| Summary: | The backscattering of sound by inhomogeneities of the ocean sediment may provide
a remarkable effect on underwater acoustic wave propagation. It may also be used
as a means of remotely estimating complicated sediment properties. In this paper, a
theoretical model of acoustic waves backscattered from an inhomogeneous sediment is
formulated based on the Born approximation. The model not only contains the formal
homogeneous bottom case but is also extended to the more realistic stratified bottom
case. A complex wavenumber, in which an attenuation coefficient is introduced, reveals
significant changes of the penetration depth within the sediment.
The model predicts that for the stratified bottom, the backscattering strength is
rapidly oscillating and decreases sharply at small grazing angles owing to the refraction
of the waves caused by the sound velocity gradient.
In order to reduce the number of independent variables, Biot's theory is applied
to relate three-dimensional density fluctuations to sound speed fluctuations through
porosity. A transverse-isotropic model is also developed to access the three-dimensional
sound speed fluctuation spectrum.
Geoacoustic surface and cross-hole tomographic data acquired from different sites
characterizing sandy and silty bottoms are used to obtain three-dimensional sediment
volume inhomogeneities. Backscattering strengths are evaluated for those bottom cases.
The results agree with intuition and other published data.
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