Cloud optical parameters from airborne observation of diffuse solar radiation accomplished in USA and USSR in different geographical regions

Abstract

Cloud optical parameters (optical thickness, single scattering albedo, and ground albedo) are obtained from airborne experiments with NASA’s Cloud Absorption Radiometer and analysed taking into account observational and processing uncertainties. The analytical approach of the inverse asymptotic formulas of the transfer theory, which uses observed values of solar diffuse radiance, is applied. The method is free from a priori restrictions and links put to desired parameters. The algorithms and first results of processing have been presented earlier. The first results, being the solution of the inverse problem, showed strong fluctuations in values, which required the regularization of the solution. The dependence of uncertainties of the result on viewing direction was revealed. Hence, here attention is focused on uncertainties of observation, angle function calculation, and processing approach, which is taken into account for result averaging, and the regularization procedure is described. Calculating the uncertainties of the processing approach is accomplished analytically using formulas for the retrieval of the optical parameters. The values of the desired parameters obtained in eight observational spectral channels – above, below, and within the cloud – at 16 levels are presented. The final results are compared to the optical parameters of extended cloud layers obtained earlier using a similar method of inverse asymptotic formulas from spectral data of Russian aircraft solar irradiance measurements in different regions, made in the 1970s/1980s at Leningrad (now Saint Petersburg) University in the USSR.