Effects of seabed elastic properties on sound propagation, reflection and scattering

Shear waves in the ocean floor are frequently neglected in acoustic simulations, where it is computationally convenient to model bottom layers as a higher-density fluid. This approximation does not account for energy exchanged between shear and compressional waves, which can impact sound propagation in the water column. Two approaches that more realistically treat the seafloor as an elastic medium are applied and compared with experimental data collected from two study sites: the Atlantis II Seamount and the South Fork offshore wind farm. In the seamount study, a broadband wavenumber integration model effectively captures phase inversions caused by reflection from sub-bottom layers, and suggests that specific shear speed values may completely eliminate some expected arrivals from a source. In the South Fork study, an elastic parabolic equation method is applied in a range-dependent environment to examine scattering effects. By using the parabolic equation algorithm to generate an incident field, scattering integrals can be computed for environments with greater variation across the spatial domain. Bathymetry and seafloor irregularities corresponding to different sediment types are used as inputs for a scattering integral, illustrating the importance of incorporating the correct shear wave characteristics.