DISCONTINUOUS DISTRIBUTION. See BIPOLARITY. 



DISPHOTIC ZONE. See EUPHOTIC ZONE. 



DISSIPATION LOSS . The dissipation loss of a trans- 

 ducer connecting an energy source and an energy 

 load is the transmission loss measured by the ratio 

 of the input power of the transducer to its output 

 power. (4) 



spreading of orthogonals in the direction of wave 

 travel. This denotes an area of decreasing wave 

 height and energy concentration. 



2. In wind set-up phenomena, the 

 decrease in set-up observed under that which would 

 occur in an equivalent rectangular basin of uniform 

 depth, caused by changes in plan-form or depth. 

 Also the increase in basin width or depth causing 

 such decrease. (11) 



DISSOLVED OXYGEN . Dissolved oxygen is measured on 

 almost every oceanographic expedition because of its 

 biological importance and for our understanding of 

 the chemical processes in the sea, including the 

 circulation of the ocean, and composition of bottom 

 materials. Oxygen can be added to the sea only in 

 the upper layers, by absorption of air, and in a 

 layer strictly limited by the depth of light pene- 

 tration, by photosynthesis. At the surface, oxygen 

 can bejlost from the sea by exchanges with the at- 

 mosphere, but at all depths it is consumed by the 

 respiration of plants and animals, and during the 

 decomposition of organic materials by bacteria. 

 Reactions of oxygen with reduced materials such as 

 sulphides, iron, manganese, other auto-oxidizable 

 substances, and the consumption of oxygen actuated 

 by enzymes, are of limited extent and largely con- 

 fined to the surface and bottom layers. The oldest 

 and most widely used technique for measuring oxygen 

 is the Winkler method. (35) 



DISTORTION . Distortion is an undesired change in 

 waveform. Noise and certain desired changes in 

 waveform, such as those resulting from modulation 

 or detection, are not usually classed as distortion. 

 (2) 



DIURNAL. 1. Daily, recurring once each day. 

 (e.g., lunar day or solar day). (11) 



2. Having a period or cycle of approxi- 

 mately one tidal day. Thus, the tide is said to 

 be diurnal when only one high water and one low 

 water occur during a tidal day, and the current is 

 said to be diurnal when there is a single flood and 

 a single ebb period in the tidal day. A rotary 

 current is diurnal if it changes its direction 

 through all points of the compass once each tidal 

 day. A diurnal constituent is one which has a 

 single period in the constituent day. The symbol 

 for such a constituent is usually distinguished by 

 the subscript 1. (14) 



DIURNAL INEQUALITY . The difference in height of 

 the two high waters or of the two low waters of 

 each day; also the difference in velocity between 

 the two flood currents or the two ebb currents of 

 each day. The difference changes with the decli- 

 nation of the moon and to a lesser extent with the 

 declination of the sun. In general the inequality 

 tends to increase with an increasing declination, 

 either north or south, and to diminish as the moon 

 approaches the equator. Mean diurnal high water 

 inequality (DHQ) is one-half the average difference 

 between the two high waters of each day over a 19- 

 year period. It is obtained by subtracting the 

 mean of all high waters from the mean of the higher 

 high waters. Mean diurnal low water inequality 

 (DLQ) is one-half the average difference between 

 the two low waters of each day over a 19-year 

 period. It is obtained by subtracting the mean of 

 the lower low waters from the mean of all low 

 waters. Tropic high water inequality (HWQ) is the 

 average difference between the two high waters of 

 the day at the times of the TROPIC TIDES. Tropic 

 low water inequality (LWQ) is the average differ- 

 ence between the two low waters of the day at the 

 times of the tropic tides. Mean and tropic in- 

 equalities as defined above are applicable only 

 when the type of tide is either semidiurnal or 

 mixed. Diurnal inequality is sometimes called 

 declinational inequality. (4) 



DIVERGENCE LOSS . Divergence loss is that part of 

 the transmission loss which is due to the spread- 

 ing of sound rays in accordance with the geometry 

 of the situation. For example, in case of spher- 

 ical waves emitted by a point source, the sound 

 pressure at a point 20 yards distant from the 

 source will be only one-half as great as the sound 

 pressure 10 yards from the source. (9) 



DIVING PHYSIOLOGY . Since Physiology covers the 

 study of the functions and activities of the 

 various organs and parts of living bodies. Diving 

 Physiology may be described as the study of the 

 physical and chemical functions of human beings 

 while in the water environment . 



DL. 



U. S. Navy ship designation for a Frigate. 



DLG . U. S. Navy ship designation for a Guided 

 Missile Frigate. 



DM . U. S. Navy ship designation for a Minelayer, 

 Destroyer. 



DM RAYDIST . A range-elli 

 used in navigational posi 



Four radio transmitt 

 required to operate the s 

 measuring frequencies and 

 cies to transmit phase re 

 each ground station back 



DM Raydist is simila 

 and the DECCA HI-FIX syst 

 circular plotting systems 



ptical measuring system 



tioning. 



ers and frequencies are 



ystem, the two distance 



two additional frequen- 

 lationship information at 

 to the ship. 



r to the two range DECCA 

 ems in that they are all 

 (29) 



DMS . U. S. Navy ship designation for a Minesweeper, 

 Destroyer. 



DOCK (SLIP) . 1. The space between two piers. A 

 PIER is sometimes erroneously called a dock. 



2. A basin or enclosure for recep- 

 tion of vessels, and provided with means for con- 

 trolling the water level. A wet dock is one in 

 which water can be maintained at any level by clos- 

 ing a gate when the water is at the desired level. 

 A dry dock is a dock providing support for a vessel, 

 and means for removing the water so that the bottom 

 of the vessel can be exposed. A dry dock consist- 

 ing of an artificial basin is called a graving 

 dock; one consisting of a floating structure is 

 called a floating dock. (17) 



DOD . Department of Defense. (U.S.) 



DOLDRUMS (EQUATORIAL CALMS) . A nautical term for 

 the EQUATORIAL TROUGH, with special reference to 

 the light and variable nature of the winds. (24) 



DOLPHIN . A post or group of posts, used for moor- 

 ing or warping a vessel. The dolphin may be in the 

 water, on a wharf, or on the beach. (17) 



DOME . A transducer enclosure, usually stream- 

 lined, used with echo-ranging or listening devices 

 to minimize turbulence and cavitation noises aris- 

 ing from the passage of the transducer through the 

 water. (6) 



DOME INSERTION LOSS . 

 LOSS) . 



(See SONAR DOME INSERTION 



DIVERGENCE. 



In refraction phenomena, the 



DOME LOSS PATTERN . (See SONAR DOME LOSS PATTERN) , 



35 



