a transducer that cannot be actuated at its outputs 

 by waves In such a manner as to supply related waves 

 at Its inputs. (1) 



UNIT AREA ACOUSTIC IMPEDANCE . The quotient obtained 

 by dividing (1) the phasor corresponding, at a given 

 frequency, to the acoustic pressure by (2) the 

 phasor corresponding, at the same frequency, to the 

 volume velocity per unit area. (4) 



UNIVERSAL TIME . See GREENWICH MEAN TIME, 



UNSA. United Nations Specialized Agencies. 



UPCOAST . In United States usage; the coastal 

 direction generally trending towards the north. 

 (11) 



UP DOPPLER . When a target is moving toward a 

 transducer the echo will be of higher frequency 

 than the reverberation regardless of whether the 

 range is opening or closing. When the echo is of 

 higher frequency than the reverberation it is said 

 to have an Up Doppler. Similarly, when the echo 

 is of lower frequency than the reverberation it is 

 said to have a Down Doppler, which indicates a 

 component of target motion away from the trans- 

 ducer. (4) 



UPDRIFT . The direction opposite that of the pre- 

 dominant movement of littoral material. (11) 



UPLIFT . The upward water pressure on the base of 

 a structure or pavement. (11) 



UPRUSH . See RUN-UP. 



UPWELLING . The rising of water toward the surface 

 from subsurface layers of a body of water. Up- 

 welling is most prominent where persistent wind 

 blows parallel to a coastline so that the resul- 

 tant wind-driven current sets away from the coast 

 (see EKMAN SPIRAL). It constitutes a distinct 



cllmatogenetic Influence by bringing colder water 

 to the surface. Over the open ocean, upwelling 

 occurs wherever the wind circulation is cyclonic, 

 but is appreciable only in areas where that circu- 

 lation is relatively permanent. It is also obser- 

 vable when the southern trade winds cross the 

 equator . 



The upwelled water, besides being cooler, is 

 richer in plant nutrients, so that regions of up- 

 welling are generally also areas of rich fisheries. 

 (12) 



URSTROWTHAL ■ A large channel cut by a substantial 

 melt-water stream, flowing along the edge of an 

 ICE-SHEET. (27) 



URV. 



Underseas research vehicle. 



US A ID . United States Aid for International Develop- 

 ment. 



USC&GS . United States Coast & Geodetic Survey. 

 The USC&GS is the nation's oldest (formed in 1807) 

 scientific body and the chief civilian oceano- 

 graphic agency in the U. S. 



USCG . United States Coast Guard. 



(US)GS . Geological Survey (Department of Interior) . 



USN. United States Navy. 



(USN)HO . Hydrographic Office (although now offi- 

 cially designated U.S. Naval Oceanographic Office 

 (NAVOCEANO) H. 0. is still used in referring to 

 charts and publications). 



UST. Undersea Technology. 

 (US)WB . Weather Bureau. 



UTS. Underwater Telephone System. A sonar system 

 -- consisting of a transducer, a receiver-trans- 

 mitter unit and a control box. 



V 



VACUOLE. A cavity within the PROTOPLASM containing 

 a solution of sugars, salts, pigments, etc., to- 

 gether with colloidal materials . (18) 



VACUUM. From a practical viewpoint, a condition 

 where sufficient air has been removed from a con- 

 tainer so that any remaining air will not affect 

 the characteristics of the device beyond an allow- 

 able amount. Theoretically, a perfect vacuum is 

 space from which all the air and gases have been 

 removed; this is never attained in actual practice. 

 (36) 



VALLEY ICEBERG (DRYDOCK ICEBERG) . An ICEBERG 

 eroded in such a manner that a large U-shaped slot 

 extends through the iceberg with large pinnacles 

 or slabs on either side. Sometimes the slot is 

 awash. These icebergs do not turn over, but sail 

 on as majestically as a well-ballasted ship. Val- 

 ley icebergs deteriorate chiefly by CALVING and 

 melting at the water line. When the lightened 

 iceberg rises a series of water lines circling the 

 base is exposed. (25) 



VAN PORN SAMPLER . This sediment sampler consists 

 of a plexiglas cylinder closed at each end by an 

 ordinary rubber force cup. The two cups are con- 



nected by a length of surgical rubber tubing inside 

 the cylinder, pre-stressed enough to permit the 

 force cups to retain the sample in the cylinder. 

 In the armed position the two cups are pulled out- 

 side the cylinder where they are restrained by a 

 releasing mechanism attached to the outside wall. 

 Two short loops of wire connect the cups to the re- 

 leasing mechanism. The cups are released under- 

 water by sending a messenger down the hydrographic 

 wire. This sampler does not invert, which prevents 

 use of reversing thermometers in conjunction with 

 sampling. (30) 



VDS . Variable-Depth Sonar. 



VEGETATIVE EURYHALINE . See STENOHALINE . 



VEGETATIVE STENOHALINE. See STENOHALINE. 



VELOCIMETER . The Velocimeter is an instrument used 

 for the in situ measurement of the speed of sound 

 in the sea and other natural waters. The operation 

 of the velocimeter is based upon the sing-around 

 principle developed by C. E. Tschiegg and M. 

 Greenspan of the National Bureau of Standards. 

 Two electroacoustic transducers and a reflector are 

 mounted to form a sound path of fixed length in 

 water. This sound path along with the necessary 

 amplifiers and blocking oscillator form the essen- 

 tial operating components of a sing-around circuit. 

 In operation, a pulse of acoustic energy is trans- 

 mitted through the water, received, amplified and 

 used to generate another pulse of acoustic energy. 

 The repetition or sing-around frequency of this 



125 



