Decoupling Method And Experiment Research On Gas Rayleigh-brillouin Scattering Envelope Spectrum

In the atmosphere detection,lrdai*has become a povwerful tool for active remote sensing of the atmosphe re with its high detection sensitrivity,high time and spatial resolution.Atmospheric temperature profile detection baserd on Rayleig,h scattering has attracted wide attention of researchers due to its high signal-to-noise ratio.However in general,the laser Iidar echo sitgnal removes the Rayleigh scattering caused by temperature,and there is also Brillouin scattering caused by pressure.The two are mixed and formed to form a Rayleig-Brillouin scattering envelope spectrum,so that it is based on Rayleigh.Tlie scattering of the lidar atmospheric temperature profile is difficult to detect.It is currently accepted that the best mathenmatical model describing the Rayleigb-Brillouin scattering ernvelope is the S6 model,but the model does not have an analytical solution?andnly describes the overall external profile of the Rayleigh-Brillouin scattering envelope spectrum,which cairaot be separated.Temperature-induced Rayleitgh scattering and pressure-ind}ced Brillouin scattering reduce tlie in,ve:rsion accuracy of atmospheric parameters.In order to improve the atbsolute detection accuracy of lidar a.oosph'ric temperature,the external pr.files of Rayleigh-Brillouin scattering envelope spectrLum are described by linear superposition of three Gtaussian functions.The model has independent Rayleigh scattering and Brillouin scatte,ing analytic expressions,and can decouple Rayleigh scattering and Brillouin scattering lines in the envelope spectrum.T he mod.el can retrie.ve the temperature and pressure of the gas.After four discrete imloEmation points on the Rayleigh-Brillouin scattering envelope line are selected to solye the unknown paramceters in the.model,the teyaperature and pressure values of the gas are calculated by using the termpilrature-related,Rayleigh scattering line and pressure-related Brillouin scattering line.In order to verify the application of the model in the detection of atmo-spheric temperature and pressure by lidar,a gas simulation scattering cell is used envelope spectra of different gas temperature and pressure states.The temperature and pressure of the Rayleigh-Brillouin scattering envelope spectra of gases are inverted by using the decoupling model.The independent Rayleigh scattering and Brillouin scattering spectra are obtained by decoupling the envelope spectra.Finally,the absolute error between the temperature value obtained by inversion of experimental spectral lines and the measured temperature value in the experiment is 10.60K,and the absolute error between the pressure obtained by inversion and the measured pressure value in the experiment is±1.00kPa.The results show that the Gauss model can decouple the Rayleigh-Brillouin scattering envelope spectra,decouple the Rayleigh and Brillouin scattering spectra accurately,and invert the temperature and pressure of the gas.It provides a feasible decoupling method for lidar to detect the Rayleigh-Brillouin scattering spectra in the atmosphere.