Pure Rotational Raman Lidar For The Measurement Of Atmospheric Temperature In The Bottom Of The Troposphere

Temperature is a key parameter to describe the state of the atmosphere.Lidar(Light detection and ranging)provides a comprehensive understanding of atmospheric temperature with high accuracy and high temporal and spatial resolution.With the support of 863 national key project of multisource spectral tomography and three-dimensional numerical atmosphere technology,we have successfully developed a multi-functional and multi-channel laser lidar system.It can simultaneously,continuously and accurately observe the atmospheric temperature,water vapor and aerosol at the bottom of the troposphere.The continuous observation of the variation temperature in Hefei and Beijing prove the lidar system operated reliable and stable.The main research contents are as follows:(1)At the beginning of the thesis,we describe fundamental principle and basic system structure of lidar,and the various lidar detection technology.A summary of atmospheric temperature distribution and its common detection methods have been given in this section.Then,this section recommends the typical atmospheric temperature detection lidar and gives a brief overview of their developments of domestic and overseas.(2)In this article,a set of lidar system that makes use of two pure rotational Raman signals,the vibrational Raman water vapor signals and the elastic signals for the measurement of atmospheric temperature profile,water vapor and the particle extinction coefficient and backscatter coefficient,respectively.As radiation source,a flash-lamp-pumped Nd:YAG laser with a output power of 300 mJ at the frequency-tripled wavelength of 355 nm and a pulse repetition rate of 20 Hz is used.In addition to the fundamental wavelength at 1064 nm,the laser emits radiation at 532 run by frequency doubling simultaneously,which used to detect aerosol.The receiving telescope is a Cassegrain type with a primary mirror diameter of 450 mm and an effective focal length of 4 m for atmospheric temperature and water vapor,and a primary mirror diameter of 300 mm for aerosol.The multicavity interference filters aer mounted sequentially at small angles of incidence.Characteristics of this design are high signal efficiency and high suppression of the elastic backscatter signal in the rotational Raman detection channels.The data acquisition is the transient recorder of Licel.The data of each channel are recorded in analog and photon-counting mode simultaneously.(3)In this dissertation,we mainly analyzes the optimal selection of the filter parameters.In these simulations,we calculated the statistical temperature uncertainty for different central wavelengths of the filters and filters width at different atmospheric temperatures T.The emission at 355 nm is most suitable because of high rotational Raman backscatter cross-sections and higher detector efficiencies at this wavelength.It is advantageous to use 532 nm as the primary wavelength for a system aiming at high performance in the upper troposphere and in the stratosphere,whereas 355 nm is better suited for temperature measurements in the lower troposphere.There is thus an advantage for a UV primary wavelength that it is easier to detect atmospheric temperature in the daytime.The performance simulations show that we can improve the syetem sensitivity by changing ?CWL22 by selecting the angle of incidence.(4)The measurements with the lidar system were made in Hefei and Beijing.The lidar rotational Raman temperature data and the measurements of a nearby radiosonde were in close agreement in the troposphere which can validate the reliability of our lidar system.The continuous observation results show obvious variable characteristics for different height range of the atmosphere.(5)The influence of the 1-? uncertainty of a photon counting signal,different spatial and temporal resolutions and the calibration constant on the statistical temperature uncertainty is discussed.The longer cumulative time,the higher signal-to-noise ratio.When the number of cumulative emission pulse is 10000(5000),the statistical uncertainty of the rotational Raman temperature is about 1.09 K(1.33 K),0.83 K(0.85 K),0.78 K(0.79 K)and 0.88 K(0.89 K)with the different spatial resolution 30 m,60 m,120 m and 240 m,respectively.The calibration constants a and b not only affect the translation of the temperature profile,but also hava an impact on the shape of the profile.The calibration constant c only have an influence on the translation of the profile.When the calibration constants a,b and c have the same changing trend,it has little influence on the temperature and the error has the tendency to cancel.When the calibration constants a,c and b changes in the opposite direction,the error caused by the temperature inversion is larger.