ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

4aPAa5. Rays, modes, and spectra: Footprints in phase space.

Leopold B. Felsen

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

Ray methods have been used extensively to describe mid- and high-frequency, as well as pulsed, phenomena associated with acoustic propagation in the presence of submerged solid or layered elastic structures. The relevant wavefields include externally reflected and diffracted, as well as externally--internally coupled, progressing constituents, repetitive multiples of which combine into oscillatory (modal) forms. Full exploitation of ray methods for radiation and scattering scenarios, either forward (for classification) or inverse (for identification), is aided by systematic footprinting of the (space-time)--(wave number-frequency) characteristics of the various wave objects in a (configuration)--(spectrum) phase space catalog. ``Clean'' footprints obtained from forward asymptotics for certain test problems are shown to be diffused (a) by windowed processings that are applied to extract these footprints from data (imaging), and (b) by space-time limits imposed on the data set. Examples include submerged elastic cylindrical, and finite flat plate, geometries. Also included are simple models of truncated strict or perturbed periodicity, with illustration of superresolution and backpropagation [L. Carin et al., J. Acoust. Soc. Am. (submitted)]. [Work supported by ONR and AFOSR.]