Fast computation of time-domain scattering by an inhomogeneous stratified seafloor.

Marine sediment properties exhibit fluctuations on a very wide range of scales in all three spatial dimensions. These fluctuations lead to scattering of acoustic waves. Seabed scattering models that treat such fluctuations are reasonably well developed under the plane-wave assumption. A recent model, called TDSS (time domain model for seafloor scattering), accurately treats the important point-source-point-receiver geometry for generally stratified fluid sediments-important because this is the geometry employed in many seabed scattering measurements. The computational cost associated with this model is very high and scales roughly with the product of mean source-receiver height above the basement to the fifth power and both bandwidth and wavenumber to the second power. Thus, modeling deep ocean scattering from a near sea surface source and receiver is prohibitive at frequencies above a few tens of hertz. A computational approach was developed based on Levin's method of oscillatory integration, which is orders of magnitude faster than standard numerical integration techniques and makes deep ocean seabed scattering computations practical up to many kilohertz. This approach was demonstrated to agree with the narrowband sonar equation in several simple environments in the limit of small bandwidths, but the TDSS model is expected to be valid for a much wider range of environments.