Ray versus mode differences in reverberation modeling solutions for environments with high boundary scattering loss.

Abstract

Several of the problems for the first Reverberation Modeling Workshop yielded interesting differences between solutions obtained with ray and normal mode methods. These particular problems were defined with high boundary scattering loss. A bottom reverberation case at 3.5 kHz with a down-refracting sound speed profile (Problem VI) will be considered as a case in point. The ray solutions show a “direct path” contribution unaffected by the bottom scattering loss as long as a direct path can reach the bottom, while the mode solutions obtained to date show a lower reverberation level during this period due to modal attenuation. These differences occur in both incoherent and coherent reverberation solutions for both rays and modes. Arguments will be presented that indicate the correctness of the ray solutions for this case. Suggestions will also be made on how the mode approach can be used to obtain solutions in agreement with the ray method. [Work supported by ONR and the Navy Program Executive Office C4I (PMW 120).]