SCATTERING OF LOW-FREQUENCY SOUND BY COMPACT OBJECTS IN UNDERWATER WAVEGUIDES

Abstract

This dissertation considers the two-dimensional problem of the scattering of a monochromatic cylindrical wave by an infinite cylinder embedded in a homogeneous fluid. The exact solution is expressed as an infinite series of cylindrical functions with complex amplitudes determined by the acoustic boundary conditions at the surface of the cylinder. New closed-form uniform asymptotic solutions for soft, hard, impedance, fluid, and solid cylinders are derived for the scattered field when the radius of the cylinder is small compared to wavelength; i.e., the Rayleigh scattering regime. The scattered wave approximation is valid for arbitrary source and observation point positions outside the scatterer. The approximate solution is expressed as the sum of fields due to three linear image sources, which allows physical insight into the scattering physics and suggests analytic solutions to various multiple-scattering problems. When a target is located close to the ocean surface or another reflecting boundary, reflections of the incident and single-scattered waves from the boundary lead to multiple scattering from the target, with the target being insonified by virtual sources. The virtual source concept and the derived asymptotics are employed to develop an analytic and numerically efficient model for wave scattering by a target near an interface.