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Approche numérique et expérimentale de la propagation sonore en environnements océaniques tridimensionnels : application aux problèmes inverses

Abstract : This work deals with the three-dimensional (3D) aspect of sound propagation in shallow-water oceanic environments with respect to inverse problems. Inverse problems in underwater acoustics are based on twodimensional (2D) modeling of sound propagation, hence ignoring the effects of horizontal refraction, referred to as 3D propagation effects. However, the acoustic propagation in shallow-water environments, like the continental shelf, may be affected by 3D effects requiring 3D modeling to be accounted for. An inversion based on a 3D model for more than two parameters at a time becomes prohibitive due to dramatically increased CPU times. The aim of this work is to investigate the importance of the 3D effects with respect to the performance and reliability of the inversion procedures typically applied in problems of underwater acoustics. To this aim, we focus on a wedge-shaped oceanic wave guide. Laboratory scale experiments of long-range acoustic propagation are performed to identify and interpret the 3D effects due to a sloping bottom, as predicted by numerical simulations. A matched-field inversion procedure implemented within a Bayesian framework and based on the exhaustive search over the parameter space is elaborated. The inversion is performed by comparing low frequency acoustic field data, collected along vertical or horizontal line arrays, to replica generated from 2D and 3D parabolic equation codes. The recoverable parameters are identified by means of a sensitivity study of the cost function. In a preliminary step, the inversion performance is investigated on noisy synthetic data in a simple waveguide where 2D codes apply. A ubspace inversion strategy providing significant reduction in CPU times is examined. The inversion in the presence of a sloping bottom is then considered. The feasibility and the limits of an inversion matching replica from a 2D code are explored. This approach, applied on synthetic data, highlights the relevance of using 2D codes at relatively short ranges. An inversion based on a 3D code is thus only needed for the slope, and reasonable CPU times are achieved. On the other hand, important mismatch might occur at farther ranges and 3D modeling is required.
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https://tel.archives-ouvertes.fr/tel-00514915
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  • HAL Id : tel-00514915, version 2

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Alexios Korakas. Approche numérique et expérimentale de la propagation sonore en environnements océaniques tridimensionnels : application aux problèmes inverses. Autre. Ecole Centrale de Lyon, 2010. Français. ⟨NNT : 2010ECDL0010⟩. ⟨tel-00514915v2⟩

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