Interference structure in the form function for bistatic scattering from elastic spherical shells in water

Abstract

Although the monostatic scattering from a sphere is independent of viewing angle, the bistatic frequency response contains rich structures a function of scattering angle. The exact solution for the far-field scattering from underwater elastic spherical shells is examined as a function of scattering angle. The high-frequency scattering from spherical shells includes contributions from leaky Lamb-type waves that circumnavigate the shell while continuously radiating into the fluid. The form function in scattering angle contains multiple interference patterns between the specular reflection and the different modes of Lamb waves. This interference structure is similar to the case for solid spheres and cylinders recently studied [A.M. Gunderson, A.L. Espana, and P.L. Marston, J. Acoust. Soc. Am. 142, 110–115 (2017)], where the interference patterns between the specular reflection and Rayleigh waves were examined. For the elastic shell case, the greater number of Lamb wavemodes and their highly dispersive nature creates richer interference structure in the form function from that of the solid sphere. The interference loci between the specular reflection and the two lowest mode Lamb waves are calculated and compared with the bistatic form function. [Work supported by the Office of Naval Research.]