Remote sensing of the southern ocean by MERIS, MODIS, SeaWiFS and ENEA Lidar

Oceanic phytoplankton plays a major role in climate regulation. This explains the international efforts in space monitoring of chlorophyll-a concentration, i.e. the main indicator of algal biomass. In this study three radiometers (MERIS, MODIS and SeaWiFS), aboard satellites, and the ENEA lidar, aboard a ship, are intercompared. Important discrepancies among the radiometers have been observed. In particular, MERIS can be up to 100% apart from MODIS and SeaWiFS. This difference reduces to about 35% if MERIS is calibrated with the ENEA lidar. Those results confirm the unavoidable need of precise measurements of chlorophyll-a concentration in close proximity to the sea surface. Moreover, it is demonstrated that regional calibrations of satellite radiometers lead to more accurate estimates of oceanic phytoplankton.