Improvement And Verification Of DOTLRT Microwave Radiative Transfer Mode

Spaceborne passive microwave remote sensing plays an increasingly important role in atmospheric exploration and meteorological applications.On the one hand,it can invert the observed atmospheric radiance data to obtain important meteorological parameter products such as global atmospheric temperature,humidity,cloud water,rainfall,ice and snow.On the other hand,satellite microwave data can also be directly assimilated into the NWP(Numerical Weather Prediction)numerical model to improve numerical weather prediction performance.Radiative Transfer Mode plays an important role in both atmospheric parameter inversion and data assimilation applications.Radiative Transfer Mode is used as an observation operator to link atmospheric physical parameters with satellite observation radiance data.The accuracy of it calculating Radiative Transfer directly affects assimilation performance and inversion accuracy.Thus Radiative Transfer Mode is the basic theory and key technology in atmospheric microwave remote sensing applications.At present,under strong convective weather conditions,such as typhoons,heavy rain,snowfall,etc.,the scattering effect of multi-phase water condensate particles in the atmosphere will have the most important impact on satellite observating microwave brightness,which is the most complex part in atmospheric microwave radiative transfer calculation.DOTLRT(Discrete Ordinate Tangent Linear Radiative Transfer)is a microwave radiative transfer mode developed by two scientists of NOAA(National Oceanic and Atmospheric Administration)in the United States,which are Gasiewski and Voronovich.DOTLRT uses the discrete ordinate method and the cascade method to realize the fast analytical solution of the microwave radiative transfer equation and the Jacobian matrix calculation.This mode includes the scattering effect of multi-phase water condensate particles,which can be used for radiative transfer calculations in cloud-rain weather.However,the DOTLRT model only considers the absorption of water vapor,oxygen,and nitrogen in the calculation of atmospheric absorption,without considering other atmospheric trace gas components.In the calculation of atmospheric scattering,only the HG(Henyey-Greenstein)approximation formula is used to calculate the scattering phase matrix.Complete MIE phase matrix calculations are not implemented.In addition,the computational accuracy of the DOTLRT model has been lacking in detailed quantitative research,which limits its application.Based on the in-depth understanding of the atmospheric microwave radiative transfer equation and the realization process of the atmospheric absorption module and the scattering module in the DOTLRT mode,the two modules are improved respectively,and the accuracy of the DOTLRT model for atmospheric radiative transfer calculation is improved.The comparison of satellite real observation data quantitatively analyzes and verifies the calculation accuracy of DOTLRT radiative transfer mode.For atmospheric absorption calculation,this paper obtains the trace gas spectral parameter datas from HITRAN database,and adds the absorption line of various atmospheric trace gases to microwave radiation to the gas absorption module of DOTLRT mode by line-by-line integration method;for atmospheric scattering The MIE scattering phase matrix is calculated by Mie scattering theory and added to the scattering module.Compared with the original HG scattering phase matrix,the MIE scattering phase matrix is better in scattering calculation in most cases.Finally,the observed brightness temperature data of the microwave detector ATMS is used to verify and evaluate the DOTLRT model with reference to the CRTM(Community Radiative Transfer Model)fast radiative transfer mode used by the current US business numerical weather prediction system.The results show that the calculation accuracy of DOTLRT mode radiation transmission is better than CRTM mode in most frequency channels of microwave atmospheric detector ATMS,especially in window channel and water vapor absorption channel;DOTLRT mode in channel 17~22 analog error versus CRTM mode,the maximum reduction is more than 25%,and the simulation performance of most channels in the tropospheric temperature detection channel is equivalent,which fully proves the accuracy of DOTLRT mode in radiative transfer calculation.