A Study on Correcting the Effect of Polarization Crosstalk in Full-Disk Solar Photospheric Magnetic Field Observations

Abstract

Magnetography using magnetic sensitive lines is regarded traditionally as the main instrument for measuring the magnetic field of the whole Sun. Full polarized Stokes parameters (\(I\), \(Q\), \(U\), \(V\)) can be used to deduce the magnetic field under specific theoretical models or inversion algorithms. Due to various reasons, there are often cross-talk effects among Stokes signals observed directly by magnetographs. Especially, the circularly polarized signal \(V\) usually seriously affects the linearly polarized \(Q\) and \(U\) signals, which is one of the main errors in the value of the transverse magnetic field (parallel to the solar surface) that is related to \(Q\) and \(U\). The full-disk magnetograph onboard the Advanced Space based Solar Observatory (ASO-S/FMG) is designed to observe Stokes parameters and deduce the magnetic-field vector. In this article, the methods for correcting the effects of cross-talk \(V\) on \(Q\) and \(U\) based on the assumption of perfectly symmetric \(Q\) and \(U\) and anti-symmetric Stokes \(V\) profiles and a new method for reducing the crosstalk effect under observation mode of the FMG are developed. Through the test, it is found that the two methods are effective in cross-talk removal in the sunspot region and have better consistency. Additionally, the developed method can be applied to remove the cross-talk effect by using only one group of \(Q\), \(U\) and \(V\) images observed at one wavelength position.