Using frequency-differencing to robustly localize distant sources in the deep ocean

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Frequency-Differencing (FD) methods have proven successful for localizing distant sources both in the deep ocean [Geroski and Dowling, J. Acoust. Sci. Am. 146, 4727–4739 (2019)] and in the shallow ocean [Worthmann et al., J. Acoust. Sci. Am., 138, 3549–3562 (2015)]. These source localizing algorithms are based upon matching the phase of a product of measured complex field values, termed autoproducts, to a replica field that is calculated based on the user's knowledge of the environment, similar to Matched Field Processing (MFP). Unlike MFP, FD methods have proven to be robust to the problem of environmental mismatch in ocean environments. Because of the focus on demonstrating robustness to environmental mismatch, these efforts have provided little guidance for a user to apply such methods in the practice. This presentation explores the process of how to choose difference frequencies and difference frequency bandwidths to localize sources at long ranges in the deep ocean, as well as how to use snapshot averaging to improve FD source localization results. These results and limitations are demonstrated using measurements taken in the PhilSea10 experiment from moored sources as far as 450 km away from the vertical receiving array, as well as simulations mimicking acoustic propagation in this environment. [Sponsored by ONR.]