ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

5pUW9. Characterizing nonadiabatic ocean acoustic environments.

R. L. Field

T. H. Ruppel

M. K. Broadhead

Code 7173, Naval Res. Lab., Stennis Space Center, MS 39529-5004

In range-dependent environments, the adiabatic assumption, which neglects discrete mode coupling, is often made. Up continental shelves and in shallow-water regions, abrupt changes in the environment make this assumption suspect. An issue in these environments is the degree to which the adiabatic assumption is valid. Transmission loss calculations using both a parabolic equation and coupled mode models show, that for steep slopes, much more energy reaches the shelf from deep water than predicted by the adiabatic approximation. This increase in shelf energy is shown to be due to discrete mode coupling. In this study, changes in energy flux with range are used as a criterion for when the adiabatic assumption breaks down. The flux is computed from a parabolic equation model in upslope environments as a function of range; frequency, and slope angle. It is shown that rapid flux variations are good predictors of when the adiabatic approximation breaks down and mode coupling becomes significant. [Work supported by ONR, Program Element 602435N, with technical management provided by the Naval Research Laboratory.]