UC San Diego

Acoustic observations collected by a REMUS 600 autonomous underwater vehicle on the New England Shelf Break show delayed, sloping, and diffuse returns associated with a seafloor depression and the disruption of otherwise persistent sub-bottom stratigraphy. To investigate mechanisms capable of producing the observed scattering features, a two-way coupled normal mode model is developed for an idealized seafloor depression with sloping edges and modified sediment structure. Modes with substantial support near the perturbed sub-bottom structure undergo the strongest redistribution, with strong non-adiabatic coupling including significant forward and backscattering across an array of output modes and angles. Water-column-confined modes generally interact weakly with the leading edge, although they may undergo appreciable backscattering at the trailing bathymetric transition. Full-field calculations illustrate edge-generated forward and backscatter, strong coupling into sediment-associated propagation modes, and reradiation into the water column. Finally, comparison between the data recorded by the autonomous underwater vehicle and the model output confirms that the model has qualitatively demonstrated the mechanisms responsible for the patterns in the data.