Research Of Water Cloud Parameters Combined With Multi-scattering Polarization Lidar

Multi-scattering occurs when a laser transmits into dense atmosphere targets(e.g.fogs,smoke or clouds),which can cause depolarization effects even though the scattering particles are spherical.In addition,multi-scattering effects have additional information about microphysical properties of scatters.Thus,multi-scattering can be utilized to study the microphysical properties of the liquid water cloud.In this paper,a Monte Carlo method was used to simulate multi-scattering transmission properties of Lidar signals in the cloud.The results show that the slope of the degree of linear polarization(SLDLP)is only related to the extinction coefficient of clouds,and the saturation of the degree of linear polarization(SADLP)will change with the cloud effective size(CES)and the field of view(FOV),which means that the extinction coefficient of cloud can be obtained by calculating the SLDLP.The CES and liquid water content(LWC)can be inversely performed by using the SADLP and the extinction coefficient.Based on the calculation results,a new method was proposed to inverse the microphysical properties of liquid water clouds by using multi-scattering effects.On the basis of theoretical analysis,a set of multi-scattering polarization Lidar(MSPL)system was designed and built,and the calibration of the system is completed through experiments.By analyzing the typical observation data of MSPL in the northern suburbs of Nanjing,China,the LWC and CES of the liquid water cloud were obtained.Comparisons between the results from the MSPL,MODIS and the Microwave radar data showed that,the microphysical properties of liquid cloud could be retrieved by combining our MSPL and the inversion method.The profiles of atmospheric extinction coefficient at different FOVs were also analyzed by using the data of MSPL,and then the extinction coefficient and optical depth of cloud before and after the correction of multiple scattering factors are compared.It is found that the multi-scattering will reduce the extinction coefficient and optical depth of cloud.