Validation Of The Scheimpflug Lidar Technique And Its Application In Overlap Factor Calibration

Atmospheric aerosols,as a dispersed system suspended in the atmosphere,affect the balance of the earth's radiation budget and regional climate change,and have great research value in the field of meteorological environment and ecology.In addition,the PM2.5 and PM10 aerosols emitted by industrial facilities are the key monitoring targets for environmental pollution control because they can cause harm to human body.Atmospheric Lidar,as an active remote sensing detection technique by making lasers interact with atmospheric components,has advantages that other technologies can't match in real-time and accurate remote sensing detection of the atmosphere and studying the distribution of atmospheric components and their microphysical properties.Atmospheric lidar technique which is based on the Time-of-Flight principle,distinguishes the measurement distance by recording the flight time of pulsed laser signals.It requires the use of complex,high-energy pulsed lasers,high-speed transient recorders,high-voltage photoelectric sensors and other expensive equipment.The cost is high and it requires regular maintenance by professionals,and technological development is facing a bottleneck.As a lidar technique that has developed rapidly in recent years,Scheimpflug Lidar technique provides a new idea for atmospheric remote sensing detection.The technique is based on the Scheimpflug Principle,using a semiconductor continuous light laser as the light source,and a compact area array sensor as the detector.It has the characteristics of low cost,simple maintenance,and compact structure.Relying on the rapid development of semiconductor technique,this Lidar technique has great potential.The measurement principle of SLidar technique is different from that of mainstream pulsed lidar technique.The comparative study of the two is particularly important for the continued development of SLidar technique,which helps to further understand the Scheimpflug principle and the influence on the signal result.In this work,we conducted a contrastive measurement experiment between the self-built532 nm single-wavelength pulsed lidar system and the 520 nm single-wavelength SLidar system.The two systems measured the atmosphere synchronously at the near horizontal direction and a slant direction which the elevation angles is 30°.For the data in the horizontal direction,the Douglas-Puck algorithm is used to find the boundary value,and the Klett algorithm is used to retrieve the extinction coefficient.The comparison results show that although the SLidar signal will be sort of distorted compared to the pulsed Lidar signal after 2km,the signal curves of atmospheric backscatter measured by the 520 nm SLidar system and the 532 nm pulsed lidar system are generally consistent.The Mean Absolute Percentage Error(MAPE)of each signal curve at each distance,and Root Mean Squared Error(RMSE)of the entire measuring distance over time are evaluated,and the average MAPE at the distance of0.3-2.5 km measured by lidar is 0.348% under the horizontal atmospheric condition.In the contrastive study of the slant detection,the MAPE between the SLidar curve and the pulsed lidar curve is 0.45% at the distance of 0.5-2 km.The results show that the SLidar technique with short near-end blind zone is suitable for aerosol remote sensing detection,especially for remote sensing under planetary boundary layers.In addition,a new experimental method was tried.We employed the SLidar system as the auxiliary system of the Mie scattering pulsed lidar system and the ratios of the pulsed Lidar signals to the close range signals measured by SLidar are regarded as the geometric overlap factor of the pulsed Lidar.It is found that in an environment with uniform atmospheric composition,the geometric overlap factor calculated by the proposed method is very consistent with the geometric overlap factor obtained by directly using the signal linear fitting method,and the difference is less than 10%.On the other hand,the SLidar system is used to measure the near-end atmosphere,while the pulsed lidar system measures the far-end atmosphere at the same time.By bonding the lidar curves measured by these two systems,the measurement range of lidar technique is expanded in a more convenient way.The extinction coefficient of nearsurface aerosols from 90 m to 28 km can be well inverted.This work demonstrates the great potential of using SLidar technique to calibrate the overlap factor and extend the measurement range of pulsed lidar technique.