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

4pUW16. Scattering of Sholte waves from pointlike obstacles in unconsolidated sediments.

Eric Smith

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

The scattering of sediment-interface waves from material inhomogeneities or buried objects becomes very simple in the limit that the perturbing obstacle may be considered pointlike, and its internal structure ignored. This limit may provide a computationally efficient means to approximately model complicated environments, in which it can provide the dependence of the target strengths in a multipole scattering expansion on the material parameters of a perturbation, or may be used to efficiently estimate conversion amplitudes among modes within the sediments. The applicability of the pointlike-scatterer limit to the case of compact objects buried in water-saturated sediments was tested with a variety of pulse-echo and quasicontinuous wave swept-frequency sonar apparatus. The values of target strength across a range of frequencies were measured using both techniques, and are compared to calculations. Additionally, the phase which appears in the reflection coefficient at such a perturbing obstacle was derived with the continuous-wave method, from properties of the interference of the incident and reflected waves, and is used to deduce boundary conditions at the reflector. The latter method suggests a novel obstacle-detection and ranging technique that uniquely exploits the directional and phase information present in interface waves.

Standards Committee S3 on Bioacoustics. The current status of standards under preparation will be discussed. In addition to those topics of interest, including hearing conservation, noise, dosimeters, hearing aids, etc., consideration will be given to new standards which might be needed over the next few years. Open discussion of committee reports is encouraged.The international activities in ISO/TC 43 Acoustics, and IEC/TC 29 Electroacoustics, and ISO/TC 108/SC4 Human Exposure to Mechanical Vibration and Shock, will also be discussed. The Chairs of the U.S. Technical Advisory Groups for ISO/TC 43 (H. E. von Gierke), and IEC/TC 29 (V. Nedzelnitsky), will report on current activities of these Technical Committees and Subcommittees, including their most recent meetings. (ISO/TC 108/SC4 met in Prague, Czech Republic in September 1994 and ISO/TC 43 and IEC/TC 29 both met in London, U.K. during November 1994.) SCOPE OF S3: Standards, specifications, methods of measurement and test, and terminology in the fields of mechanical shock and physiological acoustics, including aspects of general acoustics, shock, and vibration which pertain to biological safety, tolerance, and comfort.