DEPTH FINDER 



depth finder — An instrument for determining the 

 depth of water, particularly an echo sounder. 

 (68) 



depth ice — 1. See anchor ice. 



2. Small particles of ice formed below the 

 surface of the sea when it is churned by wave 

 action. 



depth of breaking — See breaker depth. 



depth of compensation — See compensation 

 depth. 



depth of frictional influence — See depth of f ric- 

 tional resistance. 



depth of frictional resistance — (or depth of fric- 

 tional influence) . The depth at which the wind- 

 induced current direction is 180 degrees from 

 that of the wind. {See figure for Ekman 

 Spiral.) 



derelict — Any property abandoned at sea, often 

 of sufficient size as to constitute a menace to 

 navigation. See jettison. (68) 



desalination of sea water — The process by which 

 enough dissolved salts are removed from sea 

 water to render it potable. The most common 

 method for desalting sea water is distillation, 

 with the favored form being the "multi-flash" 

 process whereby sea water is made to evaporate 

 in low-pressure chambers. See boiling point. 



Other methods employed for desalting include 

 the separation of salts by freezing, the use of 

 special membranes to extract all salts, and elec- 

 trodialysis, a method whereby the ions in sea 

 water are drawn through plastic membranes by 

 electric fields. 



design wave — In the design of harbors, harbor 

 works, etc., the type or types of wave selected 

 as having the characteristics against which pro- 

 tection is desired. ( 73 ) 



detritus — (or debris). Any loose material pro- 

 duced directly from rock disintegration. 



deuterium — (symbol H2 or D). See heavy 

 water. 



devilfish — See octopus, manta ray. 



diadactic structure — See graded bedding. 



diagenesis — The chemical and physical changes 

 that sediments undergo after their deposition, 

 compaction, cementation, recrystallization, and 

 perhaps replacement, which result in lithifica- 

 tion. 



diastrophism — The process or processes by which 

 the crust of the earth is deformed and continents 

 and ocean basins, plateaus and mountains, flex- 

 ures and folds of strata, and faults are produced. 



diatom — One of a class (Bacillariophyceae) of 

 microscopic phytoplankton organisms, posses- 

 sing a wall of overlapping halves (valves) im- 

 pregnated with silica. Diatoms are one of the 

 most abundant groups of organisms in the sea 



and the most important primary food source of 

 _ marine animals. See diatomaceous ooze. 



diatomaceous ooze— A pelagic siliceous sediment 

 composed of more than 30 percent diatom tests, 

 up to 40 percent calcium carbonate, and up to 

 25 percent mineral grains. This sediment gen- 

 erally is restricted to high latitudes or areas of 

 upwelling such as the Gulf of California. See 

 ooze. 



diatom film — See primary film. 



diffracted wave— A wave whose front has been 

 changed in direction by an obstacle or other non- 

 homogeneity in the medium other than by 

 reflection or refraction. (3) 



diffraction — The bending of waves (sound, water, 

 light, etc.) around obstacles. For example, 

 when a portion of a train of waves is interrupted 

 by a barrier such as a breakwater, the effect of 

 diffraction is manifested by propagation of 

 waves into the sheltered region within the 

 barrier's geometric shadow. 



diffuse attenuation function — A mathematical 

 formulation of the relationship between the 

 illuminance {Eo) at the surface, the illumin- 

 ance {Ej.) at a depth (X), and the attenuation 

 coefficient {k). 



E,=Eoe-^^ 



(Strictly this equation relates to monochromatic 

 light only, but it is a sufficient approximation to 

 illuminance data for practical purposes.) 



diffuser — A device used to alter the angular dis- 

 tribution of the radiant flux from a source, 

 depending essentially on the phenomenon of 

 diffusion. (8) 



diffusion — The spreading or scattering of matter 

 under the influence of a concentration gradient 

 with movement from the stronger to the weaker 

 solution. 



diffusion coefficient — The constant of propor- 

 tionality between the rate of diffusion across a 

 plane area and the concentration gradient 

 normal to that plane. 



diffusivity — A measure of the rate of diffusion 

 of a property, appearing as the factor K in the 

 diffusion equation 



dt 



where q is the property diffused, and V ^ is the 

 Laplacian operator. The diffusivity has dimen- 

 sions of a length times a velocity ; it varies with 

 the property diffused, and for any given prop- 

 erty it may be considered a constant or a func- 

 tion of tempei-ature, space, etc., depending on 

 the context. (5) 

 dilatancy — The expansion of granular masses such 

 as sand when deformed because of rearrange- 

 ment of the grains. ( 2 ) 



48 



