HANNA: DESIGN OF TRANSMISSION LOSS EXPERIMENTS 



So, the model makers are going to have to adjust. We can't 

 change the ocean. 



Dr. Weinstein: John (Dr. Hanna) , concerning another point, you 

 started out by saying, let's assume the source levels are properly 

 taken care of, but in fact they are not, because the measurement of 

 the source level is made at a relatively short range when you are 

 doing this kind of work. 



At these ranges you are still in the shock wave region and not in 

 the pseudo-acoustic region. You find that the pressure- time curve 

 changes with range in such a fashion that there is a transfer of 

 energy from the high frequencies to the lows. 



This, in itself, would give you an apparent negative bottom loss 

 if you apply spherical spreading as your means of correction, or if 

 you calculate the propagation loss assuming that you have a caustic 

 source. 



Dr. Hanna: It is true that the analysis performed on this data 

 is more complicated than only worrying about the estimated loss that 

 you are going to compare to the measured transmission loss. 



There is the whole problem of source level. I am not sure that 

 I would agree at this point that it is a mechanism for getting nega- 

 tive reflectivities except if the source level is too high or too 

 low, whichever way it has to be to make that happen. 



I would like to make just one more comment about the particular 

 sound velocity structure that I used here and what rays are and are 

 not present at certain ranges in the problem for that particular 

 geometry. 



550 



