A METHOD FOR ACOUSTIC SCATTERING BY SLENDER BODIES .1. THEORY AND VERIFICATION

This paper presents a new approach for calculating sound scattering by slender scatterers. The method is based on the assumption that the so und scattering function can be approximated by superimposing the scatt ered waves from a series of small adjacent cylindrical elements, with each of these elements scattering sound as though it were part of an i nfinite straight cylinder of the same radius. Using the Kirchhoff inte gral theorem, the bistatic scattering function is derived rigorously w ithin the accuracy of the assumption. To validate the approach, the so lution is applied to sound scattering by fluid prolate spheroids, for which the exact solution is known. Numerical comparison with the exact solution reveals that the new approach is very versatile; it can pred ict scattering patterns remarkably comparable to that obtained by the exact solution for a wide range of incident angles. For incidence with in approximately +/-20 degrees of the broadside direction, the scatter ing patterns predicted by the new method coincide uniformly with the e xact results. Agreement in the absolute scattering amplitude slowly de teriorates as the incidence is tilted away from the broadside aspect. However, the method consistently produces scattering patterns highly c orrelated to the results from the exact solution; this is potentially useful for target identification based on pattern recognition techniqu es. The results also show that the new method works better on the whol e as the elongation of the target increases. Furthermore, calculation of cross-correlation coefficients indicates that the present method wo rks slightly better for rigid bodies than for weak fluid bodies. The l ow-frequency scattering by gas-filled spheroids is also considered. It is shown that near resonance the scattering is almost isotropic, in a greement with the prediction of previous simple analytic solution. (C) 1997 Acoustical Society of America. [S0001-4966(97)02109-7]PACS numbe rs: 43.20.Fn, 43.20.Tb, 43.30.Gv [JEG].