Broadband scattering from spherical shells in a waveguide: modeling and classification

Abstract

In this presentation, the exact expression for scattering from a sphere in a Pekeris waveguide (e.g., Sammelmann and Hackman, J. Acoust. Soc. Am., 𝟠𝟚, 1987) is discussed. The importance of the sphere/interface rescattering terms is considered. A computationally faster multipath expansion approach is derived and its accuracy compared with the exact approach. For sufficiently high frequencies and in the case where the rescattering terms can be ignored, the multipath approach yields accurate predictions. The broadband scattering from an elastic-shelled sphere in a Pekeris waveguide is considered as a function of the frequency (or time for a pulse) and the sphere's range and depth in the waveguide. The classification problem is also discussed. The echos (time series or spectra) from a large set of spheres with varying parameters are generated and grouped into six classes corresponding to the various shell thicknesses and materials. Simple classifiers based upon temporal or spectral representations are considered for the spheres in free space and in a waveguide