Ground Nadir	See nadir. [14]
6182	Gyro Compass	See compass: gyroscopic. [14]
6183	Hydrocarbons	Chemical compounds composed of only hydrogen and carbon. They are included under the general term volatile organic compounds (VOCs). [1]
6184	Interrogator	A radar transmitter which sends out a pulse that triggers a transponder. An interrogator is usually combined in a single unit with a responsor, which receives the reply from a transponder and produ-ces an output suitable for feeding to a display system, the combined unit being called an interrogator-responsor. Short for interrogator-responsor. Also called challenger. [14]
6185	Laminar Flow	Low in which the fluid moves smoothly along streamlines which are arranged in parallel layers or sheets; opposite of turbulent flow. Also called streamline flow. [14]
6186	Last Quarter	See phases of the moon. [14]
6187	Marine Chart	See chart: nautical. [14]
6188	Mooring Buoy	See buoy. [14]
6189	Optical Axis	See axis of lens. [14]
6190	Pacific High	A semipermanent high in the subtropical high-pressure belt centered near 30° latitude. The bermuda high is located over the atlantic ocean off the east coast of north america. The pacific high is located off the west coast of north america. Also see subtropical high. [1]
6191	Perturbation	Disturbance in the orbital path of a celestial body, natural or artificial, due to attraction of another body. See lunar inequality. [14]
6192	Psychrometer	Instrument used to measure the humidity of the atmosphere. It comprises two identical thermo-meters, the bulb of one of which is dry, while that of the other is wet and covered by a film of pure water or ice. [14]
6193	Radar Target	An object which reflects a sufficient amount of a radar signal to produce an echo signal on the radar screen. [14]
6194	Random Error	see error: accidental. [14]
6195	Relief Model	A scaled representation in three dimensions of a section of the crust of the earth, or of another heavenly body. A relief model primarily designed to display features on the surface of the earth is sometimes known as a topographic model. [14]
6196	Semidiameter	Half the angle at the observer subtended by the visible disk of a celestial body. Sextant altitudes of the sun and moon should be corrected for semidiameter unless the center is observed, as with a bubble sextant. [14]
6197	Spoil Ground	a sea area where dredged material is deposited. See also dumping ground. [14]
6198	Subpolar Low	A belt of low pressure located between 50° and 70° latitude. In the northern hemisphere, this belt consists of the Aleutian low in the North Pacific and the Icelandic low in the North Atlantic. In the southern hemisphere, it exists around the periphery of the Antarctic continent. [1]
6199	Surface Wave	See wave. [14]
6200	Tide Station	See station. [14]
6201	Tide: Double	A double-headed tide. Also called agger. See high water: double and low water: double. [14]
6202	Transparency	In oceanography, the property of water to transmit light of different wavelengths. Transparency sometimes is measured in percent of radiation that penetrates a distance of one metre. Sometimes it is expressed as the average depth at which a secchi disc disappears and reappears. In photography, a photographic print on a clear base, especially adaptable for viewing by transmitted light. Also, the light-transmitting capability of a material. [14]
6203	Tropic Range	Short for great tropic range. [14]
6204	Year: Civil	A year of the gregorian calendar of 365 days in common years, or 366 days in leap (or bissextile) years. [14]
6205	Aclinic Line	See equator: magnetic. [14]
6206	Aleutian Low	The subpolar low-pressure area that is centered near the Aleutian Islands on charts that show mean sea- level pressure. [1]
6207	Alphanumeric	Contraction of alphabetic-numeric. Characters including letters of the alphabet and numbers. [14]
6208	Angle Of Cut	See angle: crossing. [14]
6209	Angular Rate	See speed: angular. [14]
6210	Antimeridian	The meridian which is 180 deg of longitude from a given meridian. One meridian with its anti-meridian constitutes a complete great circle. [14]
6211	Barrier Reef	A coral reef fronting the shore, at some distance from it, and separated from it by a lagoon or a navigable channel of moderate depth. See also fringing reef. [14]
6212	Bourdon Tube	Closed, curved, flexible tube of elliptic cross-section, which is deformed, according to type, by variations of atmospheric pressure or temperature and so provides a measurement of the particular element. [14]
6213	Cartographer	Person employed in drawing and constructing charts or maps. [14]
6214	Cirrocumulus	A high cloud that appears as a white patch of clouds without shadows. It consists of very small elements in the form of grains or ripples. [1]
6215	Cirrostratus	High, thin, sheetlike clouds, composed of ice crystals. They frequently cover the entire sky and often produce a halo. [1]
6216	Cloud Genera	Ain characteristic mutually exclusive forms of clouds, constituting the basis of the cloud classification included in the international cloud atlas, 1956. The cloud genera are ten in number: cirrus, cirrocumulus, cirrostratus, altocumulus, altostratus, nimbostratus, stratocumulus, stratus, cumulus, cumulonimbus. [14]
6217	Compass Bowl	That part of a compass in which the compass card is mounted. A magnetic compass bowl is usually filled with liquid. The compass bowl turns with the craft while the compass card remains essentially in a north-south direction. [14]
6218	Condensation	The process by which water vapor becomes a liquid. [1]
6219	Conductivity	The ability to transmit, as electricity, heat, sound etc. [14]
6220	Current Line	See current pole. [14]
6221	Current Pole	A pole used to determine the direction and speed of a surface current. The direction is determined by the direction of motion of the pole, and the speed by the amount of an attached graduated line (called current line or log line) paid out in a specified time. [14]
6222	Danger Angle	The maximum (or minimum) angle between two points, as observed from a craft, indicating the limit of safe approach to an offlaying danger. [14]
6223	Echo Ranging	The determination of distance by measuring the time interval between transmission of a radiant energy signal, usually sound, and the return of its echo. [14]
6224	Ekman Bottle	A reversing water bottle which can be closed watertight by means of plates seated in rubber. When at the desired depth, the reversing mechanism is tripped by a messenger. [14]
6225	Enclosed Sea	A gulf, basin, or sea surrounded by two or more states and connected to another sea or the ocean. [14]
6226	Falling Tide	See tide. [14]
6227	False Bottom	See phantom bottom. [14]
6228	False Origin	See coordinates: false. [14]
6229	False Target	See echo: false. [14]
6230	Faye Anomaly	See free-air anomaly. [14]
6231	Fishing Area	See fishing ground. [14]
6232	Flinders Bar	A bar of soft unmagnetized iron placed vertically near a magnetic compass to counteract deviation caused by magnetic induction in vertical soft iron of the craft. [14]
6233	Floating Ice	Any form of ice found floating in water. [14]
6234	Ground Layer	Thin layer of air adjacent to the earth's surface and of a depth which has been variously given as 10 m to 100 m. Also called surface boundary layer. [14]
6235	Ground Range	See ground distance. [14]
6236	Heat Equator	See equator: thermal. [14]
6237	Historic Bay	Historic bays are those over which the coastal state has publicly claimed and exercised jurisdiction and this jurisdiction has been accepted by other states. Historic bays need not match the definition of "bay" contained in the united nations convention on the law of the sea. [14]
6238	Horizon Line	See horizon trace. [14]
6239	Ice Piedmont	Ice covering a coastal strip of low-lying land backed by mountains. The surface of an ice piedmont slopes gently seawards and may be anything from 50 m to 50 km wide, fringing long stretches of coastline with ice cliffs. Ice piedmonts frequently merge into ice shelves. [14]
6240	Igneous Rock	Rock formed by solidification of molten material or magma. [14]
6241	Inclinometer	An instrument for measuring the inclination to the horizontal of the longitudinal axis of an aircraft. See dip circle, wire angle indicator. [14]
6242	Inogen Light	Leading mark based on the interference effect of 3 separately placed raster boards. An arrow pointing in the direction of the line is displayed when not sailing along the leading line. [14]
6243	Interference	Extraneous signals, noises, etc., that hinder proper reception of the desired signal in electronic equipment. See wave interference. [14]
6244	Landing Area	In aeronautical terminology, the part of the movement area intended for the landing or take-off run of aircraft. [14]
6245	Lateral Buoy	See lateral mark [14]
6246	Lateral Mark	In the iala maritime buoyage system a navigation mark used to indicate the port or starboard side of the route to be followed. They are generally used for well-defined channels and are used in conjunction with a conventional direction of buoyage. See also lateral system. [14]
6247	Lee-Side Low	Storm systems (extratropical cyclones) that form on the downwind (lee) side of a mountain chain. In the united states lee-side lows frequently form on the eastern side of the rockies and sierra nevada mountains. [1]
6248	Light Sector	A sector in which a navigational light is visible. See arc of visibility. [14]
6249	Light Vessel	See lightship. [14]
6250	Lower Branch	That half of a meridian or celestial meridian from pole to pole which passes through the antipode or nadir of a place. [14]
6251	Luminescence	Any emission of light at temperatures below that required for incandescence. See bioluminescence, fluorescence, phosphorescence. [14]
6252	Map Parallel	See axis of homology. [14]
6253	Normal Water	A standard sea water preparation, the chlorinity of which lies between 19.30 and 19.50 per mille (0/00) and has been determined to within ± 0.001 per mille. Normal water is used as a convenient comparison standard for chlorinity measurements of sea water samples by titration. It is prepared by the hydrographical laboratories, copenhagen, denmark. Also called standard sea water. [14]
6254	Object-Glass	See objective lens. [14]
6255	Oscillograph	A device for recording or indicating oscillations or changes in an electric current. [14]
6256	Paranthelion	Photometeor of the halo family, consisting of white, round, luminous spots, having a diameter slightly greater than that of the sun, which appears at 120° from it in the case of ordinary paranthe-lia, and at 90° in the case of extraordinary paranthelia. The height of the spots above the horizon is that of the sun. [14]
6257	Partial Tide	See tide. [14]
6258	Pilot Waters	Areas in which the services of a marine pilot are available. Waters in which navigation is by piloting. More usually called pilotage waters in British terminology. [14]
6259	Polar Aurora	See aurora. [14]
6260	Polar Circle	Either the arctic circle (north polar circle) or the antarctic circle (south polar circle). [14]
6261	Polarization	A condition of radiant energy in which the vibrations take place in a regular manner, as in a straight line, circle or ellipse, in a plane perpendicular to the path of travel. [14]
6262	Primary Tide	See tide. [14]
6263	Quartz Clock	See clock: crystal. [14]
6264	Radar Beacon	A transponder beacon transmitting a coded signal on radar frequency, permitting an interrogating craft to determine the bearing and range of the transponder. Also called racon. See ramark. [14]
6265	Radiant Flux	See flux. [14]
6266	Range Finder	An optical instrument for measuring the distance to an object. [14]
6267	Rate Station	See drift station. [14]
6268	Registration	Correct positioning of one component of a composite map image in relation to the other compo-nents. Achieved, for example, by punching sets of holes, having a fixed horizontal relationship to each other, in each component sheet and then attaching the components together using specially designed fasteners. See also punch register system. [14]
6269	Sidereal Day	See day. [14]
6270	Solar System	The sun and other celestial bodies within its gravitational influence, including planets, planetoids, satellites, comets, and meteors. [14]
6271	Sounding Rod	See sounding pole. [14]
6272	Special Mark	In the IALA maritime buoyage system, a special mark indicates an area or feature referred to in nautical documents; it is not primarily intended to assist navigation. [14]
6273	Stadia Lines	Two or more horizontal wires fixed in the diaphragm at equal distances from the axis of telescopes, of theodolites and levels. Also called stadia wires. [14]
6274	Stratosphere	Region of the atmosphere, situated between the tropopause and the stratopause, in which the temperature generally increases with height. From an imperfect analogy with the atmosphere, the term is sometimes applied in oceanography to the nearly uniform masses of cold, deep and bottom water of middle and low latitudes. This layer is separated from the troposphere by the thermocline. [14]
6275	Subtense Bar	A horizontally held bar of precisely determined length, used to measure distances by observing the angle it subtends at the distance to be measured. [14]
6276	Tabular Berg	A flat-topped iceberg. Most tabular bergs form by breaking from an ice shelf and show horizontal banding. [14]
6277	Tide Reducer	The correction that must be applied to a recorded sounding for the height of tide above or below the datum of reference at the time of sounding. [14]
6278	Transit Axis	See axis: horizontal. [14]
6279	Traverse Net	See triangulation net. [14]
6280	True Azimuth	See azimuth. [14]
6281	Type Of Tide	The characteristic feature of the tide (tidal current) determined from the combination of its diurnal and semidiurnal components. Tides are classified as semidiurnal, mixed and diurnal, but there are no sharply defined limits separating the groups. [14]
6282	Water Colour	See sea water: colour of. [14]
6283	Wet Density	The ratio of the weight of the solid particles of a bottom sediment and the contained moisture to its total volume. [14]
6284	Almanac: Air	A periodical publication containing various computed astronomical data primarily intended for use in air navigation. See also ephemeris. [14]
6285	Anastigmatic	(Adj.). Free from astigmatism. Corrected for astigmatism. [14]
6286	Anchor Berth	A designated area of water where a vessel, seaplane, etc. May anchor. [14]
6287	Angle: Check	See check angle. [14]
6288	Angle: Drift	See drift angle. [14]
6289	Angle: Phase	See phase angle. [14]
6290	Angle: Slope	See slope angle. [14]
6291	Apparent Sun	See sun. [14]
6292	Argillaceous	(Adj.). Applied to all rocks or sediments composed partly or completely of clay. [14]
6293	Astenosphere	See mantle. [14]
6294	Astronautics	The science of locomotion and travel outside the earth's atmosphere, involving the problems of artificial satellites and of interplanetary journeys. [14]
6295	Autopositive	A material which gives a positive copy from a positive transparency (or a negative from a negative) by direct processing. [14]
6296	Axis Of Tilt	In photogrammetry, a line through the perspective center perpendicular to the principal plane. [14]
6297	Azimuth Mark	A mark set at a significant distance from a triangulation or traverse station to mark the end of a line for which the azimuth has been determined, and to serve as a starting or reference azimuth for later use. [14]
6298	Back Azimuth	See azimuth. [14]
6299	Backing Wind	Counter-clockwise change of wind direction, in either hemisphere. [14]
6300	Basic Survey	A hydrographic survey so complete and thorough that it does not need to be supplemented by other surveys, and is adequate to supersede, for charting purposes, all prior hydrographic surveys of the area. [14]
6301	Basin: Tidal	A basin affected by tidal forces in which water can be kept at a desired level by means of a gate. [14]
6302	Beach Comber	See comber. [14]
6303	Beam Compass	An instrument consisting of a beam or rod with sliding sockets that hold pencil, pen, or steel points, used together with a scale for plotting exact lengths or for drawing large circles. [14]
6304	Binocular(S)	An optical instrument consisting of a pair of telescopes joined so as to be adaptable to the use of both eyes simultaneously. [14]
6305	Boat Compass	See compass. [14]
6306	Border Break	A cartographic technique to extend cartographic detail of a map or chart beyond the neatline into the margin to show important features. This technique eliminates the necessity of producing an additional chart. Also called blister. [14]
6307	Border Scale	See scale. [14]
6308	Boulder Clay	See till. [14]
6309	Bridge: Draw	A general name for bridges of which part or the entire span of the bridge may be raised or drawn aside to allow ships to pass through. [14]
6310	Bridge: Lift	A movable bridge which is capable of being lifted vertically to allow vessels to pass beneath. [14]
6311	Broadside On	Beam on, as to the wind or sea. [14]
6312	Broken Water	An area of small waves and eddies occurring in what otherwise is a calm sea. [14]
6313	Buoy: Survey	A buoy used by survey ships to control hydrographic surveys. See also buoy-control method. [14]
6314	Cable Length	See cable. [14]
6315	Caution Area	An area to which a cautionary note applies where the mariner needs to be aware of special circumstances influencing the safety of navigation. [14]
6316	Centrosphere	The central core of the earth, composed of dense material, and making up most of its mass. Also called barysphere or core. [14]
6317	Cesium Clock	See clock: cesium. [14]
6318	Channel: Sea	A long, narrow, u-shaped or v-shaped shallow depression of the sea floor usually occurring on a gently sloping plain or fan. A continuously sloping, elongated depression commonly found in cones or abyssal plains and customarily bordered by levees on one or both sides. [14]
6319	Chart Symbol	A character, letter, or similar graphic representation used on a chart to indicate some object, characteristic, etc. May be called map symbol when applied to any map. [14]
6320	Chart: Blank	A chart with a reduced amount of detail serving as cartographic basis for graphical documents of all kinds and for the depiction of reference data. [14]
6321	Chart: Datum	A chart depicting the undulations of the geoid. [14]
6322	Chart: Field	A nautical chart prepared at the survey site, usually contains limited, and/or unedited information. [14]
6323	Chart: Index	An outline chart showing the limits and identifying designation of navigational charts, volumes of sailing directions, or list of lights. [14]
6324	Chart: Pilot	A chart containing information required for safe navigation, including ocean currents, ice at sea, wind roses, storm tracks, isotherms, magnetic variation, great circle routes, limits of trade winds, etc. [14]
6325	Chart: Polar	A chart of the polar areas, or one on a polar projection. [14]
6326	Chart: Radar	A chart designed primarily for use with radar, or one suitable for this purpose. [14]
6327	Chinook Wind	A warm, dry wind on the eastern side of the rocky mountains. In the alps, the wind is called a foehn. [1]
6328	Chromosphere	The reddish layer of incandescent gases around the sun, visible at a total eclipse. A similar layer surrounding a star. [14]
6329	Circular Fix	See fix. [14]
6330	Closing Line	A line that divides the internal waters and territorial seas of a coastal state or the archipelagic waters of an archipelagic state. [14]
6331	Coding Delay	An arbitrary time delay in the transmission of pulse signals. In the loran system this is inserted between the transmission of master and slave signals to prevent zero or small readings, and aid in distinguishing between master and slave station signals. [14]
6332	Coelenterate	One of a phylum of two-staged (sessile and free-floating) organisms. The sessile stage basically is cylindrical and is called a polyp; the free-swimming stage is disc or bell shaped and is called a medusa or jellyfish. [14]
6333	Colour Plate	A general term for a press plate from which any given colour is printed. [14]
6334	Colour Proof	The final proof for checking before printing utilizing all of the negatives involved to produce a copy of the final product with all of the required colors. See also proof. [14]
6335	Compass: Box	See declinatoire. [14]
6336	Compass: Sky	A type of astro compass which utilizes the polarization of sunlight in the sky, designed for use in the arctic during long periods of twilight. It operates whenever the zenith is clear whether or not the sun is visible, but when the sun is more than about 6.5° below or 10° above the horizon, readings are uncertain. [14]
6337	Compass: Sun	A form of astro compass utilizing the shadow of a gnomon. [14]
6338	Compass: Wet	See compass: liquid. [14]
6339	Conical Buoy	A buoy the above water part of which is in the shape of a cone. [14]
6340	Control Mark	A specific object on the ground whose position and/or elevation has been determined or is to be determined. [14]
6341	Copper Plate	Polished plate on which manuscript drawings were formerly engraved for the printing of charts. [14]
6342	Core Catcher	A mechanical device located at the bottom of a core barrel to retain a bottom sample. [14]
6343	Course: Grid	See course. [14]
6344	Course: True	See course. [14]
6345	Current: Ebb	See ebb stream. [14]
6346	Current: Rip	The return flow of water piled up on shore by incoming waves and wind. [14]
6347	Curve: Depth	See depth curve. [14]
6348	Cyclogenesis	The development or strengthening of middle-latitude (extratropical) cyclones. [1]
6349	Datum: Tidal	A level of the sea defined by some phase of the tide, from which water depths and heights of tide are reckoned. [14]
6350	Deceleration	Negative acceleration. [14]
6351	Declinatoire	A combined magnetic compass and straight edge, suitable for use on a plane table to mark the magnetic meridian. Also known as a box compass or trough compass. See also compass: tubular. [14]
6352	Declinometer	A magnetic instrument similar to a surveyor's compass, but arranged so that the line of sight can be rotated to conform with the needle or to any desired setting on the horizontal circle. Used in determining the magnetic declination. See variation. [14]
6353	Densitometer	An electric instrument designed to accurately measure optical density or tone values and used in place of the human eye for such purposes. [14]
6354	Distributary	A river branch which flows away from the main stream without returning to it, as in a delta. [14]
6355	Dredged Area	An area of the bottom of a body of water which has been deepened by dredging. [14]
6356	Drift Bottle	An identifiable sealed bottle which is released into the sea for use in studying currents. [14]
6357	Drum Plotter	A plotter which uses a rotating drum or cylinder to move the drawing base in the direction of one coordinate axis while the plotting head only moves along the other coordinate axis. [14]
6358	Dumb Compass	See pelorus. [14]
6359	Ebb Strength	Phase of the ebb tidal current at the time of maximum velocity. Also, the velocity at this time. Also called strength of ebb. [14]
6360	Electric Log	See log. [14]
6361	Epipolar Ray	The line on the plane of a photograph joining the epipole and the image of an object. Also expressed as the trace of an epipolar plane on a photograph. [14]
6362	Error: Gross	The result of carelessness or a mistake; may be detected through repetition of the measurement. Also called blunder. [14]
6363	Error: Index	The instrumental error which is constant and attributable to displacement of a vernier or some analogous effect. [14]
6364	Error: Swirl	The additional error in the reading of a magnetic compass during a turn, due to friction in the compass liquid. [14]
6365	Evaporimeter	Instrument for measuring the amount of water evaporated into the atmosphere during a given time interval. Also called atmometer, atmidometer. [14]
6366	Fair Tracing	(British terminology). A paper tracing of moderate size for transferring the work from the field boards to the fair charts. [14]
6367	Fairway Buoy	A buoy marking a fairway, with safe water on both sides. [14]
6368	Fall Streaks	Falling ice crystals that evaporate before reaching the ground. [1]
6369	Fata Morgana	The name originally given to a multiple mirage phenomenon often observed over the straits of messina, and supposed to be the work of the faity (in italian: fata) morgana; later, it was applied to any impressive multiple mirage. [14]
6370	Fathom Curve	See fathom line, depth curve. [14]
6371	Feature Code	An alphanumeric code (label) attached to all point, line or area data describing a cartographic feature of particular quality. [14]
6372	Fishing Reef	See fish haven. [14]
6373	Fix: Running	A position determined by crossing lines of position obtained at different times and advanced or retired to a common time, the expression being applied to a position determined by advancing and retiring a line over a considerable period of time. [14]
6374	Flight Strip	A succession of overlapping aerial photographs taken along a single course. [14]
6375	Frontal Wave	A wavelike deformation along a front in the lower levels of the atmosphere. Those that develop into storms are termed unstable waves, while those that do not are called stable waves. [1]
6376	Function Key	A special key on a computer which performs a preprogrammed function. [14]
6377	Funnel Cloud	A funnel-shaped cloud of condensed water, usually extending from the base of a cumuliform cloud. The rapidly rotating air of the funnel is not in contact with the ground; hence, it is not a tornado. [1]
6378	Gale Warning	See warning. [14]
6379	Galvanometer	An instrument for detecting and determining the intensity and direction of an electric current. [14]
6380	Gauge: Depth	A general term for an instrument made to indicate depth of water, especially one in which sea depths are indicated by pressure of water against a spring, or by degree of compression of air in a tube. [14]
6381	Gauge: Float	A tide gauge that is operated by a float in a long, vertical stationary box to which the tide is admitted through an opening in the bottom. Also called box gauge. [14]
6382	Graving Dock	See dock: dry. [14]
6383	Grid Azimuth	See azimuth. [14]
6384	Grid Bearing	See bearing. [14]
6385	Ground Plane	In photogrammetry, the horizontal plane passing through the ground nadir of a camera station. [14]
6386	Ground Swell	A long high ocean swell; also, this swell as it rises to prominent height in shallow water, however, usually not so high or dangerous as blind rollers. [14]
6387	Ground Truth	The information acquired by a field study to calibrate or verify geographical data acquired by remote sensing. [14]
6388	Gyro Sextant	See sextant. [14]
6389	Harbour Line	The line beyond which wharves and other structures cannot be extended. [14]
6390	Headwater(S)	The streams from the sources and upper parts of a river. [14]
6391	Hill Shading	A method of indicating relief on maps by shading normally the slopes facing south and east, i.e. It is assumed that the area mapped is illuminated from the north-west. The method is often used in association with contours. [14]
6392	Hydrographer	A person who studies and practices the science of hydrography; the term is often applied to the person in charge of a hydrographic department or office of a country. [14]
6393	Image: Erect	An image that appears upright or in the same relative position as the object. [14]
6394	Index Mirror	The mirror attached to the index arm of a marine sextant. Also called index glass. [14]
6395	Island Shelf	See continental shelf. [14]
6396	Island Slope	See continental slope. [14]
6397	Kelvin Scale	A temperature scale with zero degrees equal to the theoretical temperature at which all molecular motion ceases. Also called the absolute scale. The units are sometimes called ?degrees kelvin?; however, the correct si terminology is ?kelvins,? Abbreviated k. [1]
6398	Kilogram(Me)	The unit of mass in the si system. [14]
6399	Lamp: Signal	A compact, portable battery-operated electric lamp used as a target for observations or surveys of high precision. The parabolical reflector is mounted in a special case so as to facilitate pointing and adjusting. [14]
6400	Lappened Ice	See anchor ice. [14]
6401	Leader Cable	See cable. [14]
6402	Leeward Tide	See tide. [14]
6403	Leeway Angle	The angle between true heading and track of a vessel caused by wind action. [14]
6404	Level: Dumpy	See levelling instrument: dumpy level. [14]
6405	Level: Plate	A spirit level attached to the plate of a surveying instrument for the purpose of levelling the graduated circle or, indirectly, making the vertical axis truly vertical. [14]
6406	Light Pencil	A bundle of light rays originating at, or directed to, a single point. [14]
6407	Light: Fixed	A signal light that shows continuously, in any given direction, with constant luminous intensity and colour. [14]
6408	Light: Front	See light(s): range. [14]
6409	Light: Point	A luminous signal appearing without perceptible length, as contrasted with a linear light. [14]
6410	Line Of Flow	The vector line showing the direction of current at a given time. Also called streamline. [14]
6411	Line Spacing	Distance between sounding lines. Spacing usually depends on the type of survey, the instruments used, and the demanded accuracy. [14]
6412	Linear Light	See light. [14]
6413	Linear Scale	See scale: bar. [14]
6414	Linear Speed	See speed. [14]
6415	Lock Gate(S)	Pair of massive hinged doors at each end of a lock. [14]
6416	Loop Antenna	A directional antenna consisting essentially of one or more complete turns of wire. [14]
6417	Macroclimate	The general climate of a large area, such as a country. [1]
6418	Magnetograph	A magnetic observatory instrument consisting of one or more (usually 3) variometers, one for each magnetic element recorded, and a recorder. [14]
6419	Major Planet	See planet. [14]
6420	Map: Contour	A topographic map which portrays relief by means of contours. [14]
6421	Marine Borer	Any marine invertebrate that excavates tunnels, holes, or depressions in one or more of a variety of materials by abrasive, chewing, or chemical action. [14]
6422	Marine Light	See light. [14]
6423	Meroplankton	Chiefly the floating development stages (eggs and larvae) of the benthos and nekton. [14]
6424	Microclimate	The climate structure of the air space near the surface of the earth. [1]
6425	Minor Planet	An asteroid. [14]
6426	Mixing Depth	The vertical extent of the mixing layer. [1]
6427	Mixing Layer	The unstable atmospheric layer that extends from the surface up to the base of an inversion. Within this layer, the air is well stirred. [1]
6428	Month: Lunar	See month: synodical. [14]
6429	Nadir Radial	See radial. [14]
6430	Natural Year	See year: tropical. [14]
6431	Navigability	Of a vessel: capability of being controlled and steered. Of a water area: capability of being navigated. [14]
6432	Neap Tide(S)	See tide. [14]
6433	Nimbostratus	A dark, gray cloud characterized by more or less continuously falling precipitation. It is rarely accompanied by lightning, thunder, or hail. [1]
6434	On Soundings	Said of a vessel navigating within the 100-fathom line. In earlier times, said of a vessel in water sufficiently shallow for sounding by hand lead. [14]
6435	Onshore Wind	Wind blowing from sea toward the land. See sea breeze. [14]
6436	Optical Flat	A surface, usually of glass, ground and polished plane within a fraction of a wavelength of light. An optical element or glass blank with an optical flat is used to test the flatness of other surfaces. [14]
6437	Optical Path	The path followed by a ray of light through an optical system. [14]
6438	Oscilloscope	A type of oscillograph that visually records an electrical wave on a fluorescent screen, as of a cathode-ray tube. [14]
6439	Ozalid Print	See print: ozalid. [14]
6440	Panchromatic	(Adj.). Sensitive to light of all colors, as a film or plate emulsion. [14]
6441	Parallax Bar	See stereometer. [14]
6442	Parallax: X-	See parallax: absolute stereoscopic. [14]
6443	Partial Node	The point, line, or surface, in a standing wave system where some characteristic of the wave field has a minimum amplitude differing from zero. [14]
6444	Photoalidade	A photogrammetric instrument having a telescopic alidade, a plateholder, and a hinged ruling arm mounted on a tripod frame. It is used for plotting lines of direction and measuring vertical angles to selected features appearing on oblique and terrestrial photographs. [14]
6445	Photocompose	(v.t.). To combine distinct parts of chart original by photographic processes. [14]
6446	Photogravure	A photoengraving process by which photographs or textual matters are reproduced on intaglio printing plate or rolls from which they may be transferred to paper. [14]
6447	Pigmentation	A colouring of tissue by deposition of pigments. [14]
6448	Pileus Cloud	A smooth cloud in the form of a cap. Occurs above, or is attached to, the top of a cumuliform cloud. Also called a cap cloud. [1]
6449	Pressure Ice	A general term for floating ice which has been squeezed together and in places forced upwards, when it can also be described as rafted ice, hummocked ice, pressure ridge, tented ice. [14]
6450	Print: Ratio	A print in which the scale has been changed from that of the negative or transparency by projection printing. [14]
6451	Pulse Length	The time interval during which the amplitude of a pulse is at or greater than a specified value, usually stated in terms of a fraction or percentage of the maximum value. [14]
6452	Reflectivity	The ratio of the radiant energy reflected by a surface to that incident upon it. [14]
6453	Reproducible	An original drawing, photographic positive or negative on stable base material to be used in the process of reproduction. [14]
6454	Reticle Ring	The ring across which the system of wires, hairs, threads, or the like of a reticle are stretched; or the ring which supports the glass diaphragm when the reticle is a system of lines etched on glass. [14]
6455	Rise Of Tide	The height of high water above datum. Also called tidal rise. [14]
6456	Scale Factor	A multiplier for reducing a distance obtained from a map by computation or scaling to the actual distance on the datum of the map. A conventional modification which may be applied to the majority of map projections. This is the multiplication of the principal scale by some numerical con-stant which is slightly less than unity. This has the effect of changing all particular scales by a corre-sponding amount and, since both maximum and minimum particular scales are similarly modified, the special properties of the projection are unaffected. The effect is to produce a better balance of positive and negative scale errors over the mapped area. [14]
6457	Scale: Large	A scale involving a relatively small reduction in size. A large scale chart is one covering a small area. The opposite is small scale. See scale: natural. [14]
6458	Scale: Small	A scale involving a relatively large reduction in size. A small scale chart is one covering a large area. The opposite is large scale. See scale: natural. [14]
6459	Scale: Speed	A graphic scale by means of which the rate of speed of a survey ship, or the distance travelled in a given time can be determined quickly and accurately. [14]
6460	Sextant: Air	A sextant designed primarily for air navigation. Air sextants are generally provided with some form of artificial horizon. [14]
6461	Signal: Tide	A signal or message conveying information on tidal conditions in the area in question. [14]
6462	Signal: Time	An accurate signal marking a specified time or time interval. It is used primarily for determining errors of timepieces. Such signals are usually sent from an observatory by radio or telegraph, but visual signals are used at some ports. [14]
6463	Snapper: Mud	A small clamshell snapper which is attached to the bottom of sounding lead by means of a hole drilled in the lead. [14]
6464	Snow Pellets	White, opaque, approximately round ice particles between 2 and 5 mm in diameter that form in a cloud either from the sticking together of ice crystals or from the process of accretion. Also called graupel. [1]
6465	Sonar Target	An object which reflects a sufficient amount of a sonar signal to produce a detectable echo signal at the sonar equipment. [14]
6466	Spectroscope	An optical instrument for forming spectra. It is very useful in studying the characteristics of celestial bodies. [14]
6467	Stadia Wires	See stadia lines. [14]
6468	State Of Sky	State of the atmosphere in respect of the amount, genus, height, etc. Of the clouds which are present. [14]
6469	Station Buoy	A buoy used to mark the approximate position of an important buoy or lightship should it be carried away or temporarily removed. Also called marker buoy, watch buoy. [14]
6470	Statute Mile	A unit of distance equal to 1,760 yards or 5,280 feet (1,609.35 m). This mile is generally used on land, and is sometimes called land mile. [14]
6471	Surface Duct	A zone immediately below the sea surface where sound rays are refracted toward the surface and then reflected. They are refracted because the sound velocity at some depth near the surface is greater than at the surface. The rays alternately are refracted and reflected along the duct to considerable distances from the sound source. [14]
6472	Survey: Land	See survey: cadastral. [14]
6473	Taffrail Log	See log. [14]
6474	Tartan Plots	Lattices resulting from the enlargement of small parts of two range and hyperbolic lattices, used for work which has to be carried out on a scale larger than that being used for the main survey. [14]
6475	Thematic Map	See map. [14]
6476	Thermosphere	The atmospheric layer above the mesosphere (above about 85 km) where the temperature increases rapidly with height. [1]
6477	Tide: Rising	The portion of the tide cycle between low water and the following high water. Also called flood tide. The opposite is falling tide. [14]
6478	Tide: Syzygy	The tide which takes place on the afternoon of the day the sun and moon are in syzygy. (this term is now little used). [14]
6479	Tide: Tropic	The tide that occurs twice monthly when the effect of the moon's maximum declination north or south of the equator is greatest. [14]
6480	Time: Summer	See time: daylight saving. [14]
6481	Tinted Areas	Those areas on the nautical chart that are symbolized by a flat colour to indicate the nature of the area. [14]
6482	Topmark Buoy	A buoy with a top mark, or characteristic shape secured at the top to aid in its identification. [14]
6483	True Bearing	See bearing. [14]
6484	Trumpet Buoy	See buoy: sound. [14]
6485	Turning Buoy	A buoy marking a turn, as in a channel. [14]
6486	Undercurrent	A current below the surface, particularly one flowing in a direction or at a speed differing from the surface current. [14]
6487	Uniform Flow	Any current in which neither convergence nor divergence is present. [14]
6488	Veering Wind	Clock-wise change of wind direction, in either hemisphere. [14]
6489	Venturi Tube	The trade name for a short tube of smaller diameter in the middle than at the ends. When a fluid flows through such a tube, the pressure decreases as the diameter becomes smaller, the amount of the decrease being proportional to the speed of flow and the amount of restriction. [14]
6490	Volcanic Ash	Uncemented pyroclastic material consisting of fragments mostly under 4 millimeters in diameter. Coarse ash is 1/4 to 4 millimeters in grain size; fine ash is below 1/4 millimeter. A constituent of some marine sediments. [14]
6491	Warping Buoy	A buoy so located that lines to it can be used for the movement of ships. [14]
6492	Water Signal	See signal. [14]
6493	Wave Cyclone	An extratropical cyclone that forms and moves along a front. The circulation of winds about the cyclone tends to produce a wavelike deformation on the front. [1]
6494	Wave: Direct	A subdivision of the space wave component of the electromagnetic ground wave. This wave is propagated directly through space, i.e., it follows the shortest path between transmitter and receiver. [14]
6495	Wave: Forced	A wave generated and maintained by a continuous force, in contrast to a free wave that continues to exist after the generating force has ceased to act. [14]
6496	Wave: Ground	That portion of a radio wave in proximity to and affected by the ground, being somewhat refracted by the lower atmosphere, diffracted by the surface of the earth and retarded by the resistivity of the earth. Such a wave travels more or less parallel to the surface of the earth. See wave: sky. [14]
6497	Weather Buoy	An ocean data acquisition system (ODAS) used for collecting oceanographic or meteorological information. ODAS’s buoys are up to 40 feet in diameter. [14]
6498	Weather Side	The side of a vessel toward which, or the side of a channel from which the wind is blowing. [14]
6499	Weather Vane	See vane. [14]
6500	Wind Turbine	A tower and associated equipment that generates electrical power from wind. They can be sited offshore and may be either fixed or floating. [14]

Notes:

(v.t) : Verb Transitive
(v.i.) : Verb Intransitive

References:

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