SUMMARY 



Contrary to popular belief, ray theory is an accurate and efficient means 

 of investigating low frequency acoustic propagation in the ocean. Of course, in 

 this report ray theory has not been used in its classical sense. 



Several illustrative examples proved that it is possible to design a single 

 propagation model that agrees with analytic solutions and measured data, as 

 well as other computer programs. This effort is more difficult than one may 

 realize, for once a computer program is timed to the actual environmental con- 

 ditions of a real ocean, it may be impossible to input data for which analytic 

 solutions are known. The apparently simple task of comparing programs is in 

 reality even more difficult than a comparison with analytic solutions. First, 

 one must have access to the programs being compared. Second, the programs 

 must treat the input data similarly. Finally, the programs must treat the out- 

 put data similarly. For example, how is one to compare coherent phase propa- 

 gation loss predictions with those of a random phase program ? 



Although all the computer models discussed above have been designed within 

 the last few years, the theories upon which they are based are much older. 

 Therefore, it is felt that improved computing facilities rather than improved 

 acoustic theories have been responsible for improved prediction capabilities. 



The future of ray theory may prove quite different. Application to unstrat- 

 ified media, random media, etc. is the next logical step, but these theories need 

 more development before they can be implemented into practical prediction 

 models. 



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