Single-line-extracted Pure Rotational Raman Lidar To Measure Atmospheric Temperature And Aerosol Profiles

We have built an innovative single-line-extracted pure rotational Raman(PRR)lidar system,the optical system of this lidar adopts the combination of filter and FPI,from which we can effectively detect two isolated N2 molecule PRR line signals(anti-Stokes PRR lines J=6 and 16)and elastic backscatter signal.The article introduces various methods of measuring atmospheric temperature and aerosol optical properties in principle,and emphatically recommend the principle and error analysis of the single-line-extracted PRR method.Furthermore,the design,calibration and testing procedures of this lidar system is introduced in detail.The PRR lidar system was verified and evaluated after its establishment based on two sides:Spectroscopic performance test and the retrieval results.Which certifies that our PRR lidar is a single-line-extracted lidar system.1.Experiment result showed the optical part can generate a suppression of 2 orders of magnitude to the adjacent anti-Stokes O2 PRR J= 7,9,21,23.2.Two parameters that are required for the temperature inversion of the single-line-extracted PRR lidar.One parameter a is a known constant which depends only on the difference of the rotational Raman energies of the two extracted lines,while another b can be obtained by measuring the ratio of the overall efficiencies in the two N2 PRR line channels.Hence the single-line-extracted PRR lidar allows the atmospheric temperature measurements without calibration from reference temperature data(e.g.,radiosonde temperature).The parameters a and b were obtained also via comparison with accompanying local radiosondes.The calibrated a and b values are very close to the theoretical and measured results with respective relative deviations of 0.2%and 3.5%.The perfect agreement validates that our PRR lidar is a single-line-extracted lidar system.Combining the lidar equations for one single-line-extracted PRR signal and elastic signal,we have derived a new analytical expression of the particle backscatter coefficient(or backscatter ratio).It is indicated that the particle backscatter coefficient(or backscatter ratio)can be determined simply from the signal profiles measured in one single-line extracted PRR channel and elastic channel as well as the lidar temperature profile without additional assumptions(e.g.lidar ratio or Angstrom relationship).The particle extinction coefficient is derived further from the acquired particle backscatter coefficient profile and elastic signal profile.The lidar ratio can be obtained then from the derived particle extinction coefficient and backscatter coefficient.The two particle optical parameters as well as resultant lidar ratio provide quantitatively strict standards for the lidar measurements of aerosol and cirrus.Observational examples show the capability for the current lidar to measure all-day atmospheric temperature profiles and aerosol/cloud optical properties.For an altitude resolution of 150 m and a time resolution of 60 min,the temperature measurement altitude at nighttime reached～6.5 km with the RMS deviation between the lidar and concurrent radiosonde and the statistical uncertainty both being better than 1 K.At daytime the lidar temperature measurement extended up to～2.6 km with the RMS deviation and statistical uncertainty both not exceeding 1 K.Based on the strict analytical expressions derived from the lidar equations for the single-line-extracted PRR channel and elastic channel,the optical properties of the urban aerosol,dust layer and cirrus clouds were obtained with the comparison of different aerosol inversion methods(Fernald method and Pure Rotational Raman reference signal method)in lidar.