VALIDATING CIRRUS CLOUD OPTICAL PROPERTIES RETRIEVED BY CALIPSO

The spatial and optical characteristics of transparent cirrus clouds measured by CALIPSO are compared to measurements made by the Cloud Physics Lidar (CPL). We examine statistical ensembles of both intrinsic and extrinsic properties, with a particular emphasis on the 532 nm lidar ratio distributions retrieved by the two instruments. Despite differences in the seasonal and geographic data acquisition statistics between the two data sets, the mean values for the two distributions are essentially identical. CALIPSO’s fully automated retrieval scheme yields a lidar ratio of 23 ± 9 sr; the value derived from the CPL measurements is 25 ± 10 sr. Similarly, despite disparities in single shot signalto-noise ratios, the 532 nm optical depth distributions also compare well, with CALIPSO measurements of transparent clouds averaging 0.42 ± 0.37, versus a mean of 0.38 ± 0.29 for CPL.