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

## 5pUW9. Characterizing nonadiabatic ocean acoustic environments.

**R. L. Field
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T. H. Ruppel
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M. K. Broadhead
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*Code 7173, Naval Res. Lab., Stennis Space Center, MS 39529-5004
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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.]