120 



DEEP-WATER TRANSMISSION 



RAY DIAGRAM 



BT INTORMATION 



ui 100 



RECEIVING END 



HYDROPHONE DEPTH A 



T 



HYDROPHONE DEPTH O 



2000 4000 



SOUND FIELD DATA 



EOOO 



4890 4940 4990 



SOUND VELOCITY IN FT PER SECOND 



DATE 

 TIME 



4-16-1944 

 I6S0 



BT CLASS NAN 



WATER DEPTH 680 FM 



SEA I 



SWELL 3 



WIND FORCE 2 



4000 

 RANGE ' IN tAROS 



6000 



Figure 36. Sample transmission anomaly plot. 



most of the runs made off San Diego. While these pat- 

 terns are by no means fundamental, Table 1 suggests 

 that they provide a natural classification for the 

 data. 



It is evident from these tables that when sharp 

 temperature gradients are present at the surface, 

 straight-Une graphs are unlikely. In the following 

 discussion, transmission runs made with sharp tem- 

 perature gradients present in the top 30 ft are there- 

 fore treated separately from those made in the pres- 

 ence of weaker gradients. 



5.4.1 Sharp Temperature Gradients 

 in Top 30 ft 



When the temperature gradient in the top 30 ft is 

 sharp and extends all the way to the surface, theory 

 predicts a sharp downward bending of the sound 

 beam, and a shadow zone of low sound intensity at 

 fairly close ranges. This expectation is generilly ful- 



filled, provided that the difference of temperature be- 

 tween the surface and 30 ft is more than 0.7 F, and 

 the hydrophone is above 100 ft. Samples of such 

 curves are shown for the shallow hydrophones in 

 Figures 36 and 37 as well as in Figure 34. Since the 

 surface temperature for most of the UCDWR trans- 

 mission runs off San Diego was in the neighborhood 

 of 70 F, this critical value is 1/100 of the surface 

 temperature, which is the dividing line between 

 NAN and CHARLIE patterns. 



While the ray theory can explain the qualitative 

 features of the sound field observed with NAN pat- 

 terns, it cannot predict exactly the transmission 

 anomalies to be expected under different conditions. 

 The detailed dependence of sound transmission under 

 these conditions on the temperature structure and on 

 the hydrophone depth is an important subject on 

 which considerable data are available. This informa- 

 tion is summarized in the following pages. First, the 

 correlation between transmission data and the com- 



