Combined retrieval of Arctic liquid water cloud and surface snow properties using airborne spectral solar remote sensing

摘要

The passive solar remote sensing of cloud properties over highly reflecting ground is challenging, mostly due to the low contrast between the cloud reflectivity and that of the underlying surfaces (sea ice and snow). Uncertainties in the retrieved cloud optical thickness tau and cloud droplet effective radius r(eff);(C) may arise from uncertainties in the assumed spectral surface albedo, which is mainly determined by the generally unknown effective snow grain size r(eff;S). Therefore, in a first step the effects of the assumed snow grain size are systematically quantified for the conventional bispectral retrieval technique of tau and r(eff;C) for liquid water clouds. In general, the impact of uncertainties of r(eff;S) is largest for small snow grain sizes. While the uncertainties of retrieved tau are independent of the cloud optical thickness and solar zenith angle, the bias of retrieved r(eff;C) increases for optically thin clouds and high Sun. The largest deviations between the retrieved and true original values are found with 83% for tau and 62% for r(eff;C).