2pPAb7. Distorted-wave Born approximation analysis of sound levels in a refractive shadow zone.

Session: Tuesday Afternoon, May 14

Time: 2:45

Author: Kenneth E. Gilbert
Author: Xiao Di
Author: Rodney R. Korte
Location: Appl. Res. Lab. and the Graduate Program in Acoust., Penn State Univ., P.O. Box 30, State College, PA 16804


Measurements made by Havelock et al. show that above a few hundred Hertz, the sound levels in a refractive shadow zone are weakly dependent on frequency. Parabolic equation calculations made recently by Di and Gilbert indicate that the weak frequency dependence is consistent with scattering from small-scale turbulence governed by a Kolmogorov spectrum. In this paper a theoretical analysis is presented using the distorted-wave Born approximation (DWBA) to show why the Kolmogorov spectrum leads to the observed weak frequency dependence. Using DWBA, the problem of scattering by turbulence is formulated in terms of a sampling function that shows the physical origin of the frequency dependence by showing what part of the turbulence spectrum contributes in a typical measurement of levels in a refractive shadow. Results from the DWBA analysis are compared with the data of Havelock et al. and with parabolic equation calculations. [Work supported by the Army Research Laboratory and the Applied Research Laboratory.]

from ASA 131st Meeting, Indianapolis, May 1996