Pulse Scattering on an Ice Sphere Submerged in a Homogeneous Waveguide Covered with Ice

Abstract

The paper is devoted to modeling of the backscattered field from a spherical target immersed in a homogeneous waveguide covered with ice. A bottom of the waveguide and an ice cover are fluid, attenuating half-spaces. A target is assumed to be acoustically rigid or fluid. In particular, the properties of the ice cover and a scatterer may coincide. The emitted signal is a pulse with a Gaussian envelope. The normal mode evaluation is applied to the scattering coefficients of a sphere. The amount of normal modes forming the backscattered field is determined by a given directivity of the source. Computational results are obtained in a wide frequency range 8–12kHz for water depths equal to several hundreds of meters, and distances between a source/receiver and a target from 1km up to 10km. It is shown that in a range interval up to several kilometers the backscattered field can be calculated also using a simplified medium model consisting of a water half-space and an ice half-space. In this case the scattering coefficients of a sphere are evaluated by the steepest descent method. For the considered oceanic waveguide of 200m depth with a sandy bottom the use of the simplified medium model essentially shortens a computing time.