Topographic indices of the seabed of the reef areas of the Eparses Islands — Project Piot and IoT

Topographic indices related to the reliefs of the background were extracted from the Lidar Litto 3D bathymetry of the islands of Europa (project Piot), Tromelin, Bassas de India, Glorieuses and Juan de Nova (IoT project) The product of the 3 topographic indices IPM (Roughness Index), IPV (Lange Variance Index) and ICM (Convisability Index) for the calculation of the TTI (Topographic Turtles Index), allows to retain only areas where all values are strong, masking areas where at least one of the factors approach zero. The three parameters (slope, slope variance, and concavity) must be close to their optimum in order for the conditions to be considered favourable to the presence of turtles. This hypothesis was based on the analysis of the data on La Réunion (CHARC program) and may or may not be confirmed later in the analysis of turtle location data. The MNT Lidar produced under Litto3D® was acquired in 2009-2010. The Piot project is co-financed by the Iles Éparses Consortium2017-2020, Ifremer (carrier) and its partners (CNRS-LIRMM, Kelonia and CEDTM). The IoT project is co-financed by the ERDF-INTERREG V OI, the State, Ifremer (carrier) and its partners (CNRS-LIRMM, French Southern Lands and Antartiques, Departmental Council of Mayotte, Marin Natural Park of Mayotte, Oulanga Na Nyamba Association of Mayotte and Seychelles Islands Foundation).