No map of the sea floor is available yet on the whole lagoon of New Caledonia. We tried to validate a method to map it with MeRIS images on the south western part of the lagoon. The non-linear effect of water column light attenuation can then be corrected to obtain the absolute reflectance of the seabed. Light attenuation by the water column can be determined by comparing the radiance of standard features on the seabed at different depth. Bathymetry can also be determined by measuring the relative reflectance of the seabed in green and red light spectral bands. Once the effect of attenuation has been removed, a supervised classification can be applied in order to obtain the location of each item on the sea floor. Validations are operated with ground measurements of depth, spectral profiles and some available maps.

Bathymetric estimation can be obtained from multispectral satellite images for shallow waters. The method is based on the rotation of a pair of spectral bands. One of the resulting images is depth-dependent. Therefore several pixels corresponding to different depths are required to numerically evaluate the linear relation between the pixel values and the real depth for a training area. The aim of this study is to compare, for one bathymetric estimation method and one mesotrophic site, the results of depth estimation with a large panel of satellite and aerial images: CASI, QUICKBIRD, CHRIS PROBA, ETM, HYPERION and MeRIS. For each image the pair of spectral bands chosen to compute the bathymetry has been optimized. Error on depth estimation has been computed on two regions of the image: the training area and a validation area. This comparison is discussed to identify the influence of image parameters (spectral bands, S/N ratio, spatial resolution, and quantization) on the bathymetric results and to propose the most adapted image parameters for bathymetric estimation. For validation purposes, we compared the results obtained with a CASI image matching the optimized parameters in an oligotrophic site in the Red Sea.

The Medium Resolution Imaging Spectrometer (MERIS) launched in March 2002 and has been providing images since June 2002. Before its launch, we had implemented a method to improve its resolution by merging its images with Landsat Enhanced Thematic Mapper images in order to preserve the best characteristics of the two images (spatial, spectral, temporal). We now present the results of this method for real MERIS images (level 1b and 2) in a coastal area. The robustness of the method is studied as well as the influence of the delay between the acquisitions of the two images.

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.

The aim of our study is to develop products and services for coastal zone management based on the exploitation of hyperspectral sensors as CASI, MeRIS or Hyperion. Bathymetry, seabed features map and water quality products are hardly required for a more effective monitoring and management of such sensitive and dynamic areas. Data correction from atmosphere, sunglint and attenuation effects are presented as well as products previously cited. These products provided by different sensors will be integrated in a prototype tool dedicated to coastal decision-makers. Our user-oriented approach should provide valid and systematic information on seashore to complete in situ measurements. This approach will takes advantage of the temporal, swath and spectral resolution of MERIS sensor and the spectral and spatial resolution of Hyperion or CASI. Fusion tool will be integrated in the prototype in order to improve MeRIS resolution and to keep its swath and its temporal repetitivity.

The medium resolution imaging spectrometer (MeRIS) is ready to be launched. Considering its spatial resolution (240 m), potential users will have to face the mixed pixel problem. The authors propose to improve its resolution by merging MeRIS images with Landsat TM images. The best characteristics of the two images (spatial, spectral, temporal) are then preserved.