Research On Detection Method And Experiment Of Polarization Lidar For Aerosol Optical Characteristics

Atmospheric aerosol is a complicated multiphase system,which is composed of atmospheric medium and kinds of particles suspending in it.It has very important effects on human health and environment.Depolarization ratio,lidar ratio and Angstrom exponent are important physical parameters of aerosol,which can be detected by polarization lidar,Raman lidar and multi-wavelength lidar respectively.However,current studies show that these three optical variables of aerosol are mostly studied without any connection.Thus the presented research is focused on the studies of depolarization ratio,lidar ratio,Angstrom exponent and their relevance using the polarization lidar.The research result is of great research significance and application value for improving the techniques of the retrieval of aerosol physical properties,revealing the relevance among such three parameters and pushing the development of the comprehensive detection of aerosol physical characteristics with polarization lidar.Based on Mie scattering theory and assumption of particle size distribution,lidar ratio and Angstrom exponent of water cloud,fog and continental aerosols are simulated,aiming to study the relationships among these two parameters and the wavelength of incident light as well as the components of aerosols.The simulation results show that the lidar ratios of water cloud and fog at the wavelengths of 355nm,532nm and 1064nm are all 19sr approximately,and the extinction exponents are almost the same at those wavelengths.The lidar ratios of continental aerosols are found to be positively correlated with the content of soot.The mean value of Angstrom exponent of continental aerosol is 1.3.The simulation results can provide scientific input data for the retrieval of lidar echo signal and the analysis of the optical characteristics of aerosol.In order to improve the performance of the lidar system,a novel method is proposed to calibrate the alignment between the axes of the transmitter and the receiver of the coaxial Mie lidar system,which is based on a criterion of alignment by using the integral of the range corrected signal in certain range.The automatic alignment system is designed using the adjustment algorithm of variable step and the maximization of alignment criterion.The accuracy of the alignment can be up to 0.05mrad.Such design enhances the maneuverability of the lidar system and provides techniques for automation and unattended operation of lidar system.It is found that certain aerosols has the corresponding depolarization ratio,lidar ratio and Angstrom exponent,through analysis of the correlation among these parameters.A retrieval method for fine detection of aerosol using the dual-wavelength micro-pulse polarization lidar system is proposed,which is verified to be effective and reliable.In order to detect the high concentration of aerosols near the ground,a micro-pulse polarization lidar system at eye-safety level is developed,which utilizes the analog detection mode to realize the fine detection of echo signal in a large dynamic range.Continuous observations with scanning in elevation angle are carried out to study the characteristics of aerosol in Xi'an region.The experiment results show that the lidar system can realize the detection of depolarization ratio in the detection range of 80?1000m,which verifies the feasibility of system design and the retrieval algorithm.Such system can be used in the remote sensing of urban aerosol for studying their transportation and spreading.In order to increase the retrieval accuracy of aerosol optical characteristics using Fernald method,a novel method is proposed for the determination of the lidar ratio,which is retrieved by dichotomy.In the process of iterative inversion,the aerosol optical depth in the effective detection range is used as the convergence criterion.Such method for retrieving the lidar ratio of aerosol in lower atmosphere is only using the Mie lidar echo signal and the observation data of sunphotometer,which eliminates the uncertainties caused by the assumption of lidar ratio.In summary,the lidar ratio and Angstrom exponent of kinds of aerosols are analyzed,and micro-pulse polarization lidar with the function of automatic alignment is designed and developed.The detection method and experiment for studying depolarization ratio,lidar ratio and Angstrom coefficients with polarization lidar are studied.The research results realize the fine detection and cross study of aerosol optical characteristics,which is meaningful for revealing the deep regularities of optical characteristics of aerosol.