Subcritical-Angle Bistatic Scattering Features for Identifying Buried Spherical Targets and Distinguishing Shell from Solid Structure

This study presents a proof-of-concept framework for identifying buried spherical targets and distinguishing shell from solid structure under subcritical-angle incidence with a near-seabed receiver. In the receiver-position–time domain, the parabolic Radon transform (PRT) concentrates the energy of the curved specular-wave trajectory, unlike the straight bottom-reflected wave, into a localized region of the PRT domain, indicating target presence. In the forward-scattering region, shell targets produce frequency-dependent elastic-wave features distinct from solid targets, enabling shell–solid feature extraction. A controlled water-tank experiment using a stainless-steel shell and a SUJ2 solid sphere, both 10 cm in diameter, the shell 6 mm thick, demonstrates feasibility.