Observations of acoustic intensity and phase fluctuations for low-frequency acoustic transmissions through the Gulf Stream

The New England Seamounts Calibrated Acoustic Fluctuation Experiment (NESCAFE) is an ongoing research effort to understand low-frequency (250 Hz, 100 Hz bandwidth), long-range (100–200 km) acoustic propagation in the presence of strong Gulf Stream fronts. In a pilot experiment conducted in the spring of 2023, 23 FM-sweep acoustic transmissions were received by a 60-element vertical line array 153 km from the source. The acoustic path between the source and the receiver crossed the Gulf Stream from the Sargasso Sea to the Slope Sea. In this talk, fluctuations in the acoustic intensity and phase along identified wavefronts will be quantified and presented. A high-resolution ship-board measurement of range-dependent temperature and salinity along the track between the source and the receiver—taken 1 month after the transmissions—is utilized for ray-based wavefront identification. The observed fluctuations in acoustic intensity and phase will be compared to predictions from internal wave acoustic scattering theory based on the ΛΦ method. Lastly, the relevance of these findings to the full NESCAFE experiment (conducted between June 2024 and June 2025) will be discussed. Work supported by ONR.