Studies On The Polarization Filtering Technology For The Scheimpflug Lidar

With the rapid development of our country's economy and society.Environmental problems are becoming more and more serious,and the air quality is declining gradually,it is urgent to carry out the air environment monitoring by powerful technical means.Lidar technology has many advantages,such as strong anti-jamming ability,high detection sensitivity,high spatial resolution and wide measurement range,which has become one of the important means of atmospheric environment monitoring.Pulsed atmospheric lidar technology based on the principle of time-of-flight has been developed rapidly and widely used in atmospheric remote sensing.Although the pulsed Atmospheric Lidar technology is powerful and has excellent long-range detection capability,it still faces the application bottleneck of complex system,high cost and cumbersome maintenance.In recent years,scholars have proposed a new type of Scheimpflug lidar(SLidar)technology,based on Scheimpflug principle.This technology uses image sensor as the detector and laser diode as the light source.It can realize the range-resolved detection of the atmospheric echo signal by clearly imaging the laser beam emitted into the atmosphere under the condition of Scheimpflug imaging.SLidar technology has the characteristics and advantages of compact structure,good stability,simple maintenance,low cost and so on.It has important application value in the field of atmospheric environment monitoring.Because of using continuous wave laser diode as the light source,the peak power of SLidar technology is low.As a result,the atmospheric echo signal is greatly affected by the sunlight background during daytime detection.Although it can realize all day detection,the signal-to-noise ratio of atmospheric echo signal is still poor under the condition of strong background radiation.The scanning SLidar technology needs fast scanning speed(such as 6-12°/min)for atmospheric pollution monitoring.Thus,the average time of a single lidar signal is limited,which makes it difficult to improve the signal-to-noise ratio of lidar signal by increasing the average time.Therefore,further suppressing the background noise of sunlight and improving the signal-to-noise ratio(SNR)of the air echo signal of SLidar technology are of great significance for the practical application of the SLidar technology,especially for applications requiring rapid scanning speed.Single-wavelength scanning SLidar systems at 808 nm are susceptible to solar background radiation.When the solar radiation is strong,the background intensity is relatively large,and the corresponding atmospheric echo signal has poor SNR,which seriously affects the detection performance of the system.Therefore,how to further suppress the background noise of sunlight and improve the SNR of the atmospheric echo signal of SLidar technology become an urgent problem to be solved in the practical application of SLidar technology.In order to solve this problem,a polarization filter technique utilizing the polarization characteristics of solar light is presented and applied to the detection of atmospheric echo signals with SLidar technology.Linear polarizer can suppress the background intensity of the sun,thereby improving the SNR of the atmospheric echo signal of SLidar technology.The influence of the zenith angle of the sun on the SNR improvement coefficient of the vertical pointing lidar system is also simulated with MATLAB.This paper will start from the following aspects.Chapter 1 outlines the technical background of atmospheric lidar and its research status.Chapter 2 introduces the basic principle of the SLidar and the main sources and characteristics of the noise.Chapter 3 theoretically simulates the influence of the solar zenith angle on the SNR of the atmospheric echo signal for the vertical pointing lidar.Chapter 4 presents experimental results based on the single wavelength scanning SLidar system by improving the detection unit of the system.Simultaneous detections of un-polarized differentiated atmospheric echo signal and horizontally polarized atmospheric echo signal has been realized,and the feasibility of using polarization filtering technology to suppress the solar background noise in the case of strong sunlight background radiation in the daytime is studied.Finally,the main research work of this paper is summarized and the future work is outlined.