Projet Life Intégré Marha. Potentiel du capteur hyperspectral sous-marin (UHI) pour la cartographie et l’évaluation de l’état des habitats benthiques côtiers et profonds. Bilan d’activités de l’Ifremer pour le volet technologie.

This document constitutes the final report of the LIFE Marha project, presenting the work carried out by Ifremer under the Technology task. Hyperspectral imaging, widely used in coastal zones, was adapted to deep-sea environments through the integration of an underwater sensor (UHI, 378–800 nm) on Ifremer’s HROVs, within the framework of the Marha and iAtlantic projects. A processing chain combining radiometric corrections (Lee model) and geometric corrections (3D reconstruction linking UHI, HD camera, and SLAM) produces precise hyperspectral orthomosaics suitable for detailed analyses. Tests conducted at Catchoff (90–100 m) and in the Lampaul canyon (750 m) demonstrated effective discrimination of species and substrates. Among the algorithms tested, Random Forest achieved an overall accuracy of 0.98 and revealed, at Lampaul, a very low proportion of live coral (≈ 2 %) and high fragmentation, indicating significant site degradation. These results confirm the potential of underwater hyperspectral technology for mapping and monitoring deep ecosystems. Further efforts are needed to enable high-frequency operational deployment.