Development Of The Lateral Raman Scattering Lidar For Atmospheric Water Vapor Measurement In Lower Troposphere

Atmospheric water vapor is an important parameter to describe the physical state of the atmosphere,which is one of the important greenhouse gases with the active spatial-temporal changes.Water vapor is the only gas in the atmosphere that has phase change,which plays an important role in the global water cycle,weather system,atmospheric physical and chemical changes.Half of the water vapor is present in the atmospheric boundary layer,which is closely related to human activities.Raman scattering lidar is an effective tool for detecting atmospheric water vapor,with the advantages of high precision,high resolution,and continuous observation.However,the traditional Raman scattering lidar utilizes a monostatic transceiver system structure,which results in the blind zone and transition zone of the geometrical overlap factor in the nearsurface atmosphere,and makes the detection of water vapor in the lower atmosphere more difficult.In order to realize the detection of atmospheric water vapor without the influences of the blind zone and transition zone of the geometrical overlap factor,this dissertation proposes a novel lateral Raman scattering lidar system for atmospheric water vapor detection,which employs the bistatic transceiver system structure as the lateral image lidar.This dissertation presents the detection principle,system design,system simulation and preliminary experiments of lateral Raman scattering lidar in detail.Firstly,the dissertation describes the detection principle of lateral Raman scattering lidar,and then analyzes the difference between lateral Raman scattering lidar and backward Raman scattering lidar,and constructs the lateral Raman scattering lidar equation to accurately express the atmospheric water vapor inversion method using the lateral Raman scattering lidar.The bistatic lateral Raman scattering lidar detection system is designed,which adopts the LD-pumped all-solid-state continuous wave laser as the transmitter,and selects a dual optical telescope group as the lateral receiving system,which is placed on the rotation platform with the elevation angle scanning capability.The profile is realized by the scanning of the rotation platform with the elevation angle scanning.The spectroscopic system is integrated at the end side of the telescope outlet.An ultra-narrowband interference filter is used to effectively separate the vibrational Raman scattering signals of nitrogen and water vapor.Further in this dissertation,the system simulation of lateral Raman scattering lidar is carried out,including the lateral scattering coefficient,extinction coefficient,two-way atmospheric transmittance,lateral scattering echo signal intensity and signal-to-noise ratio of nitrogen channel and water vapor channel.The simulation results show that the horizontal distance D between the transmitter and the lateral receiver system affects the virtual pulse length,elevation angle setting,lateral atmospheric transmittance,signal-to-noise ratio and so on.The simulated calculation results of the lateral scattering echo signal and signal-to-noise ratio fully proves the possibility of the lateral Raman scattering lidar system to detect water vapor in the lower atmosphere.Finally,the dissertation presents the system construction and preliminary experimental observations of the lateral Raman scattering lidar.According to the simulation results,the experimental system is built and the experimental scheme is designed.The experiment adopts two sampling schemes of equal distance resolution and segmented equal distance resolution to carry out experimental detection.The experimental results show that both schemes can achieve fine detection of atmospheric water vapor mixing ratio from the ground to the height of 1300 m,and the segmented equidistance resolution sampling scheme can obtain a finer water vapor profile distribution structure near the surface.The lateral Raman scattering lidar can overcome the shortcomings of the blind zone and transition zone of the backward Raman scattering lidar,which provides a new detection technique for the fine detection of water vapor in the near-surface atmosphere.