HANNA: DESIGN OF TRANSMISSION LOSS EXPERIMENTS 



and there wasn't — at least the way I would read it — any indication 

 of contributions from these paths that might have reflected, let's 

 say, in that deep interface at all. 



Dr. C. W. Norton, Sr . (Applied Research Laboratory of the 

 University of Texas at Austin) : I think the point is that whether 

 there are two or more rays, your point is still proven. You are 

 wanting to show that you cannot get positive bottom-loss values, 

 and the total reflection, if there is no loss at the bottom, is 

 unity. So where there are two or three rays that add together, 

 you still would only get a total amplitude of unity if they are in 

 base. That is all you set out to establish. 



Dr. Hanna: Yes, that's exactly right. It sounds like I have 

 convinced at least one person. 



The point I wanted to make is, even if one improved this picture 

 to include for low grazing angles the possibility that some of the 

 incident energy is reflected and not refracted through this layer, 

 that you take that incident energy and send part of it along one path 

 and the remainder along the other path, and that some place in the 

 problem they may come together again. But the most that you can do 

 is get back to the original intensity of that path, less the spread- 

 ing loss. 



Dr. J. B. Mersey (Office of Naval Research) : John, have you 

 experimented with nonlinear gradients in the sediment? If there is 

 a second derivative to the gradient, I believe that caustic is 

 guaranteed, right? I can assure you this kind of intensification is 

 seen experimentally and it is very striking indeed. Its explanation 

 is illusive. 



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