HANNA: DESIGN OF TRANSMISSION LOSS EXPERIMENTS 



DISCUSSION 



Dr. J. S. Hanna (Office of Naval Research) : What I have here 

 (in Figure 16) is a schematic representation of a path which refracts 

 through the bottom and one which is reflected from the interface. What 

 I intended to have these paths correspond to is essentially what is back 

 at the source and again at the receiver. 



The point that I wanted to make here is that even if both of 

 those paths are present in the data, the only thing that they can do 

 to you is produce structure in the bottom reflectivity that you would 

 infer, but they cannot give you reflectivities which are greater 

 than one. 



The reason why, I believe, is that if these two paths have ampli- 

 tude A and they reach this boundary, the reflected path will have 

 some amplitude less than A which I have indicated by aA here. That 

 means that the energy, which is remaining to travel along this path, 

 is essentially 1 - a times the original amplitude, and the most that 

 can happen when these two recombine is that you get A back, but not 

 more than that and, in general, perhaps less than that. 



So that I don't believe in principle that the combination of 

 those two paths is the problem. 



Mr. M. A. Pedersen (Naval Undersea Center): No, that's not 

 quite true, because you have a slope discontinuity there, you are 

 bound to have a caustic down in that bottom medium. There is a slope 



540 



