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

The radiometric sensitivity of the POLarization and Directionality of the Earth’s Reflectances (POLDER) instrument in the ocean color spectral bands (443, 490, and 565 nm) was checked vicariously by comparing top-of-atmosphere normalized radiances measured by the instrument with those computed for the same geometries using a radiative transfer model. In situ measurements of aerosol optical thickness and marine reflectance at the time of the satellite overpass were used as input to the model. The accuracy of the vicarious calibration coefficients was estimated to better than 3%. A large decrease in the POLDER instrument response was found in the blue, confirming the results previously obtained using alternative techniques.