FITZGERALD: CONVERGENCE ZONE DEPENDENCE ON FREQUENCY 



Dr. Raisbeck: There are possible excitations in which all the 

 energy would fall in the range where the convergence zones had the same 

 length for the two frequencies . 



Dr. Fitzgerald: That's right. Yes. 



Dr. John S. Hanna (Office of Naval Research): I'd like to make 

 a comment. I think if I could adopt a ray-tracing point of view for 

 just a moment, at the low frequency the two different periods that you 

 observed in the convergence zone correspond respectively to the RR 

 propagating rays and the RSR propagating rays. The only reason for 

 making that observation is that I would invite some of you to take a 

 look at the PARKA data, particularly for the 500-foot source and 

 50 Hz center frequency. You can see quite clearly those two different 

 periods and the way they change the function of range in -exactly the 

 same way you showed. 



Dr. Fitzgerald: As I indicated, the region in which the inter- 

 ference wavelength was different was the region in which the phase 

 velocity of the mode was less than the speed of sound at the surface, 

 which indicates it's an RR. 



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