DECIBAR 



decibar — A unit of pressure used principally in 

 oceanography. One decibar (10^ dynes per 

 square centimeter) equals 0.1 bar. 



In the ocean, hydrostatic pressure in decibars 

 very nearly equals the corresponding depth in 

 meters. (5) 



decibel — (abbreviated db). A value that ex- 

 presses the comparison of sound of two different 

 intensities. This value is defined as 10 times 

 the common logarithm of the ratio of the two 

 sound intensities. 



declination — (also called variation). 1. At any 

 given location, the angle between the geographi- 

 cal meridian and the magnetic meridian; that 

 is, the angle between true north and magnetic 

 north. Declination is either "east" or "west" 

 according as the compass needle points to the 

 east or west of the geogi-aphical meridian. (5) 



2. The angle that the sun, moon, planets, or 

 stars make with the plane of the Equator. 



3. See solar declination, lunar declination, 

 declinational reduction — The processing of high 



and low water tide observations or flood and ebb 

 tidal current observations to obtain quantities 

 which result from the effect of changes in the 

 declination of tlie moon. 



decompression sickness — (also called iends, 

 caisso7i disease, com-pressed-air illness). A con- 

 dition resulting from the formation of gas 

 bubbles in the blood or tissues of divers durmg 

 ascent. Depending on their number, size, and 

 location, these bubbles may cause a wide variety 

 of symptoms including pain, paralysis, un- 

 consciousness, and occasionally death. 



deep — This term is no longer recommended by 

 the ACUF for a relatively small area of excep- 

 tional depth found in a depression type of 

 feature. The term was generally restricted to 

 depths greater than 3,000 fathoms. 



deepening — In meteorology, a decrease in the cen- 

 tral pressure of a pressure system on a constant- 

 height chart, or an analogous decrease in height 

 on a constant-pressure chart; the opposite of 

 filling. The term is usually applied to a low 

 rather than to a high, although technically it is 

 acceptable in either sense. (5) 



deep scattering layer — (also called DSL, false 

 iottom, phantom hottoin) . The stratified popu- 

 lation (s) of organisms in most oceanic watere 

 which scatter sound. The scattered sound is 

 recorded on echo-sounder records as a uniform, 

 horizontal band or stripe, and such layers gen- 

 erally are found during the day at depths from 

 100 to 400 fathoms. A layer rarely is less than 

 25 fathoms thick and may be as much as 100 

 fathoms thick. Several layers often are re- 

 corded at the same time and may be continuous 

 horizontally for many miles. Most layers typ- 

 ically undergo diurnal vertical movements. See 

 shallow scattering layer, surface scattering 

 layer, diurnal vertical migration. 



deep sea anchoring winch — A large size winch 

 used to anchor an oceanographic/hydrographic 

 ship in deep water. Ordinarily this type of 

 winch uses steel wire rope in lengths of about 

 20,000 to 35,000 feet. Some types use specially 

 tapered wire particularly when anchoring in 

 great dejpths, while others use wire of about 

 V2-inch diameter. 



Deep Underwater Nuclear Counter — (abbre- 

 viated DUNG). A submersible gamma ray 

 spectrometer used from ships for in situ detec- 

 tion of ocean gamma radiation. The DUNG 

 system was developed by the U. S. Naval Ord- 

 nance Laboratory for the detection of artificially 

 introduced radioactive constituents in the ocean. 

 It represents the first successful application of 

 gamma spectrometric technique to in situ ocean 

 radioactivity measurements and has since been 

 adapted for oceanographic usage by the U. S. 

 Naval Oceanographic Office. 



deep water — In wave forecasting deep water 

 means that the depth of the water is large com- 

 pared with the wavelength of the longest wave 

 generated by the wind. In general, waves may 

 be considered deepwater waves when the depth 

 of the water layer is greater than one-half wave- 

 length. (46) 



deepwater wave — (also called short toave). A 

 surface wave the length of which is less than 

 twice the depth of the water. The velocity of 

 deepwater waves is independent of the depth 

 of the water. (5) /S'ee shallow water wave. 



deflection of the vertical — The angle at a point 

 on the earth (geoid) between the vertical and 

 the direction of tlie normal to the spheroid of ref- 

 erence tlirough the point. 



degaussing — Neutralization of the strength of the 

 magnetic field of a ship by means of suitably 

 arranged electric coils permanently installed in 

 the ship. (68) See deperming. 



degenerate amphidromic system — A system of 

 cotidal lines whose center or nodal (no-tide) 

 point appears to be located on land rather than 

 in the open ocean. {See figure for cotidal 

 chart.) 



degree — 1. A unit of temperature. 



2. A unit of angular distance; 1/360 part of a 

 circle. 



(5) 

 degree-days of frost — The number of degrees 



that the mean daily air temperature fell below 

 the freezing point of fresh or saline waters. 

 The total number of degree-days of frost dur- 

 ing a specific period is determined by adding 

 the deficiency of the mean air temperature from 

 the freezing point for each clay in the period. 

 Thus, if the mean air temperature on three 

 consecutive days is 20°, 10°, and 0°F, the total 

 number of degree-days of frost, taking the 

 freezing point of sea water at 30°F, would be 

 10 -f 20 -I- 30 = 60. 



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