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

## 3aUW10. Propagation of acoustic waves near an ocean surface with mean flow
inhomogeneities.

**Kai Ming Li
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*Eng. Mech. Discipline, Faculty of Technol., The Open Univ., Milton Keynes
MK7 6AA, UK
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There is considerable interest in the model of underwater sound
propagation in a moving-stratified ocean as it has long been established that
variations in current speed have significant effects on the propagation of
acoustic waves. This is due to the fact that these variations modify the
sound-speed structure. This paper describes a mathematically rigorous method to
study the propagation of acoustic waves in a vertically stratified ocean with a
mean flow. Much of the significant theoretical work in this field makes use of
a high frequency approximation and the so-called plane-wave ansatz. In this
classical method, one substitutes the ansatz into the governing wave equation
in order to determine an approximate solution. The first-order approximation
leads to an eikonal equation that defines the ``rays'' and the second-order
approximation leads to a transport equation that gives the wave amplitude.
However, a different approach is used in this paper. It is demonstrated that
the acoustic pressure can be represented by a twofold Fourier integral. The
sound pressure is then estimated asymptotically by the method of stationary
phase. The solution is particularly useful to provide a better physical
understanding of the problem at much reduced computational cost.