### ASA 127th Meeting M.I.T. 1994 June 6-10

## 3pUW10. Acoustic wave propagation in a random, shallow water waveguide.

**D. B. Creamer
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B. J. Orchard
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*U.S. Naval Res. Lab., Code 7127, Washington, DC 20375
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An analysis of acoustic wave propagation in a random shallow water
waveguide is presented, in which deviations of the index of refraction are a
stochastic process. The specific model studied is motivated by the oceanic
waveguide in shallow waters, in which the subbottom sediment leads to energy
loss from the acoustic field, and the stochastic process results from internal
(i.e., density) waves. In terms of the normal modes of the waveguide, the
randomness leads to mode coupling while the energy loss results from different
attenuation rates for the various modes (i.e., mode stripping). Monte Carlo
simulations of stochastic coupled-mode equations are presented [similar to L.
B. Dozier and F. D. Tappert, J. Acoust. Soc. Am. 63, 353--364 (1978)], from
which the average modal intensity (second moments of the field) and the
scintillation index for this model are derived. It is shown that the usual
concept of equilibrium or saturated statistics must be modified. In the context
of an unrealistically simplified model with only two modes, an interpretion is
provided whereby this result is due to the competition between the mode
coupling terms, which redistribute the modal energies, and mode stripping,
which results in an irreversible loss of energy.