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

2aUW3. Appearance of elastic wave contributions in high resolution acoustic images.

Gregory Kaduchak

Chad M. Wassmuth

Charles M. Loeffler

Appl. Res. Labs., Univ. of Texas, P.O. Box 8029, Austin, TX 78713-8029

Studies involving plane wave scattering by finite cylindrical shells at oblique incidence display monostatic echo contributions from surface elastic waves. These waves follow helical paths along the shell's surface and are guided back in the source direction after reflection from the cylinder truncation [X.-L. Bao, 1461--1465 (1993)]. The present research examines such effects viewed in the time record of a high resolution sonar system. The target consists of a finite cylindrical shell with a radius to thickness ratio of 5%. The shell is immersed in water and is subject to both exterior and interior fluid loading. It is ensonified with short tone bursts of narrow beam width over a range of incidence angles 90(greater than or equal to)(phi)(greater than or equal to)50, where (phi) is measured relative to the cylinder axis. The backscattered echo signature exhibits prominent artifacts as a result of scattering processes involving the s[sub 0] and a[sub 0] Lamb waves interacting with the cylinder truncation. The echo contributions are extremely sensitive to the angle of incidence and interior fluid loading which may assist in target classification schemes.