Application of elastic parabolic equation solutions to calculation of acoustic reverberation in ice-covered underwater environments

Abstract

Parabolic equation solutions can be obtained for underwater acoustic environments where elastic boundaries affect the acoustic propagation. One example of this situation is in the Arctic where a (potentially rough) ice layer is on top of the water column. The elastic parabolic equation method shown here rigorously applies both the zero-traction and fluid-elastic interface boundary conditions to obtain full field Green’s function estimates of the complex acoustic field near the ice-water interface. This solution is crucial for calculation of recently derived reverberation estimates that require both horizontal and vertical derivatives of the complex acoustic field. Monostatic reverberation estimates for a rough under-ice interface are calculated for an upward refracting water sound speed profile and an elastic ocean bottom with a nearly fluid mud layer. Comparisons are made between reverberation from a fluid model ice layer and elastic model ice layer. These calculations are used to demonstrate how variations in ice layer material parameters affect reverberation and could be used, for example, to estimate areal distribution of the ice layer roughness from azimuth-time dependence of acoustic reverberation measured in Arctic environments.