DRAFT 6 megs UNDERWATER SOUND PROPAGATION At five locations on the NORI2Z0N's cruise, temperature and salinity were measured to depths of as great as 2500 meicis to more than 400: meters. For these stations computations we: made of the speed of underwater sound. At all locations the sound speed profiles from top to bottom were very similar except in the depth range of the tnermoclinee Thus, sound [n tes speeé data are shown plotted only for one station es an exampl: iBe 9 de hj ( At all locations the speed of underwater sound is nearly constant above the thermocline. In general, cenditions are now relatively good for nearesurface propagation of underwaici sound in the PPG. As summer progresses and the trace wind weakens the surface will be warmed. * Then sound speed will be greater near the surface than elsewhere below it and more sour? energy will refract downward and be lost from the layer above the thermocline. Thus, scund propagation conditions in upper weters will become less fevorable. Commencing at tne top of the thermocline, sound speed decreases rapidly with decreasing tempereture (Fig. 9). It et reaches 2 minimum, generally at 1000 to 1200 meters, excep at one location where it was least, at 800 meters. mum is the axils of the deep SCFAR channel. This wini- For comparison, off the west coast of the United States this minimum is found at 600 to 800 meters Gepthe Below the minimum the sound speed increases with depth. oa wh ws The increase is very slow down to below 2000 meters. a Thus ary +4 s