HANNA: DESIGN OF TRANSMISSION LOSS EXPERIMENTS 



after I think I have done as well as I possibly can toward modeling 

 the part of the propagation that is alledged to take place in the 

 water itself. 



Mr. R. L. Martin (Naval Underwater Systems Center, New London 

 Laboratory): In the Labrador Basin, Stan Delia has made some measure- 

 ments of an area of little interest to the Navy for bottom loss be- 

 cause there is so much depth excess, but he has been very careful to 

 separate out a direct path and a bottom reflected path. He has been 

 able to do this successfully down to angles of almost 5 degrees 

 grazing, and starting at 10 degrees he has observed what we call 

 "negative" bottom loss. 



Even when you are very careful about your experimental procedure, 

 using shots that are detonated deep in the water column, the receiver 

 deep in the water column, and other factors, you still make that 

 observation of negative bottom loss. 



The way models are used today, you can't throw that into a model 

 because every time the ray intersects the bottom, the negative loss is 

 put into that ray. But it does indicate that in those areas where we 

 make that type of observation, that you perhaps have to include the 

 bottom into your model, because it is going to be a function of the 

 point in the water column where you make the measurement. 



Dr. H. Weinberg (Naval Underwater Systems Center New London 

 Laboratory): Why don't we just simplify the problem and forget that 

 you even have a bottom. Just consider the ray that goes into a 

 little bottom region with a strong but positive gradient. By changing 

 that gradient, you can get just about any type of answer you want. 

 Clearly, by making that gradient strong enough, you can focus the 

 energy enough to get an increase in the power of its intensity. 



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