2025_proceedings: Measurements of sea-floor backscattering strength of very low frequency acoustic waves in western Mediterranean Sea; a comparison to GABIM [1]

• Session: 09. Modeling techniques for underwater acoustic scattering and propagation (including 3D effects)
  Organised by: Boris Katsnelson, Pavel S. Petrov
• Lecture: Measurements of sea-floor backscattering strength of very low frequency acoustic waves in western Mediterranean Sea; a comparison to GABIM [1]
  Paper ID: 2292
  Author(s): Iannis Bennaceur, Nathan Ivkovic, Xavier Cristol, Adrien Rondeau, Benoit Theckes
  Presenter: Iannis Bennaceur
  Abstract: In the context of anti-submarine warfare, active sonar performances depend on the amount of reverberated energy reaching the receiver after the powerful emission from the source. In the Very Low Frequency (VLF) range, the scattering by the sea-floor provides the largest contribution to the reverberation level that THALES DMS tries to better predict. An at-sea trial took place in the Mediterranean Sea in September 2024, 30km off French Riviera coast in a deep-water environment. Two boats were involved, one carrying an acoustic source emitting at 215Hz, immersed at ≈ 7munderthesea-surface, theotherconveyingavertical line array composed of 13 hydrophones spaced by 3m. The center of the antenna was 45 meters below the sea-surface. The boats were spaced from few dozen meters, and 1-second Continuous Waves (CW) were transmitted in order to measure the acoustic Reverberated Level (RL) in this quasi-monostatic configuration. The output of classical weighted beamforming according to time and elevation angle allowed to extract RL according to the grazing angle in a range between 25and65°. Theevolution of the backscattering strength , deduced from RL, regarding is in good qualitative agreement with other measures that also took place in the Mediterranean Sea [2], where a strong decrease appears from ≈ 33°. However, our implementation of GABIM[1], ranwith afirst-guess geoacoustic model for the sea-floor, indicates that scattering from the volumeinhomogeneities is the main contribution to backscattering strength, regardless of . This observation differs from the one made in [2] where scattering by the rough interface between sediments and the harder basement wasthemaincontribution for intermediate grazing angles.
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• Corresponding author: Dr Iannis Bennaceur
  Affiliation: THALES DMS UWS
  Country: France