Chlorophyll-a concentration measure in coastal waters using MERIS and MODIS data

Understanding the temporal dynamic of the biophysical properties of the coastal/shallow waters is a challenging and important task. In the present work Chlorophyll-a concentration in coastal zone shallow waters is obtained by inversion of the MERIS and MODIS level 1 calibrated, geo-located reflectance data. For this purpose, we have used both sensors 1:0 retrieve the chlorophyll concentration, in a scheme of multisensor data assimilation. In fact, the new generation sensor MERIS, on ESA´s ENVISAT, with its spatial resolution of 300 meters and 3 days revisitation time, offers a high number of narrow spectral bands in the visible and in the IR. At the same time, MODIS, on NASA´s Terra and Aqua Satellites, has a lower space resolution but an higher number of bands in the IR portion of the electromagnetic spectrum and can improve our atmospheric correction algorithms. Due to the high variability of the aerosol (type and concentration) and the water type, an accurate atmospheric correction method based on the 6S radiative transfer code has been performed. The atmospheric data required as input to the 6S code have been retrieved from the MODIS data. The estimated chlorophyll-a concentration has been computed from MERIS and MODIS data using a semi-analytic model, based on the optical properties of water and its components. To validate the inversion procedure, ground measurements have been collected monthly during the year 2003 and have been compared with the values derived from the inversion model.