COMBINATION OF LIDAR, MODIS AND SEAWIFS SENSORS FOR SIMULTANEOUS CHLOROPHYLL MONITORING

Ocean colour satellites have changed our way to observe the Earth: Planetary maps of the surface chlorophyll-a concentration, and hence of the phytoplankton primary productivity, can be retrieved in few days. Nevertheless, these results are the product of complex calculations: Atmospheric cor- rections and bio-optical algorithms have to be applied on the raw water-leaving radiances meas- ured by the spaceborne radiometers. For this reason, the remote sensed images have to be cali- brated and validated by in situ instruments, usually operated from marine buoys, fixed stations, and research vessels (RVs). The ENEA lidar fluorosensor (ELF), aboard the RV Italica, is one of the shipboard lidar devoted to oceanographic studies. It measured continuously surface chlorophyll-a concentrations during the Italy - New Zealand and New Zealand - Italy transects (13 November - 18 December 2001 and 28 February - 1 April 2002, respectively). This study is part of the MIPOT (Mediterranean Sea, Indian and Pacific Oceans Transect) oceanographic campaign and provided the "sea truth" in less studied marine zones (Red Sea and Indian Ocean). As in previous lidar-satellite comparisons, the ELF measurements were compared to the imagery collected by SeaWiFS and MODIS. This study pointed out advantages, disadvantages, and possi- ble synergies of lidar fluorosensor and spaceborne radiometers. In particular, the SeaWiFS and MODIS bio-optical algorithms have been calibrated with the ELF data. The differences between the performances of the two satellite sensors are also briefly discussed.