Abstract
Noise interferometry relies on averaging long time series to reveal the deterministic features of the noise cross-correlation function, which contain information about the propagation medium. Unlike the solid earth, the ocean exhibits considerable variability at the time scales that are shorter than the necessary noise averaging times of hours and days. This variability is a primary factor that limits useful noise averaging times and underlies the more limited applicability of acoustic noise interferometry than of the better established seismic interferometry. This paper aims to quantify the restrictions, which are imposed on the noise interferometry by the ocean variability, and to identify possible applications of passive acoustic remote sensing to characterizing ocean dynamics. A theory will be presented that quantifies the coherence loss of measured noise cross-correlations due to gravity waves on the ocean surface, tidally induced changes in the water depth, and internal gravity waves. It is found that temporal variations of the ocean parameters lead to frequency-dependent suppression of deterministic features in the noise cross-correlation functions. The coherence loss limits the resolution of deterministic inversions. On the other hand, the passively measured coherence loss can be inverted to statistically characterize ocean dynamics at unresolved spatial and temporal scales.
Published Version
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