ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2aSA1. Phase-space processing of scattering from a submerged elastic layer.

Raymond J. Nagem

Leopold B. Felsen

Brian J. Collins

Dept. of Aerospace and Mech. Eng., Boston Univ., 110 Cummington St., Boston, MA 02215

In scattering from an insonified submerged elastic layer, whose surface is perturbed with periodic or quasiperiodic variations, the resulting Bragg modes are expected to couple to the leaky modes that can be radiated by the unperturbed smooth layer. If these two distinct but coupled phenomenologies can be separately identified and extracted from acoustic scattering data by ``wave-oriented'' processing, one may gain discriminants for imaging the properties of the elastic layer and of its surface topology. A simple two-dimensional model---a finite array of filamentary scatterers on the insonified face of a fluid layer---has been investigated previously [T. Hsu, L. B. Felsen, and L. Carin, to appear in IEEE Trans. Antennas Propag.]. It has been shown that windowed-transform processing of data observed along a track parallel to the layer extracts space-wave-number phase space distributions in which the leaky mode and Bragg mode footprints are clearly separated; these features are poorly resolved in the unprocessed data. The present paper explores these phenomenologies and the corresponding phase-space processing when the fluid layer is replaced by an elastic layer with its far richer variety of layer-guided modes. Parametric studies show how the space-wave-number distributions are affected by the processing window size, the physical parameters of the layer, and the size and spacing of the filament array.