Passive characterization of underwater acoustic waveguides through interferometry of diffuse ambient noise

摘要

It was recently demonstrated experimentally that sound-speed profiles in the ocean can be retrieved with oceanographically relevant accuracy from cross-correlation functions of ambient noise recorded on hydrophones separated by O(1)km. To be of practical interest, passive ocean acoustic tomography should work at ranges O(100)km or larger. An extension of passive tomography to such ranges requires retrieval of deterministic travel times or phases of normal modes from cross-correlation functions of imperfectly diffuse noise fields. Here we study diffuse noise fields generated by random sound sources distributed on a surface or in a volume in a horizontally-inhomogeneous waveguide. We show that two-point cross-correlation function of imperfectly diffuse noise field contains the same information about phases and travel times of adiabatic normal modes as would be obtained in a reciprocal transmission experiment, where each noise-recording hydrophone is replaced with an acoustic transceiver. Our theoretical results suggest using noise interferometry for passive acoustic characterization of ocean dynamics.