A Theoretical And Experimental Study Of Cloud Height Detection By Meter Scattering Lidar

Cloud detection affects the atmospheric monitoring,the maintenance of the atmospheric radiation balance,and the analysis of the water vapor cycle.In recent years,the development of atmospheric lidar system provides an effective means for cloud detection.This paper summarizes the previous cloud detection methods and experience based on lidar,developed a set of lidar cloud detection systems and designed the corresponding signal algorithms and software.The lidar signal obtained in the actual measurement is relatively weak,the detection distance of the system cannot achieve the expected effect under the influence of various kinds of noise.In view of the above problems,the research contents of this paper are as follows:Based on the principle of lidar atmospheric detection,a lidar cloud detection system with low cost,miniaturization and good user experience is developed in this paper.The system adopts the design of transmitting coaxial optical path,uses new optical devices to build a compact low-cost small lidar,which can better implement movable detection.To make the device have good human-computer interaction ability,the supporting software of hardware system is designed by using Lab VIEW platform.For solving the problem of weak echo signal of lidar,the characteristic of lidar echo signal and the main source of noise are analyzed.In this paper,Local Mean Decomposition and an improved thresholding method(LMD-ITM)is proposed to overcome the shortcomings of the traditional algorithm such as the end effect and the mode mixing.This method determines whether the component is retained by calculating the correlation coefficient between the component function sequence(PFs)and the echo signal,and the energy entropy.Based on the threshold denoising algorithm,the threshold function and adjustment factor are improved to realize the adaptive effective filtering,and the effective information which is difficult to separate from the high-frequency signal.In order to verify the detection capability of the system,experiments are carried out in the real atmospheric environment.Compared with the traditional algorithm,the SNR of the proposed algorithm is improved by 15%,and the effective detection range is extended by 2km.The corresponding threshold is set according to the atmospheric conditions before and after the period,the differential zero crossing method is improved,which can calculate the cloud base height accurately.The experimental results prove the rationality and effectiveness of the designed lidar system and the proposed method.