ICE-CLOUD DEPOLARIZATION OF BACKSCATTER FOR CO2 AND OTHER INFRARED LIDARS

The depolarization of backscatter from ice particles at the CO2 lidar wavelength of 10.59 mum was investigated through field measurements, with simultanous depolarization measurements taken at 0.6943 mum for comparison. The depolarization ratio at the infrared wavelength was usually at or below the lidar's sensitivity limit of 0.01, which is dramatically smaller than the typical 0.5 linear depolarization ratio for short-wave lidars. This behavior is explained by the strong absorption of ice at the infrared wavelength. Depolarization measurements at a 10.59-mum wavelength cannot discriminate between ice and water clouds in the manner of short-wave lidars. A possibility exists for more prominent depolarization at shorter CO2 lidar wavelengths (e.g., 9.115 mum), but additional research is required. Depolarization at the 2.09-mum wavelength is predicted to be substantial and useful for hydrometeor observations.