A New Analytical Procedure to Derive the Scattering Parameter of Optically Thin Clouds from Lidar Data

We propose a new analytical procedure to derive the scattering parameter S (=extinction/backscattering ratio) of the optically thin cloud using the difference in the attenuation of two returned signals measured by a lidar. In the procedure, there is a assumption that the aerosol layers below the cloud layer do not change during the observation, and a value of backscattering coefficient at a height above the cloud layer is necessary. The former assumption is different from that of the Fernald's method in which the scattering parameter is assumed to be a constant value in itself in order to derive the extinction coefficient profile. The sensitivity test for the procedure shows that the errors in S increase in accordance with the decrease in the value of S. It also shows that if the absolute values of the difference in the scattering ratio of the cloud used for the derivation of S are equal, the errors in S are very similar to each other no matter how the optical thickness of the cloud is. The error increases in accordance with the decrease in the difference in the scattering ratio.