Integration of shipborne lidar and spaceborne radiometer: application to the Antarctic coastal environment

Abstract

Since 1997, the ENEA Lidar Fluorosensor (ELF) carries out measurements of phytoplanktonic pigments, in vivo phytoplankton fluorescence yield, chromophoric dissolved organic matter (CDOM) and photosynthetically active radiation (PAR) in the coastal zone of Antarctica, one of the more interesting but less investigated environment of our planet. With respect to ocean color satellite radiometers, ELF is insensitive to clouds, free from atmospheric correction and accurate also in case II waters. Nevertheless, in order to take advantage of both the synoptic view of the satellite radiometers and the sea truth of the lidar fluorosensors, ELF measurements have been used to calibrate a chlorophyll-a (Chl-a) bio-optical algorithm and to develop a CDOM bio-optical algorithm, both based on the radiometer-derived water leaving radiance, and to elaborate a new Chl-a bio-optical algorithm based on the radiometer-derived sun-induced Chl-a fluorescence. In fact, ELF data are more suitable to that purpose than usual in situ sampling because their geographic coverage and spatio-temporal resolution are closer to image extent and pixel size/time, respectively, of the satellite products. ELF-calibrated Chl-a and ELF PAR have then been used as input variables for a vertically generalized production model tuned in Antarctic waters. As a consequence, a new primary production regional model for the Southern Ocean is available. Those results, from one hand, help in understanding extensions and dynamics of coastal processes, like phytoplankton blooms, from the other hand, indicate that standard algorithms can misestimate the algal biomass.