Derivation of SeaWiFS vicarious calibration coefficients using in situ measurements in Case 2 water of the Baltic Sea

In this paper, the vicarious calibration technique is used to improve the performance of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) onboard the OrbView-2 spacecraft to get reliable results for the concentration of water constituents in turbid waters of the Baltic Sea. The technique is used to determine mean vicarious calibration coefficients that are multiplied with the slope of SeaWiFS calibration equation and consequently enhance the preflight calibration coefficients. The standard SeaWiFS test site for the derivation of such coefficients is situated in a clear water region where the optical properties of the water are determined by the phytoplankton and its degradation products. In this paper, mean vicarious calibration coefficients are derived for the first time from in situ measurements in Case 2 water of the Baltic Sea. It was found a necessary adjustment of +3% for the center wavelength of 412 nm and between −0.1% and −3% for 443–670 nm. Similar coefficients were found by other research groups. The result is a maximum deviation of 33% in the channels 490–670 nm of determined SeaWiFS normalised water-leaving radiances considering the derived vicarious correction coefficients from the in situ radiances. The deviation is greater at the channels 412 and 443 nm due to higher inaccuracy of atmospheric correction in the blue spectral range.