Classification of a cylindrical target buried in a thin sand-water mixture using acoustic spectra

Abstract

A number of papers have shown that it is possible to characterize an air-filled cylindrical shell immersed in water using data obtained from a backscattering spectrum. The scattered impulse time signal is constituted of echoes linked to the reradiation of waves circumnavigating around the cylindrical target. In the first part of this work, the scattered signal is calculated and then measured under conditions where the cylindrical shell is immersed in water. In the second part, the cylindrical shell is buried in a thin sand-water mixture. It is insonified perpendicularly to its axis and perpendicularly to the water mixture interface. The scattered impulse time signal is recorded and processed using a Fourier transform algorithm to obtain a resonance spectrum. Among all the resonances that are established in the explored frequency band, only those related to the circumferential S(0) wave are observed on the resonance spectrum of a cylindrical shell buried in the sand-water mixture. Resonances of the circumferential A wave also called A0- wave seem to have vanished. The resonance spectrum obtained by the Method of Isolation and Identification of Resonances (MIIR) reveals that it is possible to detect and classify an object buried in thin sand-water mixture in laboratory conditions.