Lidar System Design For Absolute Detection Of Atmospheric Temperature In Whole Day

Atmospheric temperature is one of important meteorological parameters in atmospheric physics,atmospheric science and space environmental monitoring.The rotational Raman lidar is a kind of remote sensing method for temperature detection with relatively simple structure,moderate difficulty in spectral spectroscopy and the ability to eliminate the influence of elastic scattering signals.It has become one of important instruments on detecting atmospheric temperature profile of the bottom layer.Based on the Raman scattering principle of atmospheric molecules,we analyzs wavelength shifts of rotational Raman spectral lines with respect to the emitted laser light in this thesis.Therefore,it is not interfered by the strong elastic scattering signal of the aerosol in the atmosphere,and high-precision detection of atmospheric temperature profiles in the bottom layer could be realized.According to the relationship between the intensity of the rotational Raman backscattering cross section and the atmospheric temperature,the atmospheric temperature profile is retrived,and then the design and analysis of key parameters of the lidar are carried out.For the core two-stage spectroscopic system,F-P interferometer(FPI)is used as frequency comb filter,of which full width of half maximum(FWHM)is chosen as 6 pm by analyzing the fine spectral structure of nitrogen(N2)molecules.Considering the current processing level of FPI,such as the coating loss and the manufacturing defects,the rotational Raman spectral lines of the even rotational quantum number of N2 molecules in Anti-Stokes branch is optimized and matched to effectively filter the solar background noise and the adjacent Raman spectral lines.The Raman spectral lines of 8-channel even-rotational quantum number(J=6-20)is optimally extracted by using the spatial light dispersion of the low-order blazed grating and the fiber line array.Since the processing precision of FPI mirror spacing is about 0.5 ?m,it is difficult to achieve precise matching of rotational Raman spectral line and FPI by only seed laser inj ection tuning,and hence the performance analysis of FPI tuning mode is discussed(including PZT,pressure,angle,temperature tuning),a combined tuning scheme of seed laser injection and FPI angle adjustment is proposed to efficiently extract the Raman spectral lines of 8-channel even-rotational quantum number(J=6?20).The structural parameters of the entire lidar were optimized.Then the detection performance of the lidar was analyzed during the whole day by using the standard atmospheric model and the existing retrival algorithm.Theoretical research and analysis results show that the spectroscopic system can achieve about 60 dB suppression of the elastic scattering signal,and the transmittance of the 8 rotational Raman channels respectively is 0.265?0.440'According to the absolute atmospheric temperature detection and retrival algorithm,the system can realize the without-calibration absolute detection of atmospheric temperature profile of 1.2 km or more at night and 0.8 km(statistical error is 1 K)at daytime during a measurement period about 17 minutes.It may provide a new spectroscopic scheme and technical means for high-precision lidar remote sensing detection of atmospheric temperature in the whole day.