Width estimation of a subsurface water-filled crack using internal multiple reflections from electromagnetic scattering model of a cylinder

A width estimation method for a subsurface water-filled crack using internal multiple reflections is proposed. The energy transport and path length of internal multiple reflections are analyzed from electromagnetic scattering model of a dielectric cylinder using the extended ray theory. The energy transport shows that some multiple rays transport along the surface of the cylinder to the receiver, which form the creeping waves, and some multiple rays refract toward the receiver, focusing on the radial direction. The conclusion that the path lengths are multiples of a diameter distance is utilized to estimate the width of the cylinder. In order to distinguish the adjacent reflections with small time interval, wavefronts and resonances of internal multiple reflections are also analyzed, based on the fact that the creeping waves and refracted waves at the radial direction show different resonances in the time-frequency domain. In order to verify the proposed method, experiments both in free space and subsurface scene are given to estimate the width of water-filled cracks.