Calculation Of Atmospheric Aerosol Optical Depth Based On Micro-pulse Lidar

Aerosol optical depth is an important optical parameter to describe the extinction characteristics of aerosol,and it is the vital key factor in the study of radiative effects of climatology.It has vital scientific significance and application value in the field of climatology,atmospheric optical transmission,remote sensing application and environment monitoring.At present,the main methods of remote sensing aerosol optical thickness include space-based remote sensing and ground-based remote sensing.The space-based remote sensing mainly refers to the satellite remote sensing,which can detect the large area.The main applications of remote sensing in ground-based remote sensing are sun-photometer and lidar.Sun-photometer has the highest accuracy,but it can only accurately obtain the whole layer of atmospheric aerosol optical depth in the sunny and cloudless daytime.Lidar is an active remote sensing method,which can make up for the deficiency of the sun-photometer.The conventional method using lidar to retrieve the aerosol optical depth is directly to integral of the aerosol extinction coefficient of finite height.However,the detection height of lidar is limited,and this method do not get the whole layer of aerosol optical depth.This paper presents a method for calculating the aerosol optical depth by scaling height.Aerosol scaling height is an important parameter to reflect the aerosol vertical distribution.The method of calculating aerosol scaling height is usually measured by sun photometer and the visibility meter.The sun photometer only get the accurate aerosol optical depth in the cloudless daytime period,so the aerosol scaling height of the corresponding period can only be obtained by the conventional method.This paper inverse aerosol scaling height based on Micro Pulse Lidar,then combining with surface extinction coefficient to calculate the atmospheric AOD.Finally,the main works are as follows:1.Inverse aerosol scaling height based on micro-pulsed lidarFirst,the vertical extinction profile of aerosol is obtained by Fernald method,after statistical analysis,four typical profile types are given;Then the corresponding calculation methods of aerosol scaling height are given according to the characteristics of four profiles,and the trend of aerosol scaling heights were obtained.The results show that the values of the scaling height are smaller in the night and the morning,however,the values are larger in the daytime and the maximum was reached in the afternoon.In the end,the correlation between the scaling heights obtained by lidar and the conventional method is analyzed.It shows that the correlation coefficient between the two methods is 0.98,which shows that the four methods to calculate aerosol scaling height are feasible.2.Calculation of aerosol optical depthFirst,surface extinction coefficient can be retrieved by using the observation data which is probed by lidar horizontally;Then the surface extinction coefficient is combined with scaling height by lidar to calculate atmospheric aerosol optical depth.3.Comparion and verificationThe optical depth obtained from the aerosol scaling height and surface extinction coefficient is compared with that measured by sun-photometer in the same area simultaneously.It turns out that the maximum relative error is 13.4%,the minimum is 0.3%,and the average less than 6.7%which means a good agreement.So it is feasible to calculate aerosol optical depth by aerosol scaling height.This method provides a new technological means to calculate atmospheric AOD during the partly cloudy conditions and the night.