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Passive acoustic detection of surface ships at ranges exceeding 100 kilometers and mechanisms for ship noise generation

The passive ocean acoustic waveguide remote sensing technique is employed to detect diesel-electric vehicles at ranges exceeding 100 kilometers. The underwater sounds radiated from these vessels are received at long ranges on a large-aperture densely-sampled horizontal coherent hydrophone array. The source levels of these signals are estimated by correcting the received pressure levels for transmission losses modeled using a calibrated parabolic equation-based acoustic propagation model for random range-dependent ocean waveguides. Here we find spectra of ship-radiated sound that is extremely dynamic containing both broadband signals and narrowband tonals at discrete frequencies with source levels that vary depending on ship conditions. We track a vessel with increasing range to find range dependence on broadband signals at close range and tonal signals at long range. Machinery noise generated from engines, propellers, flow noise and other cavitation sources are found to vary depending on ship conditions and are unique to each vessel. Our analysis indicates these vessels can be instantaneously tracked over wide areas spanning more than 300 kilometers in diameter.