基于CHAMP卫星与地面矢量数据联合建立中国地磁模型

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

首先对地面台站以及CHAMP卫星的矢量磁测数据进行预处理,结合12个子午工程台站最新的磁测数据,并利用第十二代国际地磁参考场模型(IGRF12)对不同数据归算至统一时间点,再结合第四代地磁场综合模型(CM4)计算并移除主磁场、磁层磁场、电离层磁场、感应磁场及较为微弱的环形场,最后通过球冠谐(SCH)模型联合建立了中国地区岩石圈磁场(地磁要素X、Y、Z和总强度F)的球冠谐模型(SCH2000),结合IGRF12得到了中国地磁模型(CGRF2000).建模同时考虑了测点数据海拔高度的影响,并讨论了截断阶数的选取以及边界效应的控制问题.通过比较均方偏差(RMS),认为8阶SCH2000模型可较好地反映中国地区岩石圈磁场,其分布与SCH1936、CM4以及Taylor多项式模型具有一定的相似性.从位置和强度来看,SCH2000模型所反映的岩石圈磁场更为准确,而与CM4存在一定差异,除了测点不同,截断阶数也是原因之一.通过验证,SCH2000模型各要素随高度的变化与CM4模型较为一致,所建立的CGRF2000与IGRF12模型的分布也较为相似.

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.