MERIS potential for ocean colour studies in the open ocean

The interest of space observations of ocean colour for determining variatio ns in phytoplankton distribution and for deriving primary production (via m odels) has been largely demonstrated by the Coastal Zone Color Scanner (CZC S) which operated from 1978 to 1986. The capabilities of this pioneer senso r, however, were limited both in spectral resolution and radiometric accura cy. The next generation of ocean colour sensors will benefit from major imp rovements. The Medium Resolution Imaging Spectrometer (MERIS), planned by t he European Space Agency (ESA) for the Envisat platform, has been designed to measure radiances in 15 visible and infrared channels. Three infrared ch annels will allow aerosol characterization, and therefore accurate atmosphe ric corrections, to be performed for each pixel. For the retrieval of marin e parameters, nine channels between 410 and 705 nm will be available (as op posed to only four with the CZCS). In coastal waters this should, in princi ple, allow a separate quantification of different substances (phytoplankton , mineral particles, yellow substance) to be performed. In open ocean water s optically dominated by phytoplankton and their associate detrital matter, the basic information (i.e. the concentration of phytoplanktonic pigments) will be retrieved with improved accuracy due to the increased radiometric performances of MERIS. The adoption of multi-wavelength algorithms could al so lead to additional information concerning auxiliary pigments and taxonom ic groups. Finally, MERIS will be one of the first sensors to allow measure ments of Sun-induced chlorophyll alpha in vivo fluorescence, which could pr ovide a complementary approach for the assessment of phytoplankton abundanc e. The development of these next-generation algorithms, however, requires a number of fundamental studies.