Recognition And Application Of Cloud Base Height Based On Coherent Doppler Wind Lidar

Clouds cover approximately 50%to 60%of the earth's area and play an important role in regulating the earth's climate and water cycle.Due to the profound impact of clouds on the atmospheric water balance and the Earth's radiation budget,small changes in cloud characteristics can change the climate response related to greenhouse gases,anthropogenic aerosols or other factors related to global change.Therefore,the accurate observation of cloud vertical distribution,velocity and direction in the vertical direction is very important to understand the influence of cloud on the earth's radiation balance and water vapor cycle.The first prerequisite for accurate observation of clouds is to accurately detect the position of clouds.Coherent Doppler wind lidar is one of the most widely used detection methods for detecting wind speed in existing equipment.However,most of the existing coherent Doppler wind lidars only output wind speed data and carrier to noise ratio data,and do not have the function of output cloud bottom height.Therefore,this thesis takes the inversion of the cloud base height from the coherent Doppler wind lidar carrier-to-noise ratio data as the main research objective.Based on the comprehensive analysis of the characteristics of carrier to noise ratio data,the lidar echo signal is used to invert the cloud base height.The threshold method and differential zero crossing method of lidar echo signal retrieval of cloud base height are organically combined and transplanted to the inversion of carrier to noise ratio data Noise and other thresholds are used to screen carrier to noise ratio(CNR)signal,which is used to distinguish cloud layer,aerosol layer and noise;Then,using engineering language,the software visualization of inversion method is realized,and the existing wind speed data are organically combined to realize synchronous judgment and output of results;Based on the scanning detection wind lidar,vertical detection wind lidar and multi comprehensive comparative observation experiments were carried out under different weather conditions,The universal applicability of the inversion method and visualization software is verified.Through the comparative analysis with multi wavelength lidar,the correlation of cloud base height detected by the two lidars is more than 0.85,which verifies the accuracy and reliability of the method and visualization software.This study proves that the algorithm of retrieving cloud base height using wind lidar carrier to noise ratio is feasible and accurate for different weather conditions(cloudy and cloudless),which can effectively distinguish aerosol layer and cloud layer,and has sensitivity and accuracy for multi-layer cloud judgment.The integrated software can accurately,automatically and real-time extract the cloud base height and cloud base vertical motion velocity,enrich the existing wind lidar functions,provide more comprehensive data products,have certain reference value and application prospects in improving the work efficiency of output cloud parameters,and provide methods and technical support for further detection and evaluation of cloud precipitation potential.