Tomographic inversion of measured crosscorrelations of ambient noise in shallow water using the ray theory

Abstract

Cross-correlation functions of ambient and shipping noise were measured by near-bottom hydrophones in 100 meter-deep water in the Straits of Florida. This paper is based on cross-correlations in the 20-100 Hz frequency band between two hydrophones 5 km apart. The propagation conditions between the hydrophones were nearly range-independent. The noise cross-correlation functions provides an approximation to the deterministic Green's functions, which describes sound propagation in opposite directions between the hydrophones. Using a background sound-speed profile, 44 eigenrays were found and relevant perturbation matrices were calculated for propagation with and against the flow. Modelled Green's function has 10 peaks, which have been matched to the peaks of the cross-correlation function. Sound speed and flow velocity profiles in water have been retrieved by minimizing the mismatch between positions of the modelled and measured peaks. Acoustic frequencies being low, errors in raytheoretical modeling limit the accuracy of the sound speed profile reconstruction. However, due to the reciprocity principle, the current velocity profile inversion can be done.