Lidar and Radioinetric Observations of Cirrus Clouds

Abstract

The technique of using combined lidar (0.694µm) and radiometric (10–12µm) measurements on cirrus clouds was developed in order to determine their infrared emissivity and to examine the experimental relationships between the infrared and lidar data. Detailed measurements of cirrus infrared emissivity and lidar backscatter were made on several cirrus systems at Adelaide in November 1970. The mean zenith emissivity of cirrus was found to be 0.245. Emissivity was only weakly correlated with thickness. The cirrus extinction coefficient, which is proportional to the particle density, was totally uncorrelated with mid-cloud temperature. Various infrared and visible optical quantities were calculated from the experimental data and the relationships between some of these quantities were examined. The lidar backscatter amplitude integrated through the cloud was found to be well correlated with the infrared optical thickness. A simple model of absorption and scattering of radiation in a cloud of large (σ50µ... Abstract The technique of using combined lidar (0.694µm) and radiometric (10–12µm) measurements on cirrus clouds was developed in order to determine their infrared emissivity and to examine the experimental relationships between the infrared and lidar data. Detailed measurements of cirrus infrared emissivity and lidar backscatter were made on several cirrus systems at Adelaide in November 1970. The mean zenith emissivity of cirrus was found to be 0.245. Emissivity was only weakly correlated with thickness. The cirrus extinction coefficient, which is proportional to the particle density, was totally uncorrelated with mid-cloud temperature. Various infrared and visible optical quantities were calculated from the experimental data and the relationships between some of these quantities were examined. The lidar backscatter amplitude integrated through the cloud was found to be well correlated with the infrared optical thickness. A simple model of absorption and scattering of radiation in a cloud of large (σ50µ...