150 



SHALLOW-WATER TRANSMISSION 



-5 



10 



< 



s 

 o 



IS 



eo 



25 



30, 



1000 2000 3000 



RANGE IN YARDS 



Figure 7. Transmission over STONY bottoms. 



4000 



mately 30 db. For shorter ranges, there is a significant 

 difference between the anomalies at different hydro- 

 phone depths. With the hydrophone deeper than 

 100 ft, the transmission anomaly is almost linear and 

 increases at the rate of about 10 db per kyd. For the 

 more shallow hydrophone depths, there is a much 

 more precipitate drop at short range. With the hydro- 

 phone at 16 ft, the median transmission anomaly at 

 1,000 yd is 26 db. From 1,000 to 3,000 yd, it drops 

 only another 8 db, resembling in this respect the trans- 

 mission of sound in the shadow zone in deep water. 



Figure 11 shows a typical run over a soft MUD 

 bottom in the presence of a pronounced negative 

 temperature gradient. Just as in deep water, the 

 sound level at shallow depth begins to drop rapidly 

 at a shorter range than does the level at considerable 

 depth. At all hydrophone depths, the transmission 



anomaly increases sharply at the approximate range 

 of the predicted shadow zone boundary. A slight 

 recovery of the sound level recorded by the two 

 shallow hydrophones is noted at almost exactly the 

 range at which the axis of the reflected beam rises to 

 the depth of the hydrophone. This recovery is, how- 

 ever, not very pronounced. While it increases the 

 sound level at 2,400 yd to approximately 10 db above 

 the level which would have been recorded in deep 

 water under similar circumstances, the transmission 

 anomaly still amounts to about 25 db. 



Effect of Wind Force 



UCDWR has carried out an analysis of the effect 

 which the roughness of the surface has on sound 

 transmission in shallow water over well-reflecting 

 bottoms such as ROCK and SAND. 



