Acoustic Scattering from Spheroidal Inhomogeneities

Abstract

An acoustic wave propagating under water experiences fluctuations in phase and amplitude attributable, in the main, to scattering from inhomogeneities arising from variations in the temperature field. Since “patches of thermal inhomogeneity” in the sea are generally regarded as lenticular in shape, it is the purpose of this paper to extend, for both plane and spherical sound waves, contemporary wavefluctuation theory to include the circumstance of spheroidal inhomogeneities. Mean-square amplitude and phase fluctuations are considered for acoustic waves propagating in a statistically uniform medium in which random deviations of the refractive index are small. Large-scale inhomogeneities of arbitrary spheroidal shape are treated, and the influence of transmitter-to-receiver range, acoustic wavelength, and “patch” dimensions on variations in waveamplitude and phase is derived for this general case. Particular attention is given the high-frequency ray limit (Bergmann region) and the low-frequency (Fraunhofer diffraction) region. The significant effects on wavefluctuations of nonspherical inhomogeneities are compared for plane and spherical acoustic waves. [This work was supported by the LMSC Independent Research Program.]