Long range, low frequency source localization across the Gulf Stream front using multiple bottom/surface bounce paths observed on a large aperture vertical array: A Bayesian approach

The New England Seamounts Calibrated Acoustic Fluctuation Experiment (NESCAFE) is an ongoing experiment to assess how the New England seamounts and Gulf Stream interact to affect low-frequency ocean acoustic propagation. In a spring 2023 pilot study, two transceiver moorings (East and North) were deployed, on either side of the Gulf Stream and away from the seamounts at a range separation of roughly 153 km. The transceivers sent three consecutive two-minute-long up-down 200–300 Hz FM sweeps every hour, and the signals were recorded on upper/lower arrays nominally from 88 to 343 m and 850 to 1093 m. A total of 23 transmissions from the East mooring were recorded on the North mooring before the East mooring failed. The time front arrival pattern shows roughly 1 s of ducted arrivals followed by 13 s of organized bottom/surface interacting energy. Planewave beamforming reveals 23 arrivals with between 6 and 17 boundary interactions. The 23 observations of received angle and travel time are used in a Bayesian approach to localize the source and gain insight into the propagation physics. The localization was aided by high-resolution shipboard Conductivity, Temperature, and Depth (Fast CTD) measurements taken between the moorings, but one month later.