The Effects of Polarization Crosstalk and Solar Rotation on Measuring Full‐Disk Solar Photospheric Vector Magnetic Fields

Abstract

Observations of full-disk solar photospheric vector magnetic fields are very important for the studies of the global properties and evolution of solar magnetism. Such observations can allow us to investigate the magnetic connectivities between active regions and the nonpotentiality of magnetic fields with a much wider field of view (FOV) than do local-region observations. Therefore, we developed a full-disk vector magnetograph for the Solar Magnetism and Activity Telescope (SMAT) at Huairou Solar Observing Station. In this paper, we point out two problems that affect measurement accuracy of full-disk vector magnetic fields: circular-to-linear polarization crosstalk produced by the instrument, and wavelength shift due to solar rotation. An attempt is made to correct such polarization crosstalk and to reconstruct full-disk vector magnetic fields from polarization data. We also give a superficial discussion about the problem of an incompletely wide field of view (IWFOV) of the Lyot filter in the measurements of full-disk solar vector magnetic fields. In addition, the polarization data of the SMAT are compared with those of the Solar Magnetic Field Telescope (SMFT), which operates the local-region observations. Although the SMFT is 2-3 times as sensitive as the SMAT, there is a basic agreement on the polarization data of the two instruments.