Airborne CASI imagery for bathymetric study in Reunion Island (Indian Ocean)

The following submission paper has been prepared to describe the various components of the Reunion island remote sensing project. This project was undertaken by the "Centre de Cooperation Internationale en Recherche Agronomique pour le Developpement" (CIRAD) to conduct airborne CASI data collection surveys in Reunion Island. The data resulting of this campaign will serve several projects as SUCRETTE (System de sUivi de la Canne a suCRe par TeledeTEction) or AGIL (Aide a la Gestion Integree des Littoraux). These projects are focused on the use of remote sensing data in the environmental monitoring studies. They will bring support to the field actors on the aspect of pollution (urban extension pressure, agricultural areas above coral reefs) by coastal reef monitoring, or farming method (fertilizer, harvest monitoring) by analyzing indicators (plant stress...). One aspect of the use of the collected data is presented here. The purpose of this study is to analyze the possibility of superspectral imagery on coral reef in tropical environment. The data collection phase of the project took place between Sept 15th and Oct 4th, 2002 in Reunion Island. Several lines were taken (41 transects at 2 m spatial resolution over 19 bands) over coral reef on the south-west coastal part of the island. The CASI system was provided by a Canadian company HDI (Hyperspectral Data Incorporated). A previous CASI campaign had occurred on the same places in 1996 and will allow us to analyze the evolution of the benthos fauna (algae and coral). However, on a first step, a study of bathymetry was done and is presented here. Several wavelength in the visible and infrared part of the spectrum were used with the methodology developed by W. D. Philpot and used by S. Andrefouet. Referenced points (geographic position, depth and spectral reflectance on white submerged targets) were acquired on the field during the acquisition CASI data campaign. A procedure of treatment developed on IDL language has been used to obtain an accurate map of bathymetry that the accuracy was checked with depth points already taken on the field with DGPS.