Experimental active source ocean acoustic interferometry.

Abstract

Green’s function approximation via ocean noise cross-correlation, referred to here as ocean acoustic interferometry, has previously been demonstrated experimentally for passive noise sources. Active sources offer the advantages of higher frequencies, controllability, and continuous monitoring. Experimental ocean acoustic interferometry is described here for two active source configurations: a source lowered vertically, and one towed horizontally. Results are compared and contrasted with cross correlations of passive noise. The results, in particular differences between the empirical Green’s function estimates and simulated Green’s functions, are explained with reference to theory and simulations. Approximation of direct paths is shown to be consistently good for each source configuration. Secondary (surface reflection) paths are shown to be more accurate for hydrophones with a greater horizontal separation. [Work supported by the Office of Naval Research under Grant No. N00014-05-1-0264.]