Evaluating data quality and reference instrument robustness: insights of 12 years DI magnetometer comparisons in the Geomagnetic Network of China

Abstract. Statical analyses were conducted in sequence on 12 sets of geomagnetic instrument comparison data from the Chinese Geomagnetic Network (GNC) between 2010 and 2024. First, by examining these comparison data, it was found that when their cumulative probabilities at the same level, the instrument differences for declination (D) are significantly higher than those for inclination (I). For the same set of instruments, as the frequency of observer changes increases, the instrument differences for D increase, while no significant change was observed for I. This indicates that inter-observer differences have a notable impact on D, primarily due to the complexity of aligning the azimuth marks and levelling instruments. Second, though a multi-source error uncertainty analysis, including instrument error, operator related error, pillar correction error and so on, the systematic differences between the reference fluxgate theodolite and the test instruments were quantified. The operator related errors of D and I were successfully separated and consistent with the observed experimental results, confirming that operator related error is the primary factor contributing to instrument differences. The analysis also validated the high stability and reliability of the reference instrument. The former finding can serve as an assessment criterion for network-level numerical quality, while the latter can be used to verify the long-term stability of the reference instrument.