Operational ocean color approach with Vegetation /SPOT-4

Demand for near-real-time satellite ocean observations is rapidly increasing with the development of operational oceanography and its applications such as ocean monitoring for offshore oil exploitation, fish resources management or detection of surface pollution. Ocean color is one of the few important ocean properties measurable from space. Vegetation, launched on-board SPOT-4 in 1998, is a push- broom sensor equipped with 4 wide field-of-view cameras corresponding to 4 spectral bands: blue, red, near-IR and SWIR bands. Unlike SeaWiFS or MODIS, vegetation was not designed for ocean color studies. Nevertheless, we demonstrate here that useful ocean color measurements can be deduced from the vegetation blue band, the only that is significantly sensitive to the marine reflectance. The main processing steps include: i/correction for gaseous absorption, ii/correction for molecular scattering which represent, for the blue band up to 90 percent of the total observed radiance, and iii/correction for aerosol scattering. Vegetation system being fully operational, near- real-time ocean color observations can thus be obtained with this instrument. The first results, concerning a limited ocean region, are presented and compared with SeaWiFS and radar altimeter observations.