Estimation of source depth from low-frequency acoustic transmissions through the Gulf Stream

The New England Seamounts Calibrated Acoustic Fluctuation Experiment (NESCAFE) is an ongoing experiment supported by ONR to assess how the New England seamounts and Gulf Stream interact to affect low-frequencyunderwater acoustic propagation. In a spring 2023 pilot study, two transceiver moorings were deployed, on either side of the Gulf Stream and away from the seamounts at a range separation of 153 km. The transceivers sent three consecutive 2-min-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. Due to strong currents, one of the sources designed to be at a depth of 1100 m, was pulled down close to a depth where the mooring buoyancy could fail. A total of 23 transmissions were recorded from this source before the mooring did fail and the aim of this talk is to present source localization estimates derived from the receptions made 153 km away. The localization was aided by high-resolution shipboard Conductivity, Temperature, and Depth (Fast CTD) measurements taken between the moorings but 1 month after the failure. This talk will also investigate the impact of sound-speed profile uncertainty in determining the source depth.