Independent measurement of extinction and backscatter profiles in cirrus clouds by using a combined Raman elastic-backscatter lidar

TLDR

The Klett method can produce large errors when the lidar ratio varies, whereas simple backscatter lidars still reliably provide cloud optical depth and mean lidar ratio. Extinction and backscatter profiles in cirrus clouds are independently retrieved from elastic and Raman backscatter signals, and the resulting extinction coefficients from both methods are compared using the Klett approach. An extended error analysis shows that lidar ratios in ice clouds typically range from 5 to 15 sr, but can vary strongly between 2 and 20 sr within a single cloud profile, with illustrative examples provided.

Abstract

Height profiles of the extinction and the backscatter coefficients in cirrus clouds are determined independently from elastic- and inelastic- (Raman) backscatter signals. An extended error analysis is given. Examples covering the measured range of extinction-to-backscatter ratios (lidar ratios) in ice clouds are presented. Lidar ratios between 5 and 15 sr are usually found. A strong variation between 2 and 20 sr can be observed within one cloud profile. Particle extinction coefficients determined from inelastic-backscatter signals and from elastic-backscatter signals by using the Klett method are compared. The Klett solution of the extinction profile can be highly erroneous if the lidar ratio varies along the measuring range. On the other hand, simple backscatter lidars can provide reliable information about the cloud optical depth and the mean cloud lidar ratio.