Research And Design Of Raman Lidar For Profiling The Atmosphere Temperature And Humidity

The change of temperature and relative humidity in the troposphere is closely related to the evolution of climate and meteorology,specially for greenhouse effect the heat island effect,and also to human's production and life.In recent years,some studies have shown that atmosphere temperature and relative humidity are the important factors affecting temporal and spacial distribution atmosphere aerosol mass concentration.Therefore,the detection of atmosphere temperature and relative humidity at vertical height have great significance for studying the atmospheric environment and human health,and can provide the valuable information for weather forecasting and environment monitoring.Based on the lidar laboratory platform of Beifang University of Nationalities,a Raman lidar was developed for the temperature detection by rotational Raman scattering and the water vapor detection by vibration Raman scattering based on the narrow-band interference filters.In the lidar system a Nd: YAG pulsed laser emits a 532 nm pulsed laser beam with 10 Hz and 450 mJ.Through collimated and expanded,the laser beam is reflected by several mirrors and directed vertically into the atmosphere.After the laser light interacts with the molecules and particles in the atmosphere,the back scattering signals are received by the a Cassegrain telescope with diameter of 400 mm and focal length of 1000 mm.Through converged by a lens,the return signals are coupled into a multi-mode fiber(MMF)and transmitted through the spectroscopic system.In the spectroscopic system some return signals filtered by the 660 nm narrow-band interference filter are taken by a photo-multiplier tube(PMT),which is the water vapor channel,and some extracted by the 607 nm narrow-band interference filter are taken by a PMT,which is the nitrogen channel.The other signals drawn by the 529 nm and 530 nm narrow-band interference filters are detected by two PMTs,respectively,which corresponds to high and low quantum number rotational Raman signals and used to retrieve the atmosphere temperature.The outputs of PMTs are directly connected with the high-gain,low-noise and high-speed amplifiers,which plays the role of impedance matching and signal amplification.Through the amplifying circuit all signals are taken by a data acquisition and processing system.Moreover all PMTs work in the analog mode and the response time of acquisition system is about 300 ns,which corresponds to spatial resolution rate of 45 m.In the lidar system the Mie and Rayleigh signals are suppressed with 10-7rejection rate and the the weakly rotational Raman signal and the vibration Raman signal are extracted accurately,so as it realize the fine detection of temperature and water vapor profiles in the atmospheric boundary layer.Moreover in order to facilitate the observation of the measured temperature and relative humidity,the software of data acquisition and processing based on LabView are developed,by which the profiles of atmospheric temperature,water vapor mixture ratio and the relative humidity of can be seen clearly.Some experiments were performed to verify the feasibility of the Raman lidar at Beifang University of Nationalities(E'06106?,N'2938?)in Yinchuan,China.In experiments the data acquisition time is set to about 16 minutes and the number of laser pulses is 10000.The experiment results show that for temperature the effective detection height are from 0.3 to 3.5 km in the daytime,and for and relative humidity the effective detection height of is from 0.3 to 3 km during the day and from 0.3 to 4.5 km at night.