BROWNING: ENVIRONMENTAL FACTORS AFFECTING LOW FREQUENCY 

 PROPAGATION IN THE OCEAN 



Figure 4 shows the type of attenuation data Bob Mellen presented. 

 It varies from location to location, but tends to be a relatively con- 

 sistent picture of what is happening. Also, Figure 4 contains the 

 Thorp formula. 



After doing experiments in the deep ocean, we went to Hudson Bay, 

 which was a shallow location, and found that the attenuation co- 

 efficients (Figure 5) were even higher than the Thorp formula, which 

 is based on what we had consistently measured in the deep ocean. 



Our first thought was: Is this experiment being contaminated by 

 bottom effects? This, of coixrse, not only entered our minds but the 

 modelers were also quick to point this out. At this time, Fred 

 DiNapoli in our laboratory was polishing his FFP program, so we said, 

 "Let's get together and exchange ideas and see what we can come up 

 with." It could be done with any of the many modern techniques such 

 as Chick Weinberg's or others that have been mentioned, but it 

 happened to be at a time that it would provide a good test for the 

 FFP and also a good test for attenuation measxirements . 



What we were trying to answer in rough terms was this (see 

 Figure 6) : Was there an effect besides the basic absorption caused 

 by diffraction out of the sound channel or scattering as flellen has 

 talked about? In other words, we wanted to see which of these com- 

 ponents contributed to the increase in attenuation above the Thorp 

 formula. 



Figure 7 shows roughly what the conditions were up North. The 

 Hudson Bay profile has a relatively shallow axis with a very strong 

 gradient on the top. The average bottom depth was roughly about 

 500 feet. The bottom tends to be hard: bedrock over a thin layer 

 of sandy clay. 



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