The GRACE-FO mission is a dedicated gravity field mission. Since the satellites carry two fluxgate magnetometers each, these have been calibrated and characterized for pertubations. The standard deviation of geomagnetic quiet time residual with high-performance geomagnetic field model (CHAOS7) is below 10 nT.
A detailed study has been published here:
Stolle, C., Michaelis, I., Xiong, C. et al. Observing Earth’s magnetic environment with the GRACE-FO mission. Earth Planets Space 73, 51 (2021). https://doi.org/10.1186/s40623-021-01364-w
The data has been published here:
Michaelis, Ingo; Stolle, Claudia; Rother, Martin (2021): GRACE-FO calibrated and characterized magnetometer data. V. 0201. GFZ Data Services. https://doi.org/10.5880/GFZ.2.3.2021.002
A new study using Machine Learning methods has been published here:
K. Styp-Rekowski, C. Stolle, I. Michaelis and O. Kao, "Calibration of the GRACE-FO Satellite Platform Magnetometers and Co-Estimation of Intrinsic Time Shift in Data," 2021 IEEE International Conference on Big Data (Big Data), 2021, pp. 5283-5290, doi: 10.1109/BigData52589.2021.9671977.