Seabed rough surface scattering described by 2-way coupled mode approach

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 K_L 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 K_L and large h values. However, for large K_L 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/K_L (a correlation distance) in the physics of multimodal scattering from a rough seabed in shallow water.