Using the frequency-difference autoproduct to passively range remote sources in the deep ocean

Signal processing techniques utilizing the nonlinear frequency-difference acoustic-field autoproduct have been applied in recent years to successfully localize remote sources in the shallow ocean [Worthmann et al., JASA 138, 3549–3562 (2015)] and in the deep ocean [Geroski and Dowling, JASA (to appear)] by switching the signal processing to below the signal band frequencies. The successful source localization results obtained here indicates the robustness of frequency differencing techniques to the problem of mismatch between measured and computed acoustic fields that plagues source localization algorithms based on correlating computed and measured field. The promising deep ocean results were obtained by analyzing PhilSea10 experimental acoustic recordings from a water-column spanning vertical array with 149 receivers and an approximate length of 5 km. Given that such an extensive receiving array is unlikely to be routinely available, an investigation was conducted to determine how reduced array aperture and transducer count influence source ranging results from frequency-differencing techniques for 100-Hz bandwidth signals having center frequencies from 170 and 260 Hz, and source to array ranges between 100 and 500 km. Ranging results from this study are presented for both simulated and measured in-band signals, and are calculated using single-digit Hz difference frequencies. [Sponsored by ONR.]