Analysis and representation of sonar echo returns

Active acoustic classification of underwater targets is an important problem of current interest. The echo return of such objects has components related to such distinct dynamical elements as the specular (geometric) return, reradiation of elastic resonances, diffracted (or Franz) waves, etc. The arrival times and spectral content of these components will generally give information about the structure and geometry of the scatterer. This information is reflected to the time- frequency structure of the echo return. In this paper, a comparative study is presented of the time-frequency analysis capability of a number of tools in applications to the echo structure of finite elastic cylinders. The time-frequency tools considered include the Wigner-Ville distribution, the Choi-Williams distribution, the Gabor transform, and the continuous wavelet transforms. The comparison is based on echo returns that have been synthesized from numerical T-matrix solutions to the associated free-field scattering problems.