HANNA: DESIGN OF TRANSMISSION LOSS EXPERIMENTS 



One thing I can say with absolute certainty is that, setting 

 aside for the moment the question of whether you think the constant 

 gradient that I chose in the bottom is at all realistic, if you 

 accept the sound velocity structure, that I outlined above, to trace 

 rays, I can promise that in that particular case for the ranges from 

 14 to 30 miles, roughly, there is only one path which refracts in 

 that strong gradient then comes back at those ranges. 



Now, the thing that I would certainly admit to the possibility 

 of is the following: It may be that for more complicated sound 

 velocity structures and for different values of, say, this initial 

 gradient, and the way that behaves with depth, that you can indeed 

 construct the kind of situations that you mentioned. That is, that 

 at the ranges I considered, you have steeper paths which come back 

 into the problem. 



I would not quarrel with the possibility of doing that. The 

 only thing that I would maintain is that with this particular specific 

 example there is only that one path for those ranges. 



What that may be telling us is that this example is not really 

 representative of most of the cases that you had in your experience. 



Dr. M. Schulkin (Naval Oceanographic Office): You don't have a 

 negative bottom loss going continually out in range. It's just the 

 first one where there is an apparent gain over inverse square 

 spreading, because you have a convergence zone there. Like the other 

 convergent zones that you take for granted in the water column, you 

 have a 3 dB loss the distance level from there on, because you have 

 10 log R spreading as you continue down the path. 



It is no violation of the conservation of energy. If you focus 

 your energy at some points, you lose it at other points in the vertical 

 column, say at that range. 



551 



