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Communication Dans Un Congrès Année : 2014

DE-COHERENCE EFFECTS IN UNDERWATER ACOUSTCS: SCALED EXPERIMENTS

Résumé

We reproduce, using scaled experiments in a water tank, the effects of scattering phenomena responsible for the degradations of sonar system performances in oceanic environment (typically, the small sound speed fluctuations associated with linear internal waves). We reproduce a wide panel of scattering effects, spanning from " simple " phase aberrations up to radical changes in the sound field structure (appearance of caustics). An experimental protocol was developed. It consists in transmitting a high-frequency wave train (ultrasonic pressure field around 2MHz) through wax lenses with randomly rough faces, that induce distortions comparable to those that would be observed at sea at around 1kHz in the case of a lower frequency acoustic signal travelling through a linear internal wave field. Using a 3-D printer, we were able to manufacture lenses with a randomly rough face characterized by its amplitude and vertical and horizontal correlation lengths. The dependence of the various parameters involved in the experiment (related to the object, distance of propagation, frequency, …) were studied using simulation programs allowing to measure the average number of eigen rays and the phase difference between the extreme micro paths. Those two quantities are useful to compare our results to what was obtained in the literature, in particular to Flatté's dimensionless analysis. The propagation through the lenses was then studied in a water tank using virtual arrays (automatic displacements of a hydrophone). We represent the results using the acoustic envelop in order to observe wave front distortions or appearance of caustics. Measurements of the coherence function and, hence, of the radius of coherence, are carried out. Finally, we observe degradation of the performances of a localization algorithm.
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Dates et versions

hal-01313628 , version 1 (10-05-2016)

Identifiants

  • HAL Id : hal-01313628 , version 1

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Gaultier Real, Jean-Pierre Sessarego, Xavier Cristol, Dominique Fattaccioli. DE-COHERENCE EFFECTS IN UNDERWATER ACOUSTCS: SCALED EXPERIMENTS. UACE2014 2nd international conferences and exhibitions on Underwater Acoustics , Jun 2014, Rhodes, Greece. ⟨hal-01313628⟩
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