Fusion of MeRIS and ETM images for coastal water monitoring

Ocean colour monitoring is usually based on optical remote sensing with spatial resolutions around 1 km. This spatial scale is available with such sensors as NOAA-AVHRR, POLDER or SeaWiFS, which cover one to several thousand kilometers in a single swath and providing very short revisit periods. The MeRIS sensor, launched on board ENVISAT in 2002, was designed for sea colour observation, with a 300 meter spatial resolution, 15 programmable spectral bands and a 3 day revisit period. Tree hundred meter is a high resolution for an oceanographic sensors, but it is still too rough for coastal water monitoring, where physical and biological phenomena require better spatial resolution [1]. On the opposite, multispectral Landsat ETM images offer a suitable spatial resolution, but have only 4 spectral bands in the visible and near infrared spectrum, allowing poor spectral characterization. A few years ago, in order to combine the spectral resolution of MeRIS and the spatial resolution of Landsat ETM, we had implemented a merging method proposed by Zhukov et al. [2]. Before the launch of ENVISAT, we applied this method to simulated MeRIS images [3]. MeRIS was launched in March 2002 and has been providing images since June 2002. This method is now applied to real MeRIS images. Two product levels are considered. Level 1b contains radiance measurements at the top of the atmosphere for the calibrated and geocoded fifteen (15) MeRIS bands. Level 2 contains normalized surface reflectance and several geophysical and biophysical parameters such as algal pigment index, suspended sediment, Rayleigh-corrected Vegetation Indices, aerosol type, cloud albedo. The method was tested for radiance (level 1b) and reflectance (level 2) over a coastal area of approximately 30×30 km2 located around the Thau lagoon (southern France).