10: Emergence of the Greenâ•Žs Functions from Noise and Passive Acoustic Remote Sensing of Ocean Dynamics

LONG-TERM GOALS • To evaluate feasibility and determine physical limits of performance of a passive acoustic system for characterization of a time-varying ocean where ambient acoustic noise is utilized as a probing signal. • To develop a passive remote sensing technique for acoustic characterization of oceanic currents. OBJECTIVES 1. To demonstrate theoretically emergence of the deterministic Green's functions (GFs) from cross-correlations of noise due to sources distributed in a volume and on boundaries in inhomogeneous, fluid-solid environments with dissipation. 2. To investigate a relation between the deterministic GFs and a two-point correlation function of noise in a low-frequency regime where stationary-point arguments become inapplicable. 3. To quantify degradation of performance of passive remote sensing techniques due to ocean surface motion and other variations of underwater sound propagation conditions in time. 4. To retrieve flow-induced non-reciprocity of acoustic phase and amplitude of the deterministic GFs from cross-correlation of diffuse sound fields generated as a result of scattering by inhomogeneities in the water column and/or by seafloor and sea surface roughness. 5. To determine accuracy of current velocity measurements using acoustic travel time non-reciprocity retrieved from a two-point noise cross-correlation. 6. To evaluate, for shallow-and deep-water scenarios, optimal parameters of a passive acoustic system for ocean temperature and current velocity measurements using cross-correlation of ambient noise and/or sound fields generated by sources of opportunity.