Study of the geomagnetic field’s regional gradients in Chinese continent using three-dimensional surface Spline model

We combined domestic ground-based and satellite magnetic measurements to create a regional three-dimensional surface Spline (3DSS) gradient model of the main geomagnetic field over the Chinese continent. To improve the precision of the model, we considered the data gap between the ground and satellite data. We compared and analyzed the results of the Taylor polynomial, surface Spline, and CHAOS-6 (the CHAMP, Ørsted and SAC-C model of Earth’s magnetic field) gradient models. Results showed that the gradients in the south−north and east−west directions of the four models were consistent. The 3DSS model was able to express not only gradients at different altitudes, but also average gradients inside the research area. The two Spline models were able to capture more information on gradient anomalies than were the fitted models. Strong local anomalies were observed in northern Xinjiang, Beijing, and the junction area between Jiangsu and Zhejiang, and the total intensity F decreased whereas the altitude increased. The gradient decreased by 21.69% in the south−north direction and increased by 11.78% in the east−west direction. In addition, the altitude gradient turned from negative to positive while the altitude increased. The Spline model and the two fitted models differed mainly in the field sources they expressed and the modeling theory.