Acoustic scattering in an elastic medium as it relates to sea ice and the determination of effective moduli

Abstract

The scattering of sound in ice is a complex problem which depends upon the material properties of the ice as well as the frequency of the sound source. Because of the complexity of the problem, a simplified approach to acoustic wave scattering is taken. The ice is modeled as a two-phase medium in which fluid-filled cylindrical cavities (brine channels) are embedded in an attenuating elastic matrix. An analytical solution is obtained for the acoustic scattering of longitudinal waves from an infinitely long cylinder. The solution is extended for low-ka wave propagation in order to determine effective moduli (Lamé parameters and density) and effective wave speeds. An experiment is conducted in the lab to determine the scattering cross section versus angle for a single cylindrical scatterer for frequencies of 160 and 200 kHz. In addition, effective moduli are determined as a function of cavity concentration. The experimental and theoretical results are presented. [Work supported by ONR.]