Research On Determination Of Pblh Based On CALIPSO Space-borne Lidar Observations

Aerosols have an important impact on human health,environmental pollution and transportation.In recent years,the problem of air pollution is more and more prominent.The atmosphere boundary layer is the lowest part of the atmosphere,which has most interactions with the surface.The studies on the characteristics of boundary layer has been a hot issue at home and abroad,one of the characteristics of the boundary layer is its height,also called mixing layer height(MLH),the researches on the detection of boundary layer height become an important content for atmospheric detection.However,the traditional methods for detecting the boundary layer height have their limitations,such as low spatial coverage,low repetition frequency or low accuracy.For this deficiency,the ground-based lidar as an active detection technology has become an effective techniques for PBLH(Planetary boundary layer height)detection.In addition,PBLH detection based on CALIPSO(Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations)space-borne lidar has been gradually developed in the past eleven years.Compared with ground-based lidar,CALIPSO has a unique advantage in spatial coverage.Since the backscatted signals acquired by CALIPSO have low signal to noise ratio(SNR),in this paper,the influence of system parameters of space-borne lidar on the SNR of the backscattered signals was discussed,According to the simulation analyses of backscattered signal of space-borne lidar.Then,we analyzed the smooth results by changing the accumulative pulse.Then the retrieval method was discussed.At present,the maximum variance method is the main method for retrieval of PBLH from CALIPSO observations.However,this method can cause misjudgment of PBLH.In addition,the method has limitations for different conditions of atmospheric pollution.The maximum variance technique is more robust for the clean air and partly cumulus convection case,while the wavelet covariance technique is more effective for a turbid atmosphere with high backscattering in the PBL.The improved maximum variance method was developed by increasing the judgment condition.At the same time,an integrated algorithm of determining the PBLH was developed,which characterized by combining the wavelet covariance method and the maximum variance method.The PBLH results over China region were derived by the integrated algorithm from CALIPSO observations.Six typical sites were selected to analyze the temporal variation of PBLH in typical region of china.According to the analyses of season and interannual variations of PBLH in china region,the results illustrated the characteristics of PBLH distribution in time and space.Then,the seasonal and interannual variations of PBLH in China region were analyzed by using the reanalysis products ECMWF,and the corresponding results were compared with those of CALIPSO.The main results of this paper are as follows:(1)The PBLHs over Beijing station were retrieved by the ground-based lidar.Then,the PBLH results under different conditions of air pollution,years of diurnal variation,seasonal change and interannual variations were analyzed for Beijing station.The results showed that the PBLHs have certain characteristics of distribution in different time and conditions of air pollution.(2)The simulation analysis of space-borne lidar show that the laser emitted energy,the size of the receiving aperture,and the accumulative pulse are positively correlated with the SNR,while the Filter bandwidth,Receiver Field of View and Digitization Rate are inversely correlated with the SNR.According to the smoothing results of the accumulative pulse,it is shown that the accumulative pulse was positively correlated with the SNR,but the horizontal resolution of the backscattered signals was decreased with the increase of the smoothing scale.(3)The PBLHs derived from CALIPSO were verified by using the PBLH detection results from ground-based lidar stations.The comparisons results show that the mean absolute difference of PBLH for Lille lidar station is 206 m under cloud-free conditons,the mean absolute difference of PBLH decreases to 106 m after removing the alofted layer.Because the mean distance between Beijing ground-based lidar station and CALIPSO track is beyond 40 km,the mean absolute difference of PBLH is 0.5 km for Beijing lidar station.(4)The PBLHs for China region were derived by the integrated algorithm from CALIPSO observations.According to the analyses of temporal variation of PBLH in six typical sites,it illustrated the conditions of air pollution in typical regions of china.According to the seasonal and interannual variations analyses of PBLH in china region,it showed that PBLH has obvious characteristics of seasonal variation.In spring and summer,the PBLHs have high values,while the PBLHs have low values in autumn and winter.The annual variations of PBLHs are not obvious.By comparing the PBLH results obtained by ECMWF reanalysis data,we found that a big difference exists between them.Finally,the PBLH results of ECMWF were revised by PBLH results derived from CALIPSO observations.