Airplane based measurements of solar spectral radiances reflected by cirrus are collected with the High Altitude and Long Range Research aircraft HALO in November 2010. The data are used to quantify the influence of surface albedo inhomogeneities on the retrieval of cirrus optical thickness and crystal effective radius. Based on radiative transfer calculations the cirrus properties are derived using a standard retrieval method. Frequency distributions of the surface albedos derived from satellite observations are used to create retrieval tables for the cirrus optical thickness and effective. Then a statistical retrieval approach is applied to investigate the influence of surface albedo inhomogeneities. Retrieval results for the cirrus optical thickness are compared to Lidar derived values. Furthermore the role of ice crystal shape in this regard is investigated.

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