2025_programme: Measurements of seafloor reverberation of very low frequency acoustic waves in western Mediterranean sea; a comparison to GABIM

• Day: June 16, Monday
    Location / Time: C. THALIA at 15:10-15:30
• Last minutes changes: -
• Session: 09. Modeling techniques for underwater acoustic scattering and propagation (including 3D effects)
  Organiser(s): Boris Katsnelson, Pavel S. Petrov
  Chairperson(s): Boris Katsnelson, Sven Ivansson, Pavel Petrov
• Lecture: Measurements of seafloor reverberation of very low frequency acoustic waves in western Mediterranean sea; a comparison to GABIM
  Paper ID: 2292
  Author(s): Iannis Bennaceur, Nathan Ivkovic, 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 seafloor provides the largest contribution to the reverberation level that THALES DMS (TDMS) UWS tries to better predict to improve its sonar performances.\n \nAn at-sea trial took place in the Mediterranean Sea in September 2024, 30 km off French Riviera coast in a deep-water environment. Two boats were involved, one carrying an acoustic source emitting in the [20; 250] Hz frequency band, immersed at 7 meters under the sea-surface, the other conveying a vertical line array composed of 13 hydrophones spaced by 3 m. The maximal acoustic level of the source is beyond 180 dB (ref. 1μPa@1m) omnidirectional. The boats were spaced from few dozen meters, and 1 to 2-seconds long LFM and CW were transmitted to study the acoustic Reverberation Level (RL) in this quasi-monostatic configuration. \n\nThe output of classical, weighted beamforming according to time and elevation angle, on the 1-s long CW at 215 Hz, allows to extract RL according to the grazing angle θ in a range between 25 and 65°. The evolution of RL regarding θ is in good agreement with Fig. 3 from (Holland and Neumann, JASA, 1998) where two regimes are noticeable; lower RL issued from the scattering by the rough interface between the water and the sediments, and higher level issued from sub-bottom sediments volume scattering and scattering from the rough interface between the sediments and the rocky basement.\n\nFinally, the measured bottom scattering strength will be compared to GABIM (Jackson et al., JOE, 2010).
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• Corresponding author: Dr Iannis Bennaceur
  Affiliation: THALES DMS UWS
  Country: France