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Mesure de Matières En Suspension (MES) dans la colonne d'eau par combinaison de méthodes acoustiques et optiques

Abstract : Measuring Suspended Particulate Matter (SPM) is essential to better understand sediment transport and marine ecosystems. SPM is traditionnaly estimated through in situ water samples analysis, or based on the optical properties of water. Yet for several decades, acoustical devices have shown their capability to measure SPM on larger volumes. These measurements (especially in terms of SPM concentration) are based on the backscattering properties of the particles. However, these measurements remain limited, since the SPM content in the water column is subjected to variations on both spatial and temporal scales.As a first step, this work aims at showing that it is possible to increase the degree of spatialization of the SPM measurements by inverting MultiBeam EchoSounder (MBES) data, through in situ measurements acquired in the Aulne macrotidal estuary. A backscattering model was first designed to describe the backscattering properties of the suspension of interest, consisting in this study in estuarine agregates. Then, thanks to multifrequency observations, the SPM mass concentration sorted by size classes was retrieved through the the resolution of the inverse problem. This kind of information allows to determine the equivalent spherical radius of the the whole suspension, through which the MBES data, calibrated beforehand using an original method, can be directly inverted. Subsequently, a study of the uncertainties attached to the final concentration estimate is proposed in order to qualify the relevance of the results.In a second step, the necessary conditions for establishing a measurement protocol of the SPM are identified. The latter allows continuous characterization of SPM at different spatial and temporal scales, by exploiting the complementarity of the measures delivered by different instruments.
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https://tel.archives-ouvertes.fr/tel-01560956
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Submitted on : Tuesday, December 18, 2018 - 3:37:15 PM
Last modification on : Wednesday, October 14, 2020 - 3:52:11 AM
Long-term archiving on: : Wednesday, March 20, 2019 - 11:52:27 AM

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Guillaume Fromant. Mesure de Matières En Suspension (MES) dans la colonne d'eau par combinaison de méthodes acoustiques et optiques. Océanographie. Université de Bretagne occidentale - Brest, 2015. Français. ⟨NNT : 2015BRES0058⟩. ⟨tel-01560956v2⟩

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