Vicarious calibration of the POLDER ocean color spectral bands using in situ measurements

The radiometric sensitivity of the POLarization and Directionality of the E arth's Reflectances (POLDER) instrument in the ocean color spectral bands ( 443, 490, and 565 nm) was checked vicariously by comparing top-of-atmospher e normalized radiances measured by the instrument with those computed for t he same geometries using a radiative transfer model. In situ measurements o f aerosol optical thickness and marine reflectance at the time of the satel lite overpass were used as input to the model. The accuracy of the vicariou s calibration coefficients was estimated to better than 3%, A large decreas e in the POLDER instrument response was found in the blue, confirming the r esults previously obtained using alternative techniques.