2023_programme: Acoustic travel times, transmission loss, and ambient sound observed on a tomographic array in the Beaufort Gyre during 2016–2017

• Session: 01. Acoustics in polar environments
  Organiser(s): Jaroslaw Tegowski, Philippe Blondel and Hanne Sagen
• Lecture: Acoustic travel times, transmission loss, and ambient sound observed on a tomographic array in the Beaufort Gyre during 2016–2017 [invited]
  Paper ID: 2055
  Author(s): Worcester Peter, Dzieciuch Matthew, Vazquez Heriberto, Cornuelle Bruce, Colosi John, Krishfield Richard, Nash Jonathan
  Presenter: Worcester Peter
  Abstract: The Arctic Ocean is undergoing dramatic changes in response to increasing atmospheric concentrations of greenhouse gases. The 2016–2017 Canada Basin Acoustic Propagation Experiment (CANAPE) was conducted to assess the effects of the changes in the sea ice and ocean structure in the Beaufort Gyre on low-frequency underwater acoustic propagation and ambient sound. An ocean acoustic tomography array with a radius of 150 km that consisted of six acoustic transceivers and a long vertical receiving array measured the impulse responses of the ocean at a variety of ranges every four hours using broadband signals centered at about 250 Hz. The peak-to-peak low-frequency travel-time variability of the early, resolved ray arrivals that turn deep in the ocean was only a few tens of milliseconds, roughly an order of magnitude smaller than observed in previous tomographic experiments at similar ranges, reflecting the small spatial scale and relative sparseness of mesoscale eddies in the Canada Basin. The high-frequency travel-time fluctuations were approximately 2 ms rms, roughly comparable to the expected measurement uncertainty, reflecting the low internal-wave energy level. The implication is that long temporal processing and near-optimal pulse compression gains should be possible, although internal-wave energy levels may well increase in the future as the ice extent continues to decrease and allows additional wind forcing. The transmission loss was less than would have been expected at 250 Hz based on measurements made prior to the recent changes in the Arctic. It increased as the ice draft increased, with rays experiencing more surface reflections showing greater transmission loss, as expected. Low-frequency ambient sound levels showed a strong seasonal modulation, although with considerable variability from day to day. These results are generally consistent with the Thin-ice Arctic Acoustic Window (THAAW) hypothesis proposed roughly a decade ago.
• Corresponding author: Dr Peter Worcester
  Affiliation: Scripps Institution of Oceanography, University of California San Diego
  Country: United States
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