Spatial-Correlation Functions for Various Noise Models

Abstract

Observations indicate that noise in the ocean is a superposition of an isotropic noise field and an anisotropic noise field originating at the surface. Models which produce such noise fields are described, and the spatial-correlation functions are obtained. The volume-noise model, which produces an isotropic noise field, consists of noise sources uniformly distributed within a sphere. A single-frequency component of each noise source is considered; the mean-square output of each is the same, the relative phases are random, and inverse spreading occurs. It is shown that for a very large sphere the spatial correlation is the same as that given by Marsh for a homogeneous isotropic noise field and by the Faran and Hills noise model, which consists of noise sources on the surface of a large sphere. The surface-noise model consists of noise sources uniformly distributed on a large circular area of a plane. The noise sources are assumed to be directional, in addition to having the properties listed above. The spatial correlation is obtained as a function of the directionality of the noise sources, the spacing of the receivers and their orientation with respect to the surface, and the electrical delay.