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A 2-way integral equation coupled mode (IECM) approach is used to examine the physics of scattering from a rough seabed. Roughness realizations for the seabed are generated from a wavenumber power spectrum whose parameterization includes a roll-off wavenumber KL and a root mean square (rms) roughness height h. For the waveguide, source depth, frequency, and seabed type examined, large losses can occur due to scattering of low angle modes into the modal continuum. This occurs for small KL and large h values. However, for large KL and small h energy lost from the trapped modes to the continuum and backscattering can be less than the energy saved by a transfer of energy within the trapped spectrum to the lower order modes with smaller attenuation. The study suggests a critically important relationship between the modal interference distances and 1/KL (a correlation distance) in the physics of multimodal scattering from a rough seabed in shallow water. [ABSTRACT FROM AUTHOR]

The Shallow Water 2006 ocean acoustics experiment on the New Jersey continental shelf was designed in part to determine the frequency dependence of sound speed and attenuation for a sandy sediment in the 50-3000 Hz band. Two acoustic arrays in L-geometries were positioned about 25 km apart on a ridge of coarse sand. Segments of narrowband and impulsive acoustic data were analyzed for the information they contain on the seabed geoacoustic structure and the frequency dependence of the top sediment layer attenuation. The results clearly demonstrate a nonlinear frequency dependence of the absorption. [ABSTRACT FROM AUTHOR]