Acoustic Signal Fluctuations in a Simulated Random Medium

Abstract

A statistical study has been conducted under controlled laboratory conditions of sound-wave fluctuations inherent in underwater acoustic propagation through a random (in space) medium. Large (with respect to acoustic wavelength) inhomogeneities of equal volume were formulated, using spherical, liquid-filled neoprene balloons, and the refractive indices (relative to water) of the fluid spheres were arranged on the order of unity with deviations up to 1%. (Such weak, large-scale refractive variations are representative, in part, of circumstances in the ocean.) A large number of these balloon inhomogeneities were suspended underwater at random in an experimental acoustic chamber. Signal fluctuations were measured at four different acoustic frequencies and transmitter-to-receiver ranges within the simulated random medium. For each range frequency combination, numerous ensembles were obtained by rotating the fixed transmitter-to-receiver line of sight about its midpoint. The experimental arrangement and procedures involved in the study are discussed, and a comparison is made between laboratory results and extant theoretical treatments. [Work supported by the Lockheed Independent Research Program.]