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Theses

Inversion géoacoustique temps réel de signaux large bande par grands fonds

Abstract : This thesis describes the development of a real time geoacoustic inversion method devoted to broad band signals. Aim of this method is to automatically infer geoacoustic bottom characteristics from transmission sound field pressure measurements in a deep ocean medium. Finality is to inform sonar operational team about the parameters of the bottom, so that it can improve the performance evaluation of their acoustic sensors. This work provides useful experience for the design of the future prototype of acoustic REA (Rapid Environment Assestnent). Validation of the concept takes place in this thesis after the implementation of a global step of inversion based on the matching of transmission measured impulse responses and the impulse responses simulated by a ray model able to take into account bottom parameters. Two stages of inversion are necessary. A first one to find the experimental configuration, then another one to determine bottom characteristics. This inversion method is applied in a quasi-automated way to a complex synthetic data set, generated by a real time simulator of the acoustic transmitted signal. Tests on synthetic data set first validate the feasibility of the method and its performances in term of detection of a horizontal transition of the porosity, and in respect of the operational time consuming constraint. It allows to describe also Doppler effect impact on the inversion performances. The method is then successfully tested on acoustic and environmental data set recorded by the Military Center of Oceanography of the EPSHOM in deep water, unfavourable case for the inversion because of the weak informative contents of the signals. The taking into account of a bottom evolutive model in the method of inversion makes it possible to reverse an evolutive medium (with the distance) and to synthesize all the inversion results of atypical campaign of REA.
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Submitted on : Thursday, February 21, 2008 - 2:58:44 PM
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Christophe Viala. Inversion géoacoustique temps réel de signaux large bande par grands fonds. Mécanique [physics.med-ph]. Université du Sud Toulon Var, 2007. Français. ⟨tel-00258272⟩

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