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	Eng ID	Term	Definition
	81	AIS	See AUTOMATIC IDENTIFICATION SYSTEM
	82	albedo	The ratio of radiant energy reflected to that received by a surface, usually expressed as a percentage.
	83	alga	A plant of simple structure which grows chiefly in water, such as the various forms of seaweed.
	84	aliasing	An occurence in tidal analysis when the sea level varies with a period that is less than the sampling period. Due to the varying position of... more An occurence 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.
	85	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 s... more 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.
	86	alignment	The placing of objects along a straight line. In NAVIGATION, the bringing into line of two or more conspicuous objects, such as LIGHTS, BEAC... more 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.
	87	alignment correction (tape)	See TAPE: ALIGNMENT CORRECTION.
	88	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.
	89	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... more 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.
	90	almanac	A periodical publication of astronomical data useful to a navigator. It contains less information than an ephemeris, and values are generall... more 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.
	91	almanac: air	A periodical publication containing various computed astronomical DATA primarily intended for use in AIR NAVIGATION. See also EPHEMERIS.
	92	almanac: nautical	An annual publication containing various computed astronomical DATA primarily intended for use in MARINE NAVIGATION. See also EPHEMERIS.
	93	almucantar	Any SMALL CIRCLE on the CELESTIAL SPHERE parallel to the HORIZON. Also called parallel of altitude.
	94	alphanumeric	Contraction of alphabetic-numeric. Characters including letters of the alphabet and numbers.
	95	alt-azimuth instrument	An instrument equipped with both horizontal and vertical graduated CIRCLEs, for the OBSERVATION of horizontal and vertical DIRECTIONS or ang... more An instrument equipped with both horizontal and vertical graduated CIRCLEs, for the OBSERVATION of horizontal and vertical DIRECTIONS or angles.
	96	altimeter	An instrument that indicates directly the HEIGHT above a reference surface.
	97	altimeter: barometric	A sensitive ANEROID BAROMETER calibrated to read the HEIGHT above a pressure datum according to the standard atmospheric pressure-to-height ... more A sensitive ANEROID BAROMETER calibrated to read the HEIGHT above a pressure datum according to the standard atmospheric pressure-to-height relationship.
	98	altimeter: pulse radio	See ALTIMETER: RADIO.
	99	altimeter: radar	See ALTIMETER: RADIO.
	100	altimeter: radio	Any instrument used for determining an aircraft's flight altitude by the measurement of time intervals between the emission and return of el... more 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.
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