The Key Technologies And System Experiments Of High-Spectral-Resolution Lidar

Atmospheric aerosols have significant impacts on the global environment and climate,thereby directly or indirectly affecting human activities.The high-precision detection of atmospheric aerosol characteristics not only has a fundamental guiding role in clarifying the causes,evolution,and transmission mechanism of atmospheric pollution,but also has important scientific significance for systematic research on climate and meteorology.The high-spectral-resolution lidar(HSRL)has advantages of high temporal and spatial resolution,high theoretical detection accuracy,and high signal-to-noise ratio,compared to the Mie lidar and the Raman lidar in the field of aerosol detection.Therefore,the spaceborne HSRL has received widespread attention from various countries including America,Europe,Japan,and China.At present,there are still many key technologies and difficulties to be overcome in HSRLs.One of the core challenges is achieving high precision and stable detection of atmospheric optical characteristics with HSRLs.Therefore,the development of an HSRL engineering prototype to achieve high-precision and stable detection of atmospheric optical characteristics,and to explore its performance optimization methods,will help promote the widespread application of mature HSRL instruments in the future.Based on the HSRL simulation model,the detection mechanism of lidar,the hardware parameters,the optimization method of spectral discriminators,the scheme of instrument calibration,and validation are explored.Finally,we provide a set of complete solutions to develop HSRL and observe atmospheric aerosols.The main research contents of this thesis are summarized as follows:A multi-wavelength and multi-parameter analysis model of HSRL based on the Monte Carlo(MC)method is constructed.To verify the whole process of HSRL from parameter design to signal retrieval,an approximate model of the system response is proposed,the influence of the system response on the HSRL parameters selection process is clarified,and the HSRL analysis model based on the MC method is established.Using this analysis model,the impact of the spectral discrimination performance and stability of the spectral discriminator on the retrieval accuracy is discussed,and the influence of the channel gain ratio fluctuation on the retrieval accuracy is discussed.The HSRL design at different wavelengths is compared.The difference in demand provides an important basis for the design of HSRL system parameter design and performance optimizationPerformance optimization methods for the key component of HSRL-the spectral discriminator are proposed.Two typical spectral discriminators,the iodine absorption cell and the field-widened Michelson interferometer(FWMI),are discussed in aspects of stability and spectral discrimination characteristics,respectively.Optimization methods in the design of these two spectral discriminators such as optimal selection of the iodine absorption line and pressure-tuned mechanisms of FWMI are further investigated.For the unstable interference-based spectral discriminator,this thesis proposes a pressure-tuned frequency auxiliary mechanism that greatly improves the stability of the system spectral discrimination performance.A prototype of the near-infrared pressure-tuned FWMI spectral discriminator is developed,and the calculation process is depicted.For the selection of iodine absorption line in the 532 nm band,the fast and non-dominated sorting genetic algorithm with elite decision-making is utilized to solve the multi-objective problem,and realize the optimal design of the spectral transmittance parametersA calibration method for the overlap function of HSRL is proposed,which improves the lidar calibration and data quality evaluation scheme.Due to the complexity of the lidar system,it is difficult to perform absolute calibration in measurements.Therefore,to obtain accurate lidar detection results,this thesis comprehensively explains the system calibration scheme,including overlap function calibration,optical axis alignment,gain ratio evaluation,Rayleigh fitting verification,trigger delay correction,background noise test,etc.Among them,given the problem that ground-based lidar low-altitude data is greatly trapped in the overlap function,this thesis proposes an overlap function calibration method based on the iterative optimization idea for HSRL.The overlap function result is compared with the real one detected by the dual-field-of-view HSRL system.The average relative error of this comparison is 4.56%,which proves that the overlap function can be calibrated concisely,efficiently,and accurately.The validation scheme of HSRL was discussed,and the detection results of self-developed HSRL were verified by quantitative comparisons.Combining the above research content,the 532 nm single-wavelength HSRL prototype and the 532 nm-1064 nm dual-wavelength HSRL principle experimental system have been successfully developed.The detection results are compared with the results of different instruments such as the Cloud-Aerosol Lidar with Orthogonal Polarization(CALIOP),in-situ cavity ring down aerosol extinction spectrometer,micro-pulse lidar,Raman lidar,and sunphotometer.The results are all very consistent.The mutual calibration experiment of multiple instruments fully proves that the HSRL instrument can obtain atmospheric optical characteristics with high precision and stability.The two instruments have carried out long-term field experimental detections in Hangzhou,Zhoushan,and Beijing.Through specific analysis of data cases during the detection process,the identification of aerosol types using dual-wavelength aerosol optical characteristics are initially explored.