5pUW16. Frequency-dependent classification cues resulting from localized interactions on a target surface.

Session: Friday Afternoon, December 6

Time: 5:20

Author: Gregory Kaduchak
Location: Appl. Res. Labs., Univ. of Texas, P.O. Box 8029, Austin, TX 78713-8029
Author: Charles M. Loeffler
Location: Appl. Res. Labs., Univ. of Texas, P.O. Box 8029, Austin, TX 78713-8029


Much work has been done to extract information about a scatterer by analyzing the spectrum of its echo return. Typical applications rely on phase matched circumnavigations of a surface guided wave (a ``resonance'' of the structure). The present research incorporates high-frequency scattering mechanisms which interact in a small localized area located about the specular points of a curved surface. The scattering contributions from such mechanisms promptly follow the onset of the specular echo in the time signature and are independent of the backside of the scatterer. The mechanisms presented here include the effects of thickness resonances and ``negative'' group velocity surface guided waves. It is shown that by temporally isolating the region about the specular return in the backscattered time signature, it is possible to gain information related to the thickness and/or material properties of a scatterer. This is demonstrated both computationally and in experiments involving cylindrical shells and finite surfaces with one- and two-dimensional curvature. The scatterers are constructed from either anisotropic, fiber-reinforced plastics or metals. Experimental results display the ability to probe the thickness of an extended target with high-resolution sonar. [Work supported by ONR.]

ASA 132nd meeting - Hawaii, December 1996