Random-bottom structural effects on shallow-water sound transmission using a modified ray theory

Abstract

A modified ray theory is used to study the effects on acoustic intensity of randomness in bottom structure. A shallow isospeed ocean channel with horizontal boundaries is assumed. The randomness is produced by stochastic variations in the bottom density and sound speed in the horizontal direction beneath the water–bottom interface. Beam and time displacements at the ocean bottom are incorporated into each acoustic ray. Ray geometry, spreading loss, and bottom loss are analyzed in order to obtain expressions for the mean and variance of intensity at a point receiver for a transmitted cw signal. Formulas are sufficiently general to permit their use with different bottom-acoustic models of sound reflection. In order to incorporate bottom attenuation simply, Mackenzie theory is employed here. The distinctive acoustic consequences of bottoms of different density mean and horizontal correlation are discussed. In addition, comparisons of results using the modified ray theory and standard ray theory are provided. Also, intensity moments are described for differing source–receiver range, water depth, and acoustic frequency.