Arctic Ice Attenuation Model Study : Final Report

Underwater acoustic propagation in the Arctic Ocean is characterized by a refractive surface-channel with a rough boundary. Scattering estimates based on freesurface theory have proven low by more than a factor of two in forward-scatter loss and low by 20 dB or more in backscatter strength. Failure to account for either attenuation or backscattering indicates that impedance effects must be involved. The ice layer is modeled as a uniform elastic solid. Perturbation analysis shows scattering from slopes as well as displacements. Displacements produce piston-like rereradiation in addition to the usual vertical-dipole type associated with free surfaces. The "rocking" horizontal dipole produced by slopes is evidently a significant mechanism at the lower frequencies. However, estimates of both attenuation and backscatter strength are much too low compared with experimental data.