UACE2017 Proceedings: ALMA 2014: Observations of multiple sound scattering from random inhomogeneities transported by a mean flow

• Session:
  Design of new experimental facilities to address future problems in underwater acoustics
• Paper:
  ALMA 2014: Observations of multiple sound scattering from random inhomogeneities transported by a mean flow
• Author(s):
  Xavier Cristol, Gaultier Real, Dominique Fattaccioli, Bruno Chalindar
• Abstract:
  The very first sea trial of DGA TN’s modular ALMA system (Acoustic Laboratory for Marine Applications) occurred in October 2014, over the Eastern Corsican shelf (water depth about 85m). The almost motionless system consisted in a source located at about 7km of a 2D array of 64 receivers (about 2m x 2m). The summer configuration involved a strong thermocline emphasizing contributions of bottom reflections of sound, combined with an exceptionally flat sea surface. There was no other significant ensemble movement than a littoral current oriented from the source toward the receiving array. Despite this stationary configuration, interesting Doppler shifts were observed when analyzing transmitted long continuous sinusoidal waves (20 s length), simultaneously at several frequencies (2, 5, 7, 11 kHz). We did not only witness an intuitively predicable spectral broadening of the signals, but also measured constant frequency shifts, depending on the transmitted frequency and stable over two hour and a half. We interpret these phenomena as arising from multiple scattering by moving random inhomogeneities transported by the current (about 0.1m/s). For supporting this interpretation, a time domain extension of Tatarskii’s delta-correlation formalism is proposed, based on the estimations of the first and second moments of the solution to a Time Domain Parabolic Equation.
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Contact details

• Contact person:
  Dr Xavier Cristol
• e-mail:
  
• Affiliation:
  Thales Underwater Systems
• Country:
  France