Joint establishment of the geomagnetic model for mainland China based on CHAMP satellite and surface vector data

We firstly made a pre-processing to vector data of magnetism from surface observational stations and CHAMP satellite, along with newest 12 Chinese Meridian Project observations; then put all data into a specific time point by the 12th generation International Reference Field (IGRF12) model. Moreover, the external fields that include the main field, ionospheric field, magnetospheric field, their induced field, and the weak toroidal magnetic field were respectively removed by IGRF12 and the 4th generation Comprehensive Model (CM4) models. Finally, the China lithospheric field (elements X, Y, Z and F) model (SCH2000) was created by the spherical cap harmonic model, and the China geomagnetic field (CGRF2000) was created by IGRF12. During the modeling process, the effects from the altitude term, the selection of truncation level and the control of boundary were seriously considered. In terms of comparison of the Root-Mean-Square (RMS) error and so on, the SCH2000 with degree 8 was thought to be an ideal joint model to describe the lithospheric field over China, which were also compared with models like SCH1936, CM4 and Taylor polynomial. We found that their results, to some degrees, are consistent.. In view of location and intensity, SCH2000 reflects the lithospheric field more precisely compared to other regional models. Some differences between SCH2000 and CM4 mainly result from the measuring data and truncation level. Comparison shows the variations with altitudes are close between SCH2000 and CM4. As for the distributions of magnetic fields, there is also a good consistence between CGRF2000 and IGRF12 models.