DEPTH FACTOR 



degree of polarization — If a polarized radiance 

 meter witli retardation plate removed is 

 directed to accept the beam, the polarizer 

 rotated 180 degrees and maximum and mini- 

 mum radiances recorded, then tlie degree of 

 polarization is the ratio of tlie diflerence between 

 maximum and minimum radiances to the sum 

 of them, that is, tlie ratio of the polarized frac- 

 tion to the total energy. (8) 



delta — An alluvial deposit, roughly triangular or 

 digitate in shape, fonned at the mouth of a 

 stream or tidal inlet. See bay delta, bird-foot 

 delta, tidal delta. 



delta moraine — Glacial deposit in deep water 

 with which delta deposits are associated. (2) 



demersal — 1. Fishes which live on or near the 

 bottom. 



2. The eggs of certain bony fishes, which have 

 a hard and smooth or adhensive membrane and 

 sink to the bottom. (43) 



densitometer — A device for measuring the den- 

 sity of sea water or of bottom sediments. 



density — 1. The ratio of the mass of any sub- 

 stance to the volume occupied by it ; the recipro- 

 cal of specific volume. 



2. In oceanograjjliy, 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 (39.2°F). It is 

 thus dimensionless and expressed in units of 

 sigma-t. 



density current — The flow (caused by density 

 differences or gravity) of one current through, 

 under, or over another; it retains its unmixed 



DELTA 



(AmUi LOMCK, 1939.) 



identity because of density differences from the 

 surrounding water. See turbidity current. 



density layer — A layer of water in whicli density 

 increases with depth enough to increase the 

 buoyancy of a submarine. (Submariner's term 

 for pycnocline.) 



deperming — Tlie process of clianging the mag- 

 netic condition of a ship by wrapping a large 

 conductor around it a numljer of times in a 

 vertical plane, athwartsliips, and energizing tlie 

 coil thus fonned. If a single coil is placed 

 horizontally around the ship and energized, the 

 process is called flashing if the coil remains 

 stationary, and wiping if it is moved up and 

 down. See degaussing. (68) 



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. The 

 process is deposition. 



deposition — See deposit. 



depression — 1. This term is no longer recom- 

 mended by ACUF for any low place, hollow, or 

 basin of any size on the sea bed which is sur- 

 rounded by higher elevations. See basin, 

 trench, trough, seachannel. 



2. In meteorology, an area of low pressure; a 

 low or a trough. This is usually applied to a 

 certain stage m the development of a tropical 

 cyclone, to migratory lows and troughs, and to 

 upper-level lows and troughs that are only 

 weakly developed. (5) 



depth — 1. The vertical clistance from a specified 

 sea level to the sea floor. The charted depth is 

 the recorded distance from the tidal datum to the 

 bottom surface at the point, using an assumed 

 velocity of sound in waters of 800 fathoms per 

 second (U.S.) and with no velocity or slope 

 corrections made. 



2. Formerly used in combination with a ship 

 name to designate a record deep sounding, for 

 example, Milwaukee Depth; no longer recom- 

 mended by the ACUF. 



depth anomaly (AZ) graph — A graph con- 

 structed to detennine the difference between the 

 computed or thermometric depth and the ideal 

 or assumed depth of reversal of thermometers 

 attached to a Nansen bottle. 



depth contour — See isobath. 



depth curve — See isobath. 



depth excess — The difference between the bottom 

 depth and the depth at which the sound veloc- 

 ity is equal to either (1) the surface velocity, 

 when there is no layer depth, or (2) the maxi- 

 mum velocity in the surface layer. 



depth factor — The factor by which the apparent 

 depth of the water measured stereoscopically is 

 multiplied to give the true depth. This factor is 

 a ratio of the tangent of the incidence angle to 

 the tangent of the refraction angle. See shoal- 

 ing coefficient. (73) 



47 



