### ASA 125th Meeting Ottawa 1993 May

## 1pAO3. Modeling acoustic propagation in shallow range-dependent
environments.

**R. A. Stephen
**

**
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*Dept. of Geol. and Geophys., Woods Hole Oceanographic Inst., Woods Hole,
MA 02543
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``Shallow'' water means water depth less than an acoustic wavelength and
implies by definition strong interaction with the bottom. However since most
ocean bottoms are rough and laterally heterogeneous many of the assumptions
used to simplify the elastodynamic equations are invalid. On the other hand,
since the depths and ranges of interest are considerably less (in terms of
wavelengths) than deep water problems, direct numerical solutions of shallow
water problems are quite tractable. Finite difference approaches, for example,
have the following advantages over alternative methods: (a) They include all
shear wave (rigidity) effects in the bottom including body and interface waves.
(b) They can be applied to pulse beams at low grazing angles (less than
20(degrees)). (Methods based on ``infinite plane waves'' have conceptual
problems at low angles.) (c) Both forward scatter and backscatter are included
in the solutions. (d) Multiple interactions between scatterers are included.
(e) Arbitrary range-dependent topography and volume heterogeneity, can be
treated simultaneously in the same formulation. (f) Problems are scaled to
wavelengths and periods so that the results are applicable to a wide range of
frequencies. (g) The method considers scattering from structures with length
scales on the order of acoustic wavelengths.