Research On Global Ionospheric Modeling Based On Multi-source Data Fusion

The ionosphere is an important part of the solar-terrestrial space environment.Monitoring and studying various phenomena on the ionosphere,and then revealing its temporal-spatial variation characteristics and physical mechanisms,is of great significance in promoting the interdisciplinary research of ionospheric theory and earth science,but also is conducive to the development of aerospace,communications and other applications.The emergence of global navigation satellite system(GNSS)has greatly promoted the development of large-scale,continuous and high-precision ionospheric detection.At present,global ionospheric models are mainly developed using ground-based GNSS data.Due to the uneven distribution of ground-based GNSS tracking stations around the world,especially in marine areas,the existing global ionospheric model has low accuracy and reliability.Aiming at the problem of low accuracy and reliability of the global ionospheric model in the ocean or areas away from the GNSS stations,on the basis of studying GPS/GLONASS data fusion,this paper further integrates satellite altimetry and DORIS data to establish high-precision and high-reliability global ionospheric model.This contribution is outlined as follows.Firstly,the processing methods of GNSS observation data,ocean altimetry data and doppler orbitography and radio positioning integrated by satellite(DORIS)data are researched.Besides,this paper derives the formula for extracting ionospheric TEC from ground-based GNSS,ocean altimetry satellites and DORIS systems in detail.The data processing of GNSS,ocean altimetry and DORIS mainly studied the carrier phase smoothing pseudorange algorithm,data denoising and the method of converting relative ionospheric total electron content(TEC)to absolute TEC,respectively.Secondly,this contribution develops a dual-system GPS/GLONASSS global ionosphere model,and generate correspondingly ionospheric products,including spherical harmonic coefficient files,global ionosphere TEC maps and DCB files.Additionally,the accuracy of those products generated is compared with the products of GPS single system and various ionosphere associate analysis centers(IAACs).Results illustrate that the GPS/GLONASSS dual system products have good consistency with IAACs products,and the accuracy of the GPS single system product is improved to a certain extent,but the improvement is limited.It is necessary to further integrate the space-based data to improve the performance of the ionosphere model in the ocean and away from GNSS reference stations.Lastly,this study integrates GPS/GLONASS,satellite altimetry and DORIS data to develop a high-precision multi-source global ionospheric model.To solve the problem of systematic bias of observations among different systems,the weights are precisely determined utilizing Helmert variance components estimation.In order to demonstrate the accuracy and reliability of the model constructed by multi-source data fusion,the GIMs from individual IAACs,GPS/GLONASS GIMs,dSTEC observations and GIMs under different geomagnetic activities was used in this part.In addition,this paper also displays the mean bias of each space-based system relative to the ground-based GNSS.