Research On The Solar-blind Raman Lidar For The Measurement Of Atmospheric Water Vapor

Atmospheric water vapor is an important atmospheric parameter,which has three phase changes in the atmosphere.The distribution and variation of the water vapor give a large impact on human activities.The measurements of atmospheric vapor play an important role in understanding the processes of atmospheric water cycle and in revealing the laws of atmospheric motion.Raman lidar can provide the profiles of atmospheric water vapor with high-precision and high-efficiency,which can be used for atmospheric environment research,weather forecasting,and natural disaster warning and forecasting.In this paper,aiming to realize the daytime measurements of atmospheric vapor,the techniques of solar-blind ultraviolet Raman lidar is studied,which utilizes the quadruple frequency output of 266.0 nm as the excitation light source.The spectra of the vibrational Raman scattering signal of oxygen,nitrogen,and water vapor are 277.5 nm,283.6 nm,and 294.6 nm respectively,which are within the range of the solar-blind region.Therefore,there is no effect of sun background on the daytime detection of water vapor using solar-blind Raman lidar,but it suffers from the ozone absorption,which not only affects the detection range,but also influences the data inversion of water vapor mixing ratio.Compared to the Raman lidar with other wavelength,the solar-blind UV Raman lidar needs to extract the vibrational Raman scattering signal of oxygen,which can be used to retrieve the real-time ozone concentration using Raman differential absorption method and to correct the retrieved atmospheric water vapor mixture ratio.In this paper,the solar-blind UV Raman lidar is developed,which utilized the quadruple frequency 266.0 nm of the Nd:YAG laser(SGR-20 model,LeiBao Company)as the excitation wavelength,with the laser energy of 100 mJ and the repetition frequency of 10 Hz.A Cassegrain telescope was selected as the receiver,which has the receiving aperture of 400 mm and the focal length of 3000 mm.A high-resolution spectroscopic system constructed with the high-resolution grating and narrow-bandwidth planar UV reflectors is designed,aiming to separate and extract the Mie-Rayleigh scattering signals and the vibrational Raman scattering signals of oxygen,nitrogen and water vapor.Meanwhile,the system performances,including the effects of sun-background spectra,atmospheric transmittance,and the ozone concentration and the fluorescence spectra,are analyzed.The system simulation results show that the designed solar-blind Raman lidar system has the capability of measuring the atmospheric water vapor up to 2 km in daytime operation under the condition of ozone concentration of 30 ppb.Finally,the solar-blind Raman lidar system is built for atmospheric vapor detection based on the existing instruments and equipment in the laser radar center of remote sensing of atmosphere at Xi 'an University of Technology.The experimental data showed that the system can detect the atmospheric water vapor up to the height of 1.2 km with an accumulation of 10000 laser pulses(16.7 minutes),which verified the feasibility of the system.