A Study on Correcting Magnetic Field Calibration Coefficients in Full-Disk Magnetograph onboard the Advanced Space based Solar Observatory (ASO-S/FMG)

Full-disk magnetograph is a main scientific payload onboard the Advanced Space based Solar Observatory (ASO-S/FMG) that through Stockes parameters observation to measure the vector magnetic field. The accuracy of magnetic field values is an important aspect of checking the quality of FMG magnetic field measurement. According to the design of FMG, the linear calibration method under weak field approximation is the preferred scheme for magnetic field calibration. However, the satellite orbit velocity with longitudinal component can affect the position of observed spectral lines, then result in the change of polarization signals strength. Thus, the magnetic field is modulated by the orbit velocity of satellite. In this paper, through cross calibration betweeen %FMG and SMAT (Solar Magnetism and Activity Telescope at Huairou Solar Observing Station), FMG and HMI (Helioseismic and Magnetic Imager onboard Solar Dynamic Observatory), the effects of satellite orbital velocity on the coefficient of magnetic field calibration are investigated. By comparions magnetic field of FMG and HMI %, FMG and SMAT with satellite orbital velocity as auxiliary reference, the revised linear calibration coefficients that depend on satellite orbital velocity are obtained. Magnetic field of FMG corrected by revised calibration coefficients avoiding the effect of satellite orbital velocity would be more accurate and suitable for scientific research.