Abstract
The Helmholtz–Kirchhoff integral is applied to model the penetration of sound waves into sandy seafloors at grazing angles above and below the critical angle. Although the conditions for the validity of the Kirchhoff approximation can be limiting, this approximation should be valid at high frequency for gently undulating seafloor surfaces even at moderate to low grazing angles, providing that the self-shadowing effect is carefully removed. The analytical development of the method is first presented, followed by numerical examples and comparisons with the experimental data of Maguer et al. [SACLANTCEN report, SR-287, April 1998]. The model predicts, in agreement with the 2- to 15-kHz acoustic data, the frequency where the contributions due to roughness effects begin to dominate those due to the evanescent wave. Secondary effects such as Bragg interference patterns and the loss of signal coherence with grazing angle or depth are correctly predicted. The model simulations strongly suggest that roughness of the sediment interface is most likely the cause of anomalous sound penetration into the seabed.
Published Version
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