  The Full-disk magnetograph is a main scientific payload onboard the Advanced
Space based Solar Observatory (ASO-S/FMG) that through Stokes parameter
observation to measures the vector magnetic field. The accuracy of
magnetic-field values is an important aspect of checking the quality of the FMG
magnetic-field measurement. According to the design of the FMG, the linear
calibration method under the weak-field approximation is the preferred scheme
for magnetic-field calibration. However, the spacecraft orbital velocity can
affect the position of observed spectral lines, then result in a change of the
polarization-signal strength. Thus, the magnetic field is modulated by the
orbit velocity of the spacecraft. In this article, through cross calibration
between FMG and HMI (Helioseismic and Magnetic Imager onboard the Solar Dynamic
Observatory), the effects of spacecraft orbital velocity on the coefficient of
magnetic-field calibration are investigated. By comparing the magnetic field of
FMG and HMI with spacecraft orbital velocity as an auxiliary reference, the
revised linear-calibration coefficients that depend on spacecraft orbital
velocity are obtained. Magnetic field of FMG corrected by the revised
calibration coefficients removing the effect of spacecraft orbital velocity
will be more accurate and suitable for scientific research.
