Research On Synchronous Detection Technique For Atmospheric Three-phase Water By Using Raman Lidar

Water is the only atmospheric parameter with three-phase states.As one of the most active components in the atmosphere,water vapor has obvious temporal and spatial variation characteristics,and is an indispensable factor in the process of cloud formation and precipitation.Atmospheric water vapor and liquid water content are also important parameters of cloud precipitation physics and play an important role in atmospheric water circulation,atmospheric water balance,and cloud physics.Therefore,the identification and detection of atmospheric three-phase water has important scientific significance and research value for understanding cloud microphysics,cloud precipitation physics and artificial weathering processes.In this thesis,the synchronous Raman lidar detection technique for atmospheric three-phase water is carried out.Aimed at the overlapping characteristics of Raman spectrum in three-phase water,we simulated and discussed in detail the effects of selection parameters of the filters on spectral overlap degree and detection signal-to-noise ratio in each Raman channel.Secondly,in the case that the optimal solution cannot be achieved at the same time,we proposed an evaluation function method using multi-objective programming problem,in order to obtain the optimal filter parameters of each channel.The results show that,when the center wavelength and bandwidth of the narrow-band filter of solid water,liquid water and water vapor channel are designed with 397.9 nm(3.1 nm),403 nm(5 nm)and 407.6 nm(0.6 nm),the lowest spectral overlap value and the best detection signal-to-noise ratio can be obtained in three-phase water Raman channels,and thus the optimal spectroscopic system design was realized for synchronous detection of three-phase water.Aiming at the crosstalk problem of three-phase water Raman scattering echo signals,we also proposed a synchronous inversion method for atmospheric three-phase water mixing ratio profiles based on spectral interference degree,and the corresponding inversion error was also discussed.The results show that the lidar echo signal term is the primary factor affecting the overall error of the three-phase water mixing ratio.Taking 3 km as the reference point,the overall errors for water vapor,liquid water and solid water under cloudy weather during the daytime are 8%,15%and 30%,respectively.A high-performance Raman lidar system was built in Xi'an University of Technology,in which a set of dichroic mirrors and interference filters constitute the main spectroscopic system.Preliminary measurements were carried out and experimental results were analyzed.Several representative results under clear weather,cloud weather and haze weather indicated that the Raman lidar system has successfully realized the simultaneous detection and inversion of atmospheric water vapor below 7 km,liquid water below 5 km and solid water below 3 km.In particular,the simultaneous growth of atmospheric water vapor,liquid water and solid water in the cloud layer can be achieved.In addition,simultaneous continuous observations for three-phase water were carried out,and the spatial-temporal evolution characteristics of water vapor,liquid water and ice water clearly reflected both the drift process of the cloud layer and simultaneous enhancement in the cloud layer.The Raman lidar and the obtained results will provide theoretical basis and data support for the study of liquid water integral and cloud microphysical characteristics in the cloud.