Passive remote sensing through cross‐correlation of nondiffuse ambient noise.

Abstract

Under rather restrictive assumptions about ambient noise field and its sources, it has been demonstrated theoretically by a number of authors that one can retrieve the exact acoustic Green’s function (GF) of an inhomogeneous medium from the noise cross‐correlation function (NCCF). These assumptions are rarely valid for ambient noise in the ocean. In this paper, asymptotic approaches are used to investigate the information content of two‐point correlation functions of ambient noise and their possible use for passive remote sensing of the environment under more general conditions, when there exists no simple, exact, local relation between NCCF and deterministic GFs. For noise sources distributed on a surface or in a volume of a moving or motionless, inhomogeneous fluid, a relation is established between contributions of ray arrivals to NCCF and GFs. A similar relation is derived for contributions to NCCF and GFs due to adiabatic normal modes in a horizontally inhomogeneous waveguide. The impact of nonunifor...