Comparison of Line-of-Sight Magnetic Field Observed by ASO-S/FMG, SDO/HMI and HSOS/SMAT

The Full-disk MagnetoGraph (FMG) onboard the Advanced Space based Solar Observatory has obtained a series of line-of-sight magnetic-field measurements since its launch in October 2022. It is important to compare its observational data with other existing solar telescopes. In this paper, we make a detailed comparison of four active regions and a pore region simultaneously observed by FMG, the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamic Observatory, and the Solar Magnetism and Activity Telescope (SMAT) at Huairou Solar Observing Station. We find that the magnetic-field structure and spatial distribution are basically consistent among these three instruments. The initial correlation coefficient of magnetic field is approximately 0.90. The coefficient slightly increases when sunspot umbra regions are excluded, and it increases significantly up to 0.98 for the magnetic field in penumbra regions. The magnetic field observed by FMG tends to be weaker than the HMI in strength in sunspot umbra due to saturation effect, whereas larger outside sunspot. The differences are probably due to different noise levels, seeing conditions (SMAT is affected by the Earth’s atmosphere) and observational and calibration methods.