Near-field Correction And Fine Inversion Technology Of Scanning Mie-raman Lidar

Atmospheric aerosols have had a profound impact on climate change and air pollution.Scanning Mie-Raman aerosol lidar has become an effective monitoring tool for aerosols due to its flexibility,high precision and real-time performance.However,the problem of near-field signal correction restricts its practical application process.Therefore,it is necessary to conduct related research on lidar near-field signal correction methods.Based on the assumption that the atmosphere is horizontally and evenly stratified,a vertical scanning near-field signal correction strategy and a multi-angle data fusion scheme based on the SNR threshold are proposed,and data acquisition,processing and control software are compiled according to the status of each module in the scanning acquisition process system.Realize the fine inversion of near-field signals without blind zone.Based on the basic parameters of the scanning Miraman lidar system,the system overlap factor model was established,and the effects of laser beam divergence angle,telescope receiving angle,initial distance of optical axis,and optical axis inclination angle on the overlap factor in the non-overlapping area were analyzed,and passed The comparison of the measured data verified the horizontal correction method of the overlap factor;using the Fernald aerosol inversion algorithm,a vertical scanning near-field signal correction strategy based on the signal-to-noise ratio was proposed,and the state conversion and multi-angle data fusion method of each module of the acquisition process system was designed to cooperate,the aerosol extinction coefficient data in the effective detection interval of the multi-angle slope detection is fused to ensure the effective implementation of the near-field correction strategy.Comparative analysis of the detection echo signal preprocessing method,on the basis of the traditional random noise denoising method,the CEEMDAN-WT joint denoising method is used to denoise the echo signal,the signal-to-noise ratio after processing is compared with the single WT denoising The noise method is improved by about 1dB,the root mean square error is reduced by 36%,and the smoothness is increased by 10%.Based on the signal preprocessing method and the near-field signal correction strategy,the signal acquisition processing and control software is compiled to realize the cooperative control of each module of the scanning acquisition process system and multi-angle data fusion.When the horizontal visibility is better than 18km in static and stable weather,with the signal-to-noise ratio of 20dB as the threshold,the multi-angle scanning detection data is used to correct the vertical detection near-field signal,and the obtained overlapping factor correction curve and the average of the horizontal detection method correction curve The relative deviation is about 20%,and the average relative error in the transition zone is about 4.7%.The long-term fixed-point detection data is corrected by the vertical scanning correction result,and the correction result can reflect the change process of the real atmospheric state in the near field with time.Based on the assumption of uniform distribution of near-surface aerosols,the long-term fixed-point slope observation signal is corrected,and the average extinction coefficient of the corrected signal at different evaluation heights is used to calculate the slope visibility,and the short-term average of the horizontal visibility instrument within the measurement time The results are used as the benchmark for comparative analysis,and the calculated visibility results are basically consistent with the trend of the horizontal visibility meter,and the evaluation height is reduced to 50m.Observation experiments and analysis show that the vertical scanning near-field signal correction method and control software can realize the detection of aerosol characteristics without blind spots,and can promote the practical progress of aerosol Mie-Raman lidar.