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Hyperspectral Remote Sensing Of Wild Oyster Reefs
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International audience. The invasion of the wild oyster Crassostrea gigas along the western European Atlantic coast hasgenerated changes in the structure and functioning of intertidal ecosystems. Considered as an invasivespecies and a trophic competitor of the cultivated conspecific oyster, it is now seen as a resource byoyster farmers following recurrent mass summer mortalities of oyster spat since 2008. Spatialdistribution maps of wild oyster reefs are required by local authorities to help define managementstrategies. In this work, visible-near infrared (VNIR) hyperspectral and multispectral remote sensingwas investigated to map two contrasted intertidal reef structures: clusters of vertical oysters buildingthree-dimensional dense reefs in muddy areas and oysters growing horizontally creating large flat reefsin rocky areas. A spectral library, collected in situ for various conditions with an ASDspectroradiometer, was used to run Spectral Angle Mapper classifications on airborne data obtainedwith an HySpex sensor (160 spectral bands) and SPOT satellite HRG multispectral data (3 spectralbands). With HySpex spectral/spatial resolution, horizontal oysters in the rocky area were correctlyclassified but the detection was less efficient for vertical oysters in muddy areas. Poor results wereobtained with the multispectral image and from spatially or spectrally degraded HySpex data, it wasclear that the spectral resolution was more important than the spatial resolution. In fact, there was asystematic mud deposition on shells of vertical oyster reefs explaining the misclassification of 30% ofpixels recognized as mud or microphytobenthos. Spatial distribution maps of oyster reefs werecoupled with in situ biomass measurements to illustrate the interest of a remote sensing product toprovide stock estimations of wild oyster reefs to be exploited by oyster producers. This workhighlights the interest of developing remote sensing techniques for aquaculture applications in coastalareas.
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