Retrieval of cloud parameters from the multiple scattered lidarsignals

摘要

The conventional lidar technique is elaborated to measurenparameteres of the atmospheric aerosols where the single scatteringnapproximation is valid. This technique fails to measure the sizendistribution and the number density profile of the cloud particlesnbecause of the great optical density of clouds where the process ofnmultiple scattering of the lidar signal becomes predominant. The processnof multiple scattering essentially smoothes out the information on thencloud parameters and the inverse problem looks rather hopeless. Theninformation on the cloud parameters is not lost so quickly in thenmultiple scattering process due to the small angular scattering when thenparticles sizes are greater than the lidar wavelength. In this case, theninverse problem can be successfully considered and applied for thenmoderate optical depths. To use the advantage of the small-angularnscattering, in this paper the multiple scattered radiation is dividedninto two parts: the small-angular or multiple diffracted part and thenresidue or the quasi-isotropical part. The division procedure is strictnand the proper radiative transfer equations for the both terms arenwritten down. The equation for MDP is solved analytically using thenknown small-angular approximation of the radiative transfer equation.nThe simple analytical expression obtained for the small-angularndistribution of the lidar signals is used to construct an analyticalnalgorithm to retrieve the particle size distribution or the numberndensity profile of those cloud particles which are greater than thenwavelength. The obtained lidar algorithm can be the basis of thenquantitative theory. To extract the multiple diffracted part from thenwhole experimentally measured lidar signal, the numerical calculationsnof the lidar signal based on the Monte-Carlo method have been made