A study of the influence of an off-shore rise on low-frequency modal propagation with Arctic surface loss.

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 off‐shore 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. Environmental parameters and source depth will be varied to explore under what conditions mode coupling can be ignored when considering detection and localization problems. Arctic surface loss will be applied to the modeling results to show how mode varying attenuation will affect those results. The coupled mode model (COUPLE) [R. B. Evans, J. Acoust. Soc. Am. 74, 188–195 (1983)], is used as the vehicle for this study. [This work is sponsored by SPAWAR PMW 182‐2.]