SPINDEL: PHASE FLUCTUATIONS, COHERENCE AND INTERNAL WAVES 



yet to be established. At the turning point I also observed a sharp 

 rise, but I can't tell how much because it was above a cycle. And 

 at that point we are stuck, whereas your data are fine enough that 

 you can follow the phase through several cycles and find out what is 

 happening. 



Dr. R. P. Porter (Woods Hold Oceanographic Institute) : I want 

 to reinforce your comment. We attribute the depth dependence we see 

 in our phase fluctuations precisely to that turning point argument, 

 coupled with the fact that the layer of nearly constant sound 

 velocity occurs right near the region where the internal wave 

 activity appears to be the greatest. 



We feel it is a qualitative conclusion that we really can't test 

 accurately because of the breakdown of the ray theory in that region. 

 But we have come to that same conclusion. 



Dr. Flatte: Why do you think the ray theory has broken down? 

 Why not just integrate the true path through that region? You know 

 the length. 



Dr. Porter: Because it is a caustic. I do not think it is 

 valid — 



Dr. H. A. DeFerrari (Rosenstiel School of Marine and Atmospheric 

 Science, University of Miami) : We do not know where the ray turns. 

 There is an ambiguity. As the grazing angle becomes small, any 

 slight perturbation to the sound-speed profile causes a turn. So 

 if you want to integrate through there, you may not be on the same 

 ray that strikes your receiver. 



Dr. Porter: Put it another way. In that ray you have diffrac- 

 tion effects. 



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