Backscatter Color Ratios of Cirrus Clouds Measured by the Cloud Physics Lidar

The Cloud Physics Lidar (CPL) is a threewavelength, polarization-sensitive elastic backscatter lidar that flies aboard NASA’s high-altitude ER2 research aircraft. This work presents spatial and optical analyses of the combined cirrus cloud measurements acquired by CPL during eight separate field campaigns occurring from 2002 to 2007. Particular attention is given to the retrieval and characterization of the backscatter color ratio, defined as the ratio of the particulate backscatter coefficients measured at 1064 nm and 532 nm. Recent space-based lidar missions rely on assumptions about the backscatter color ratio to calibrate their 1064 nm measurements. Because the signal-to-noise ratio of the CPL data is substantially higher than that of spacebased systems, CPL can calibrate its 1064 nm channel using the well-established molecular normalization technique. Analysis of the CPL data sets can therefore provide the independent evaluation of cirrus cloud backscatter color ratios that is required to validate fundamental components of the calibration schemes employed by space-based lidars.