MERIS forms part of the core instrument payload of ESA's environmental research satellite ENVISAT-1. The demands of the European scientific community for a global environmental monitoring system, whose technical characteristics enable the extraction of quantitative information from ocean color data, as well as for documentation of the state and evolution of the atmosphere and land surfaces, led to the conception of MERIS. The oceanographic mission is radiometrically the most demanding in terms of low radiance levels and their associated high signal-to noise ratios. Therefore, the instrument must be capable of detecting the low levels of radiation emerging from the ocean (linked to the water constituents by the processes of absorption and scattering). The characteristics of MERIS are also of great value for the retrieval of information on land surfaces, in particular that of global biomass.