Abstract:
Biot theory appears to be a viable model for wave propagation in porous ocean sediments, but difficulties in accurately determining the required material parameters leave some interesting predictions based on this formalism in doubt. For example, parameters recently reported for sand sediments off Kings Bay, GA and Panama City, FL [N. P. Chotiros, J. Acoust. Soc. Am. 97, 199--214 (1995)] suggest that Biot's slow wave can be excited in these sediments with a propagation speed high enough to significantly enhance sonar transmission of coherent acoustic wave energy into the bottom at shallow grazing angles. While buried hydrophone measurements confirm higher sound-pressure levels than expected from fluid sediment models, the interpretation of these measurements can be ambiguous. To remove some of these ambiguities, numerical modeling of the scattering by simple targets both in free-field and in buried configurations is suggested. By investigating the scattering by porous targets or elastic targets in a porous background, the dynamics unique to a coupling to Biot's slow wave can act as a fingerprint of this wave's generation. This will be demonstrated with examples calculated using an exact scattering solution of Biot's equations. [Work supported by ONR.]