BROWNING: ENVIRONMENTAL FACTORS AFFECTING LOW FREQUENCY 

 PROPAGATION IN THE OCEAN 



DISCUSSION 



DR. S. W. MARSHALL (Naval Research Laboratory) : In your dis- 

 cussion of the Hudson Bay data you showed that after you strip out 

 the deep rays the transmission loss goes like 1/R plus an attenu- 

 ation term. Now, if the rays hit the bottom many times over the 

 course of 100 kilometers and even though (as we agree we can't do) 

 you assign so many dB loss per bottom bounce, then that translates 

 to so many dB loss per 100 kilometers, which is a linear function 

 of the range. How can you separate that from what you would attri- 

 bute to the attenuation? 



DR. D. G. BROWNING (Naval Underwater Systems Center New London 

 Laboratory) : I think when you look at the arrival structure it 

 would be obvious to you if the paths weren't going along the axis 

 but were bottom reflected. For example, I believe recently there's 

 been an experiment conducted in Baffin Bay where you see this happen. 

 When you get to very low frequencies the energy is going out of the 

 channel and hitting the bottom and it's a very loss-less bottom 

 there, so it comes back and you will see a whole train of 

 arrivals. 



DR. MARSHALL: Yes, but in the very shallow water of Hudson Bay 

 can you separate those arrivals? 



DR. BROWNING: Yes. That's surprising — Even Lake Superior. 

 We went to Lake Superior which is about the weakest channel you 

 could find, and everybody said, "Oh, you're going to have to record 

 FM because the arrivals are going to be falling over one another, 

 and you're going to have a heck of a mess." 



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