BROWNING: ENVIRONMENTAL FACTORS AFFECTING LOW FREQUENCY 

 PROPAGATION IN THE OCEAN 



Figure 8 shows the results of DiNapoli's program for two different 

 types of bottom: (A) a hard, low-loss bottom which essentially has no 

 loss at all except at the very high grazing angles, and (B) a high-loss 

 bottom, where there are large losses per bounce. 



To put this in terms that experimentalists really get a feeling 

 for and understand, we would run the program at a particular frequency 

 for the two bottom conditions and various profiles, and compare the 

 results obtained for a high-loss bottom with those obtained for a low- 

 loss bottom. 



The idea was that if we were at a high enough frequency so that 

 there was no significant leakage out of the sound channel, then the 

 results obtained by the two methods would be the same. In other 

 words, if the sound energy does not see the bottom, it does not matter 

 what the bottom is made of. Figure 8 is a demonstration of this point. 

 These results correspond to a high frequency, several kilo-Hertz, and 

 it is seen that basically the same answer obtains for either type of 

 bottom, because all the energy is going right down the sound channel. 



Figure 9 illustrates a case, at 50 Hz, where the bottom loss is 

 obviously a factor. The minute the sound starts hitting the bottom, 

 the high-loss bottom is just going to suck it right up, and the prop- 

 agation loss gets much greater with the high-loss bottom than with 

 the low-loss bottom. 



We found, amazingly enough, that for frequencies above 300 Hz 

 there was no significant difference using the high-loss or the low- 

 loss bottom in DiNapoli's program. 



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