Thomas N. Lawrence
Nancy R. Bedford
Appl. Res. Labs., Univ. of Texas at Austin, P.O. Box 8029, Austin, TX 78713
Simple up slope propagation of underwater acoustic energy can usually be modeled by an adiabatic normal-mode approximation, provided the slope is not too severe. Bottom interacting paths in such an environment are usually sufficiently attenuated to make consideration of mode coupling unnecessary. An environment further complicated by an offshore rise can cause additional acoustic energy to be introduced into lower-order modes due to bottom interaction. These low-order modes will then propagate in deep water until encountering the continental shelf. Experimental results from the Arctic Ocean between 25 and 45 Hz suggest such propagation conditions. These results, and their interpretation in the context of a coupled mode study will be presented. Emphasis will be placed on the conditions under which mode coupling will occur, and when it must be considered in prediction and localization problems. The coupled mode model, COUPLE [R. B. Evans, J. Acoust. Soc. Am. 74, 188--195 (1983)], is used as the vehicle for this study. Additional approximation schemes of obtaining a coupled mode result will be explored with the objective of obtaining a faster numerical solution. Comparisons will be made with adiabatic normal mode, and parabolic equations models.