Research On The Theory And Method Of Global Ionospheric Modeling For BDS

Ionospheric delay is the main error source of satellite navigation system.The Bei Dou navigation satellite system(BDS)has been developed from the regional navigation satellite system(BDS-2)to the global navigation system(BDS-3).Meanwhile,the service scope of BDS has expanded from region to globe.The constellation of BDS-3 has the characteristics of global coverage and regional heterogeneous.The satellites broadcast S band and L band signal simultaneously.Focusing on the theory and method of the ionosphere modeling,this article studies the BDS-3 observation data quality,differential code bias(DCB)estimation,ionospheric Total Electron Content(TEC)estimation,BDS global ionospheric modeling and Bei Dou Global Ionospheric delay correction Model(BDGIM)performance evaluation,etc.The main research and innovations are as follows.1.The DCB resolving algorithm with BDGIM model constraint is proposed to estimate of absolute ionospheric TEC.The DCB accuracy of BDS-3 new signal is better than 1.0ns.This method does not depend on the external high-precision ionospheric products,and can be applied to the real-time DCB calculation of satellite and receiver with single station.2.Taking the characteristics of GEO,IGSO and MEO in the BDS constellation,as well as the different velocity and orbital planes into consideration,a comprehensive evaluation method of the ionospheric TEC precision based on the TEC comparison of the adjacent ionospheric pierce point and the diurnal jump is designed.This method is used to analyze the accuracy of ionospheric TEC estimated with B1I/B3I carrier phase smoothing pseudo-range dual frequency combination,and the result is better than 3.0TECu.3.An improved inverse distance weighted interpolation(IDW)method is proposed,in which the ionospheric delay gradient anisotropy along latitude and longitude is taken into account.A long-term experiment during spring vernal and summer solstice,autumnal equinox and winter solstice for 12 consecutive years is analyzed to assess the interpolation accuracy.The results show that the precision improved by about 25% than the traditional IDW interpolation for IGS-GIM products.4.The Kriging interpolation method is proposed by taking the impact of outliers into consideration.With IGS-GIM products and GNSS dual-frequency observations during the spring vernal and summer solstice,autumnal equinox and winter solstice in 2014.The result shows that the method can effectively control the impact of outliers,and the global interpolation accuracy is about 1.0?4.0TECu,which is better than the improved IDW interpolation method.5.BDS global ionospheric modeling with BDGIM model constraints is proposed to overcome the limitation of the insufficient sparse distributed BDS ground tracking stations.Taking BDGIM model as virtual observations to constrain the spheric harmonic function(SHF)model,and the SHF parameters were estimated with an interval of 5min in simulated real-time mode by the square root information filtering,the BDS global ionospheric modeling accuracy is about 2.0?5.0 TECu,which is about 6.5% better than that of the BDGIM model.6.The evaluation index of BDGIM performance is constructed.Taken the IGS-GIM products and GNSS dual-frequency observations as reference,the accuracy of BDGIM model is better than the Klobuchar model of GPS.The root mean square error of BDGIM in the global scope is 4.0 TECu,and can reduce the ionospheric delay by about 75%.7.Focusing on the new signal system of BDS-3 satellite,the quality of observations at each frequency is analyzed in detials,and the results can be regareded as a reference for the optimization of observation combination for ionospheric TEC study.With data of BDS-3 satellites,the result shows that the pseudo-range multi-path error at each frequency of BDS-3 is ranging from 0.11 m to 0.27 m.The elevation angle dependent satellite induced multi-path effect in B1I and B3I of BDS-2,has been almost eliminated for BDS-3.The observation noise of carrier phase at each frequency of BDS-3 satellite is ranging from 0.11 mm to 0.37 mm.