DOME-SHAPED ICEBERG . An ICEBERG eroded in such a 

 manner that Its upper surface is well-rounded and 

 smoothly contoured. This type iceberg is more com- 

 mon in the antarctic than the arctic. (25) 



DOO . Director, Office of Oceanography. The pro- 

 posed office to be established within the Natural 

 Sciences Department of UNESCO. 



DOPPLER CONSTANT . When the change in frequency is 

 expressed in cycles per second, the source frequen- 

 cy in kilocycles per second, and the range rate in 

 knots, the factor of proportionality is known as 

 the Doppler constant for echo transmission. (4) 



DOPPLER CURRENT METER . The Doppler Current Meter 

 is an acoustic current meter based on the Doppler 

 shift principle. With this device a collimated 

 beam of ultrasonic energy is projected into the 

 water and a volume reverberation signal received. 

 The meter detects the difference between the trans- 

 mitted and received frequencies, this difference 

 being proportional to the speed of the water past 

 the meter. The device can be made to indicate 

 sense as well as flow rate. The current meter con- 

 sists of an oscillator driving the transmitting 

 crystal, an amplifier tuned to the oscillator fre- 

 quency (10 mc) and driven by the receiving crystal, 

 a detector, and an emitter follower as the output 

 of an audio frequency stage. (30) 



DOPPLER EFFECT . The Doppler effect is the phenom- 

 enon evidenced by the change in the observed fre- 

 quency of a wave in a transmission system caused by 

 a time rate of change in the effective length of 

 the path of travel between the source and the point 

 of observation. (2) 



DOPPLER SHIFT . The Doppler shift is the change in 

 the observed frequency of a wave, due to the Dop- 

 pler effect. (2) 



DORSAL . Toward or pertaining to the back, or upper 

 surface. (19) 



DOUBLE EBB . An ebb current having two maxima of 

 velocity separated by a smaller ebb velocity. (14) 



DOUBLE FLOOD . A flood current having two maxima of 

 velocity separated by a smaller flood velocity. (14) 



DOUBLE TIDE . A double-headed tide, that is, a high 

 water consisting of two maxima of nearly the same 

 height separated by a relatively small depression, 

 or a low water consisting of two minima separated 

 by a relatively small elevation. Sometimes called 

 an agger. (14) 



DOWNCOAST . In United States usage, the coastal 

 direction generally trending towards the south. 

 (11) 



DOWN DOPPLER . (See UP DOPPLER) . 



DOWNDRIFT. The direction of predominant movement 

 of littoral material. (11) 



DRAFT . The depth to which a vessel is submerged. 

 Draft is customarily indicated by numerals called 

 draft marks at the bow and stern. It may also be 

 determined by means of a DRAFT GAUGE. (17) 



DRAFT GAUGE . A hydrostatic instrument installed 

 in the side of a vessel, below the light load line, 

 to indicate the depth to which a vessel is sub- 

 merged. (17) 



DRAG . See SEA ANCHOR 



DRAI . Dead reckoning Analog Indicator. 



DREDGING BUOY . A buoy marking the limit of an area 

 where dredging is being performed. (17) 



DRIFT . 1. The effect of the velocity of fluid 

 flow upon the velocity (relative to a fixed exter- 

 nal point) of an object moving within the fluid; 

 the vector difference between the velocity of the 

 object relative to the fluid and its velocity rela- 

 tive to the fixed reference. 



2, The speed of an ocean current. In 

 publications for the mariner, drifts are usually 

 given in miles per day or in knots. (24) 



DRIFT BOTTLE . A bottle, of one of various designs, 

 the sea for use in studying 

 a card, identifying the date 

 to be returned by the finder 

 e of recovery. The bottle 

 ballasted as to minimize 



which is released into 

 currents . It contains 

 and place of release, 

 with the date and plac 

 should be designed and 

 direct wind effects. 



Since the path of 

 mated between release 

 erally only a few per 

 inefficient, although 

 also DRIFT METHODS.) 



a bottle can only be esti- 

 point and recovery, and gen- 

 cent are returned, this is an 

 inexpensive technique. (See 

 (24) 



DRIFT CARD . A card, such as is used in a DRIFT 

 BOTTLE, encased in a buoyant, waterproof envelope 

 and released in the same manner as a drift bottle. 

 Cheaper and lighter than bottles, drift cards 

 are especially suited to dropping in large quanti- 

 ties from aircraft, and it is supposed that the 

 card, having less freeboard than a bottle, is less 

 affected by wind. (24) 



DRIFT CURRENT . Slow-moving ocean current. Name 

 is especially applied to the continuations of the 

 GULF STREAM as it branches on leaving the American 

 Continent to proceed across the Atlantic Ocean, and 

 also to continuations of the KUROSHIO as it crosses 

 the Pacific Ocean. (14) 



DRIFT ICE . Any ice that has drifted from its place 

 of origin. 



DRIFT ICE FOOT . Same as RAMP. (17) 



DRIFT LEAD . A lead placed on the bottom to indicate 

 movement of a vessel. At anchor the lead line is 

 usually secured to the rail with a little slack and 

 if the ship drags anchor, the line tends forward. 

 A drift lead is also used to indicate when a vessel 

 coming to anchor is dead in the water or when it is 

 moving astern. A drift lead can be used to indi- 

 cate current if a ship is dead in the water. (17) 



DRIFT METHODS . Accuracies obtainable by this 

 method are determined by the navigational accuracy 

 with which positions of the drifting device may be 

 fixed, as well as by the ability of the device to 

 be unaffected by influences other than the current 

 under measurement. The primary advantage of this 

 method is that anchoring of the ship is not re- 

 quired . 



Drifting devices include woodchips, bottles, 

 cards, confetti, dyes, etc., as well as more so- 

 phisticated devices such as drogues, telemetering 

 buoys, and neutral buoyancy floats. Since all of 

 the surface devices are at least partially exposed 

 to the winds and extend to some depth below the 

 water, they may not truly measure surface drift, 

 and data must be viewed with caution. Another 

 technique involving drift is the lowering of cur- 

 rent meters from a drifting ship. Frequent, ac- 

 curate positioning is necessary in this method to 

 correct for the movement of the ship. A difficulty 

 with freely-drifting devices is that instantaneous 

 measurements are not possible, and only time- 

 averaged currents may be obtained . 



Subsurface currents may be measured by the 

 drift method with drogues suspended at any given 

 depth on a wire between a surface buoy and a weight. 

 The complete device is made at negligible cost from 

 a surplus parachute, piano wire, a weight and a 

 float. (35) 



36 



