Accuracy Of Radiometric Calibration Of Ocean Color Satellite Sensors Using AERONET-OC Data

Ocean Color (OC) satellite sensors require accurate radiometric calibration in order to provide reliable estimates of concentrations of water constituents. In addition to the pre-launch, instrument-level calibration, system vicarious calibration is applied after launch in which wavelength-dependent correction factors (gains) are obtained by forcing satellite-derived water-leaving radiances to agree with in-situ measurements. Alternatively, data from ancillary instrumentation, acquired simultaneously to the satellite overpass, can be used to characterize the model atmosphere/ocean system in radiative transfer (RT) codes capable of reproducing the top-of-the-atmosphere (TOA) radiances. The main advantage of this approach is its independence of any atmospheric correction procedure. A portion of the AErosol Robotic NETwork sunphotomoters (AERONET-OC) have been upgraded over the years to provide water leaving radiance measurements in addition to aerosol products. These upwelling radiances can be used to infer inherent optical properties of the water constituents through available algorithms. AERONET-OC observations provide therefore appropriate input to characterize the atmospheric and oceanic layers in RT simulations. We exploit these AERONET-OC datasets and investigate the performance of accurate RT codes in modeling the conditions at six different stations in US and Europe. The gains are determined from statistically significant amount of filtered pixels covering three years of operations for the MODIS, VIIRS and partially MERIS sensors. The analysis enables the determination of the sensitivity of the TOA radiances to the uncertainties in individual model parameters, thereby quantifying the accuracy of the calibration approach.