126 



DEEP-WATER TRANSMISSION 



RADIO SOUW 

 SIGNAL SIGNAL 



— 450 

 YDS 



73.5 db 

 ATTENUATION 



RADIO 

 TRACE 



■■ -4 , 



SOUND 

 TRACE 



• 



• 



--• ► — 



-i-1 1 1 L% 



5000 10,000 



Figure 44. Records of received signals at various ranges under downward refraction. 



anomalies of the long pulses. The transmission anom- 

 aly for 100-msec pulses in the shadow zone is usually 

 between 40 and 60db. Figure 45 shows that about4to 

 8 db must be subtracted from these values to find the 

 transmission anomaly of the 10-sec pulse, which may 

 be regarded as essentially a continuous tone in these 

 observations. On the other hand, 7 db must be added 

 to find the anomaly in terms of average intensity 

 instead of average peak amplitude. Since these two 

 corrections about cancel out, 40 to 60 db is the trans- 

 mission anomaly for the intensity of long pulses in 

 the shadow zone. 



A theoretical value for this transmission anomaly 

 may be computed on a somewhat simplified picture. 

 Although the scattered sound is itself refracted by 

 the prevailing vertical velocity gradient, most of the 

 scattered rays are inclined so steeply that they may 

 be regarded as straight lines. With this assumption, 



too 200 SOD 1000 2000 



RANGE IN YARDS 



Figure 45. Increase of average peak amplitudes for 

 long pulses. 



The sound received in the shadow zone, at least out 

 until about 2,500 or 3,000 yd, is probably sound 

 scattered from the main beam at considerable depth 

 up to the hydrophone near the surface. The scatter- 

 ing coefficient required to explain the observations 

 can be readily estimated from the transmission 



