AUSTRALIA CURRENT . Branch of the SOUTH EQUATORIAL 

 CURRENT of the Pacific Ocean, which leaves the lat- 

 ter in the neighborhood of the Fiji Islands and 

 flows southwesterly until it reaches the east coast 

 of Australia where it takes a southerly direction 

 along this coast. (14) 



AUTEC . Atlantic Underwater Test and Evaluation 

 Center, a Navy test center located in the Tongue 

 of the Ocean section of the Bahamas. 



AUTOTROPHIC . Organisms able to manufacture their 

 own food, such as green plants. (18) 



AUXOSPORE . A reproductive cell in diatoms usually 

 resulting from the union of two smaller cells or 

 their contents and associated with rejuvenescence 

 in cells that have become progressively smaller 

 because of repeated divisions. (20) 



AV. 



U. S. Navy designation for a Seaplane Tender. 



AVAILABLE POWER . The rate at which a given source 

 would deliver energy to a load having an impedance 

 which is the conjugate of the source impedance is 

 designated as the available power of that source. 

 (4) 



AVAILABLE POWER LOSS . The available power loss of 

 a transducer connecting an energy source and an 

 energy load is the transmission loss measured by 

 the ratio of the source power to the output power 

 of the transducer. (4) 



AVE. U. S. Navy designation for an Advanced 

 Aviation Base Ship. 



AVERAGE AREA OF THE HUMAN BODY . The average area 

 of the human body is about 2500 square inches. (37) 



AVERAGE LIMIT OF ICE . Average seaward extent of 

 ice during a normal winter. 



AVM . U. S. Navy designation for a Guided Missile 

 Ship. 



AVP. U. S. Navy designation for a Small Seaplane 

 Tender. 



AVS. U. S. Navy designation for an Aviation Supply 

 Ship. 



AVT . U. S. Navy designation for an Auxiliary Air- 

 craft Transport. 



AW . U. S. Navy designation for a Distilling Ship. 



AXIS OF ACOUSTIC SYMMETRY . For many transducers 

 the three-dimensional directivity is such that it 

 may be represented by the surface generated by 

 rotating a two-dimensional directivity pattern 

 about the axis corresponding to the reference bear- 

 ing of the transducer. This axis may then be 

 described as an axis of acoustic symmetry, or, more 

 briefly, as the acoustic axis. (4) 



AZCHERNIRO . Azov and Black Sea Research Institute 

 of Marine Fisheries and Oceanography (USSR) . 



AZIMUTH . Azimuth of a body is the arc of the 

 horizon intercepted between the north or south 

 point and the foot of the vertical circle passing 

 through the body. It is reckoned in degrees from 

 either the north or south point clockwise entirely 

 around the horizon. Azimuth of a current is the 

 direction toward which it is flowing, and is 

 usually reckoned from the north point. (14) 



AZORES HIGH . See BERMUDA HIGH. 



B 



BACK . 1. Of the wind, to change direction in a 

 counterclockwise direction in the northern hemi- 

 sphere, and a clockwise direction in the southern 

 hemisphere. Change in the opposite direction is 

 called veer. 



2. To go stern first, or to operate the 

 engines in reverse. (17) 



BACKBEACH . See BACKSHORE. 



BACKGROUND NOISE . Background noise is made up 



of sound from a variety of sources, other than the 



desired signal, as indicated by the block diagram 

 below: 



H 



^ 

 ^ 



TRAFFIC NOISE 



BACKRUSH . The seaward return of the water follow- 

 ing the uprush of the waves. For any given tide 

 stage the point of farthest return seaward of the 

 backrush is known as the limit of backrush or limit 

 of backwash. (10) 



BACKS PATTERING . See REVERBERATION. 

 BACKSCATTERING CROSS SECTION. The acoustic back- 



scattering cross section of an object is an area 

 equal to 4Tr times the product of the square of a 

 unit distance and the square of the sound pressure 

 scattered by the object, back in the direction from 

 which the sound has come as observed at unit dis- 

 tance from the acoustic center of the object, 

 divided by the square of the sound pressure of the 

 plane wave incident on the object. The unit of the 

 cross section is the square of the unit distance. 

 (2) 



BACKSHORE (BACKBEACH) ■ That zone of the shore or 

 beach lying between the foreshore and the coast 

 line and acted upon by waves only during severe 

 storms, especially when combined with exceptionally 

 high water. (10) 



BACKWASH . Water or waves thrown back by an obstruc- 

 tion such as a ship, breakwater, cliff, etc. See 

 also BACKRUSH. (10) 



BAGUIO. See TYPHON. 



BAGUIO . A tropical cyclone. The term is customari- 

 ly used only in the Philippine Islands. (17) 



BALI WIND . A strong east wind at the eastern end 

 of Java. (17) 



10 



