Estimating the influence of ice thickness and elasticity on long-range narrow-band reverberation in an Arctic environment

Abstract

A full-field perturbation approach [A. Ivakin (2016), J. Acoust. Soc. Am., 140(1), 657-665] is modified for an ice-covered ocean and applied to estimating narrow-band long-range reverberation caused by roughness of the ice-water interface. First-order approximation of the approach is used which requires the roughness amplitudes be small compared to the acoustic wavelength. An upward refracting sound speed water column profile typical for Arctic conditions is assumed. To obtain the zeroth-order Green’s function and transmission loss field used in the reverberation model, elastic parabolic equation solutions [J. Collis, S. Frank, et al. (2016), J. Acoust. Soc. Am., 139(5), 2672-2682] are generated in range-independent environments. Ice is represented by two layers. The first approximates acoustic properties of a relatively thin, water-saturated transitional ice layer and is described as a stratified fluid with sound speed increasing with the distance from the ice-water interface. Second layer is introduced as a homogeneous isotropic elastic medium with fixed complex shear and longitudinal wave speeds. Effects of ice properties are discussed and demonstrated by comparing reverberation calculated for different ice layer thicknesses and shear speeds varying from zero (for a fluid model) to typical ice values.