Modelling broadband scattering from shelled spheres in a waveguide

The broadband scattering characteristics of a target may be used to distinguish echos from a target of interest from those of clutter. This type of classification is of interest in many sonar applications: ASW, torpedo, surface mines, and diver detection. In a shallow water situation the original sonar pulse and the echo from the target will consist of a sequence of pulses corresponding to the various combinations of incident and backscattered multipath arrivals. For a very shallow target or one close to the seabed, it may be difficult to isolate some of these multipath arrivals. It is expected that these waveguide effects could have a significant effect upon some classifiers. In this paper, we discuss the modelling of scattering of sound from an elastic sphere (shelled, solid, water-filled, etc) which is in a waveguide with an upper surface and a lower seabed. An exact propagation solution is implemented and used to benchmark a ray-expansion solution. The scattered signals for a variety of different sonar pulses and different positions of a spherical target in the waveguide are shown.