Near-Surface Water Vapor Profile Detection Technology Based On Continuous Wave Imaging Lidar

Water vapor is the key factor of the atmosphere,and its spatial space distribution and concentration changes have an important impact on weather,atmosphere,and environment.The water vapor is mainly distributed in the abutment of the near ground,and has severe changes in the influence of the region,temperature and wind field.Therefore,the development of highprecision near-surface water vapor concentration detection is of great significance to improve the accuracy of weather forecasts,reduce major meteorological disasters,and carry out artificial weather modification.For water vapor detection,the currently used methods such as sounding ball detection,microwave radiation detection methods,and infrared hyperspectral atmospheric detection methods cannot obtain the fine concentration variation curve—profile information on the detection path.However,although narrow-pulse backscatter lidar can obtain fine water vapor concentration profiles,it has a certain detection blind area and cannot detect water vapor within 500m near the ground.Continuous wave imaging lidar is a lidar system that uses a high-power continuous light laser as the detection light source and realizes distance resolution by pixel position resolution through a lateral image sensor.It can obtain the profile information on the detection path,and has made certain progress in atmospheric aerosol detection.It has the characteristics of compact structure,low cost,and small detection blind area.This thesis launched a continuous wave imaging laser radar,and the main work is as follows:(1)An in-depth analysis of the lateral backward imaging detection theory combining the Scheimpflug principle and the hinge principle is carried out,as well as differential absorption laser radar profile detection methods,which lay the theoretical basis for continuous wave imaging laser radar.(2)The scheme of continuous wave imaging lidar system is designed.In order to suppress the divergence angle of the diode laser,the collimation of the laser is realized by using the orthogonal cylindrical lens group,and the divergence angle is reduced fro m the initial θ⊥=35°and θ‖=80 to 0.26mrad and 0.21mrad;in order to realize the differ ential detection system,the dichroic mirrors combines the λon and λoff laser beams,as t he same time selects the appropriate dichroic mirror parameters;a lens group with Galil eo structure is designed,which realizes 9.39 times beam expansion of the combined las er,meeting the needs of imaging detection.(3)According to the scattering and absorption characteristics of the gas,λon=935.68nm andλoff=880nm are selected as the differential absorption detection wavelength pair of water vapor,and select IMX464,which is sensitive to near-infrared light,as the imaging unit.Based on the selected laser power,wavelength and detector parameters,the performance of the system echo signal and detection distance is simulated and studied,and the influence of factors such as the interval and angle between the emitted beam and the imaging unit on the detection performance is analyzed.The simulation results show that the designed detection system is expected to achieve water vapor detection within 2.2km with a concentration of 5g/m3.(4)Based on the system scheme and simulation results,a continuous wave imaging lidar system was initially built;in order to ensure the stability of the laser beam,a closed-loop temperature control module was designed,so that the temperature stability inside the semiconductor laser is ±0.02℃ for 4 hours,and the stable output of the laser wavelength can be realized;according to the imaging detection results,an image processing flow is designed.After background subtraction,filtering,resampling and segmental fitting,etc.,combined with the concentration inversion formula,the water vapor profile can be obtained from the image information;In order to verify the water vapor detection performance of continuous wave imaging lidar,a detection experiment was carried out,and the water vapor concentration at 400m on a certain day is 6.08g/m3,which is basically consistent with the data of other detection sources;Two different directions of water vapor content were detected with lasers,and a significant increase in water vapor concentration was observed at locations with abundant water sources,which preliminarily verifies the effectiveness of the water vapor detection of this system,and the detection capability is expected to be further improved by adding collimation and filter components.The continuous wave imaging lidar system designed in this thesis has the advantages of easy implementation and low cost,and can obtain the water vapor profile near the surface.It is a supplement to the narrow-pulse lidar,which is of great significance to the development of water vapor detection and the study of climate and environmental changes.