Extracting Green's functions between ships of opportunity using a vertical array.

A theoretical method for estimating the Green's function between two points in an acoustic waveguide was proposed using a vertical source array that spans sufficient waveguide depth [Roux and Fink, J. Acoust. Soc. Am. 113, 1406-1416 (2003)]. This paper shows that by reversing the role of sources and receivers, the Green's function between two ships (sources) can be extracted using a vertical receiver array with a limited aperture. First, the Green's functions from each ship are estimated along the array via blind deconvolution. Then the Green's function between two ships is obtained by either correlation or convolution of the individual Green's functions summed over the array, depending on the array position with respect to the ships. The feasibility of extracting Green's functions between ships of opportunity radiating random broadband (100-500 Hz) noise is demonstrated using a 56.25-m aperture vertical array in approximately 100-m shallow water.