High Precision Inversion Of Aerosol Parameters In Raman-Mie Lidar Combining Space-borne Data

Atmospheric aerosol plays an important role in the physical and chemical processes of the atmosphere and has a significant impact on human health.Lidar is one of the most suitable tools for studying the space-time evolution characteristics of aerosol as a kind of active remote sensing method.This paper outlines the background and significance of lidar detection of the atmospheric aerosol,the research status in China and abroad as well as the large combined observation network of the ground-based lidar and satellite-borne lidar.The structure and parameters of the rotational Raman-Mie Lidar system of the Laser Radar Laboratory at Beijing Institute of Technology are introduced in detail.The data products of CALIOP are introduced briefly.The inversion algorithms apply to the Raman-Mie Lidar and Mie Lidar to calculate aerosol backscatter coefficient and Lidar ratio are discussed.Secondly,the method to determine the geometrical form factor is introduced to solve the problem that ground-based lidar can not fully receive the echoed signal in transition region.A new algorithm is proposed to invert the geometrical form factor by combining the ground-based and space-based synchronous 532nm scattering echoed signal.Besides,the geometrical form factor in coaxial and off-axis modes of the system are inverted by using the experimental data of August 25,2016 and February 27,2017.The off-axis geometrical form factor is almost 0 below 0.6km,so the blind zone of the detection has a large range.The transition zone of the off-axis geometric form factor is 0.6～2.3km and above 2.3km is the full zone.The blind zone range of the coaxial geometrical form factor reduces to 0.18km and the lowest height of the full zone is only 1km which means lidar can receive more echo signal near the ground.The aerosol backscatter coefficients retrieved after calibration are compared with the rotational Raman-Mie geometrical form factor calibration results.The average relative errors are 20.8%and 18.6%respectively which verifies the reliability of the new algorithm.Compared with the results before calibration,the effective inversion heights of aerosol backscatter coefficients are reduced by 1.3km and0.75km respectively.The aerosol backscatter coefficients increased 243.1%and103.95%on average from the lowest detection altitude to the full zone providing the necessary information for judging the atmospheric boundary layer and so on.Finally,the software for the inversion of aerosol optical parameters by rotational Raman-Mie Lidar is introduced.And the data processing is analyzed:denoising,smoothing,geometric form factor calibration and Fernald method,rotational Raman-Mie inversion.The aerosol backscatter coefficients of the Fernald method in three weather conditions are also discussed.The results show that the reference height of the inversion process and the assumption of the lidar ratio have greater impacts on the clean atmospheric backscatter coefficient,the maximum relative errors are respectively 93%and 75%.In addition,the haze observation data recorded in Beijing area from December 30,2016 to January 2,2017 was retrieved.The analysis and discussion between calculated hourly aerosol optical depth（AOD）of 0.3 to 2 km and weather data PM_2.5are made.And the changing characteristics of the haze during the formation and dispersion are given.The results show that the trend of AOD and PM_2.5is consistent.AOD gradually increased from 6:00 in the evening and reached a steady state in the early morning under the condition that meteorological conditions not conducive to aerosol diffusion,and reached a maximum of 0.552 at 22:00 on the 31st.During the process of haze dissipation,PM2.5 descended at a faster rate than AOD at the same time,which indicated that the near-surface aerosol diffused more rapidly.