BEAM TRAWL 



beam trawl — A type of trawl which has a rigid 

 front (or beam) fastened between two metal 

 shoes the soles of which slide over the bottom. 

 As the trawl passes over the bottom, fish and 

 other marine life are captured within the at- 

 tached net. 



beam width — The beam width of a directional 

 transducer of a given frequency in a given 

 plane which includes tlae beam axis is the angle 

 included between the two directions, one to the 

 left and the other to the right of the axis, at 

 which the angular deviation loss has a specified 

 value. 



beam wind — A nautical term for a crosswind, es- 

 pecially a wind blowing 90 degrees from a ship's 

 heading. 



bearing — The horizontal direction of one terres- 

 trial point from another. It is usually meas- 

 ured from 000 degrees at the reference direction 

 clockwise through 360 degrees. (66) 



beat — The periodic variation that results from the 

 superposition of two simple harmonic oscilla- 

 tions whose frequencies differ by a small amount. 

 It involves a periodic increase and decrease of 

 amplitude at the beat frequency which is equal 

 to the difference in the frequencies of the two 

 parent signals. Thus, if two pure tones having 

 frequencies of 300 and 400 cycles per second are 

 heard by a listener, he will also sense a frequency 

 equal to the difference, 100 cycles per second. 

 This is the beat frequency. 



beating — A wave phenomenon which occurs when 

 two or more waves of different frequencies be- 

 come superimposed. The resultant wave has 

 amplitude maximum ("beats") at the frequency 

 equal to the difference of the frequencies of the 

 initial waves. xS'ee surf beat. (5) 



Beaufort force — (or Beaufort number) . A num- 

 ber denoting the speed (or "strength") of the 

 wind accordmg to the Beaufort wind scale. 



(5) 



Beaufort number — See Beaufort force. 



Beaufort scale — See Beaufort wind scale. 



Beaufort wind scale — A system of estimating 

 and reporting wind speeds, devised in the early 

 nineteenth century (1806) by Admiral Beaufort 

 of the British Navy. It was originally based on 

 the effects of various wind speeds on the amount 

 of canvas that a full-rigged frigate of the period 

 could carry, but has since been modified and 

 modernized. In its present form for interna- 

 tional meteorological use it equates (a) Beau- 

 fort force (or Beaufort number), (b) wind 

 speed, (c) descriptive term, and (d) visible ef- 

 fects upon land objects or sea surface. (5) 



bed — 1. The smallest division of a layered rock 

 series se^iarated from material above or below by 

 a more or less well defined change in character. 

 2. The ground upon which a body of water 

 rests. The term is usually used with a modifier 

 to indicate tlie type of water body, as sea bed. 

 See bottom. (68) 



bedded — See bed. 



bedding cleavage — A cleavage or break that is 

 parallel to the bedding. (68) /See bed. 



bedding joint — A joint that is parallel to the bed- 

 ding. (68) /See bed. 



bedding plane — Division planes which separate 

 t he individual layers. ( 68 ) See bed. 



bed load — See load. 



bedrock — Any solid rock underlying soil or un- 

 consolidated sediments. 



bel — A unit of level when the base of the loga- 

 ritlim is 10. Use of the bel is restricted to levels 

 of quantities proportional to power. See 

 decibel. (69) 



bell — See umbrella. 



bellicatter — Variant spelling of bally cadder, 

 meaning an ice foot. 

 (59) 



belt — (also called ice helt, sea bar). A long area 

 of sea ice bounded by open water or land. De- 

 pending on their length, belts can vary from a 

 few kilometers to more than 100 kilometers (54 

 n. miles) in width. (74) 



bench — 1. A level or gently sloping erosion plane 

 inclined seaward. 



2. A nearly horizontal area at about the level 

 of maximum high water on the sea side of a 

 dike. 

 (61) 



bench mark — A permanently fixed point of known 

 elevation. A primary bench mark is one close 

 to a tide station to which the tide staff and tidal 

 datum originally are referenced. 



bending — Upward or downward motion in a sheet 

 of ice, caused by lateral pressure. This is the 

 first stage in the formation of pressure ice, and 

 is characteristic of thin and very plastic ice. 

 See rafting, tenting. ( 68 ) 



bends — See decompression sickness. 



Benguela Current — A strong current flowing 

 northward along the southwest coast of Africa ; 

 it is formed by the West Wind Drift and the 

 Agulhas Current. The Benguela Current 

 flows toward the Equator, gradually leaves the 

 coast, and becomes the South Equatorial Cur- 

 rent. 



benthic — (also called benthonic). 1. That por- 

 tion of the marine environment inhabited by ma- 

 rine organisms which live permanently in or on 

 the bottom. {See figure for classification of 

 marine environments.) 



2. Pertaining to all submarine bottom terrain 

 regardless of water depth. 



benthic division — A primary division of the sea 

 which includes all of the ocean floor. {See fig- 

 ure for classification of marine environ- 

 ments.) 



benthonic — See benthic, benthos. 



benthos — 1. Bottom dwelling forms of marine life. 

 Many authorities include certain fishes, such as 

 stingrays and flounders, which spend much of 



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