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Amélioration des méthodes de détection et de qualification des sondes pour les sondeurs multifaisceaux bathymétriques

Abstract : Multibeam echosounders (MBES) are complex sonar systems giving accurate bathymetric measurements over a wide angular sector by forming several hundreds of steered beams. This work deals with the topics of measurement qualification and the study of the possibility to take several soundings into account inside each formed beam. The definition of the quality is based on the classical estimation methods used in MBES to determine the water depth and on their variance derivation. This requires a good knowledge of the statistical properties of the acoustic signals according to the measurement conditions and the sounder settings, in order to derive the theoretical variance of the time of arrival inside each beam. Those developments define a quality estimator for each computed sounding in each beam, depending only on the acoustical signal properties. They were conducted specifically for the measurement of the time of arrival from the envelope of the amplitude signal, taking into account the impact of additive noise and the pulse length. The validation of the theoretical formulas on real data shows the relevance of the results. The study of the implementation of multidetection algorithms begins by underlining the loss of information caused by the selection of only one sounding per beam, and by observing the intrinsic measurement limitations caused by MBES antennas typical configuration. Several processing methods designed to implement a multidetection algorithm are then defined. These processes are based on the characterization of the nature of underwater target (isolated, one-dimensional, extended) and of their spectral properties. For those, a criterion relying on the "effective bandwidth" of the received signal makes it possible to distinguish real targets from noise. This finally resulted into the implementation of a multidetection algorithm which was be tested on several datasets acquired in complex underwater environments. The results obtained on real data show the interest residing in taking into account several soundings per beam. The results of this work contribute to the hydrographic performance improvement of MBES, giving a quality estimation of the acoustical measurement in real-time for each sounding and a better description of complex underwater targets.
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  • HAL Id : tel-00783671, version 1

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Yoann Ladroit. Amélioration des méthodes de détection et de qualification des sondes pour les sondeurs multifaisceaux bathymétriques. Traitement du signal et de l'image [eess.SP]. Télécom Bretagne, Université de Rennes 1, 2012. Français. ⟨tel-00783671⟩

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