Geomagnetic field data has been widely used in fields such as geophysical exploration in the past. In recent years, its application in the navigation area has received increasing attention, and geomagnetic navigation has become a research hotspot in the current navigation field. The accuracy of geomagnetic field data has a significant impact on navigation accuracy. One of the important applications of the World Magnetic Model （WMM） is to serve the aircraft navigation. This paper attempts to utilize the measured aeromagnetic data from the Weishui region of Shaanxi Province in western China and the Yuyao region of Zhejiang Province in eastern China to study and analyze the deviations between them and the WMM2020 and WMM2025 model data. This would provide valuable references for correcting model data and achieving high-precision navigation for aircraft.

In this study, we conducted an aeromagnetic survey in an area spanning 2 km×3 km （horizontal×vertical） with a grid size of 100 m×7 m （horizontal×vertical）. Using an unmanned aerial vehicle （UAV） at an altitude of 120 m, geomagnetic data are collected from 14 survey lines, totaling 36674 aeromagnetic points. Within the aeromagnetic survey area, a geomagnetic diurnal variation observation station was set up to correct the diurnal variation effect on the measured aeromagnetic data. This paper systematically analyzes the differences between the diurnally corrected measured geomagnetic field data and the north, east, and down components of the WMM2020 model data. The results reveal significant differences in the north and vertical components between the WMM2020 model and the measured aeromagnetic data in the Weishui region of Shaanxi Province, while the differences in the Yuyao region of Zhejiang Province are relatively small. The differences in the north and vertical components between the WMM2020 model data and the aeromagnetic data in the Yuyao region are around 48 nT, while those in the Weishui region are around 130 nT. In both regions, the differences in the east component between the model data and the aeromagnetic data are very small. Through overall correction of the WMM2020 model data, the mean absolute error （MAE） of the north and vertical components between the model data and the measured data in the Yuyao region decreased to around 20 nT, representing a reduction of about 60%, and the root mean squared error （RMSE） decreased to around 23 nT, representing a reduction of about 56%. In the Weishui region, the MAE of the north and vertical components decreased to around 30 nT, with a reduction of 76% in both MAE values, and the RMSE decreased to around 40 nT, representing a reduction of about 69%. It is clear that after correction of model data, the WMM2020 model data become more closely aligned with the measured geomagnetic data in the local regions. The deviations are significantly reduced.

The study also found that the characteristics of geomagnetic field variations in these two regions are significantly different. The variations in the three components of the geomagnetic field in the Weishui region are more complex than those in the Yuyao region, which may be related to the differences in geological structures. Compared with the Yuyao region, the geological structure of the Weishui region is more complex. The underground of the Weishui region contains various energy minerals such as coal, natural gas, and geothermal energy, as well as various metal minerals such as copper, gold, lead, and zinc. However, the underground minerals in the Yuyao region are mainly non-metallic fluorite deposits.

The total geomagnetic field intensity in the Weishui region is significantly greater than that in the Yuyao region. The variation range of the total intensity in the Weishui region is between 52500 nT and 52800 nT, with a variation amplitude of 300 nT. The variation of the total intensity in the Yuyao region ranges from 48600 nT to 48800 nT, with a variation amplitude of 200 nT. It can be seen that the fluctuation of the total intensity in the Weishui region is greater than that in the Yuyao region. The mean values of the north and east components of the measured aeromagnetic data in the Yuyao region are approximately 2200 nT and 1300 nT larger, respectively, than those in the Weishui region. However, the mean value of the vertical component in the Yuyao region is approximately 7200 nT, lower than that in the Weishui region.

In addition, this paper also compares the differences between measured data, WMM2020 model data, and WMM2025 model data. The result reveals that the deviation between measured data and WMM2020 model data in the Weishui region is smaller than that between measured data and WMM2025 model data. However, the situation is reversed in the Yuyao region, where the deviation between measured data and WMM2020 model data is larger than that between measured data and WMM2025 model data. This indicates that after the WMM model is updated from the version of WMM2020 to the version of WMM2025, the accuracy of model data has been improved in some regions, while it may not have been improved in other regions. Analysis and processing of geomagnetic data should be conducted carefully when the updated model data are used.