ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06
5aUW1. Shallow water propagation in the presence of a rough sea surface
and the associated bubble clouds.
Guy V. Norton
Naval Res. Lab., Stennis Space Center, MS 39529-5004
Jorge C. Novarini
Planning Systems, Inc., Slidell, LA 70458
Richard S. Keiffer
Naval Res. Lab., Stennis Space Center, MS 39529-5004
Propagation models in underwater acoustics usually incorporate the
sea-surface roughness as a perturbation, (i.e., a loss mechanism through an
additional attenuation factor) based on coherent loss in the specular
direction. In addition, scattering kernels are generally derived assuming a
homogenous medium underlying the sea surface, an assumption incompatible with a
realistic environment. Using a numerical model [Norton et al., 3018(A)
(1994)] that combines a high-fidelity parabolic equation propagation model with
the conformal mapping technique to handle surface roughness in a marching
algorithm developed by Dozier [L. B. Dozier, 1415--1432 (1984)],
forward propagation under a rough surface can be modeled in a mathematically
consistent way. The technique is applied to the problem of shallow water
propagation in the presence of an inhomogeneous bubble distribution. The ocean
environment consists of bubble plumes in different stages of development. The
effect of the bubbles are introduced through the complex index of refraction.
The model is exercised for frequencies between 20 and 40 kHz. The combined
effect that the rough surface and the inhomogeneous environment has on
amplitude and phase fluctuations and on transmission loss is examined. [Work
supported by ONR.]