Several problems in measuring solar vector magnetic fields

Observations of solar photosphere vector magnetic fields with a magnetograph are subjected to many difficulties, such as azimuth ambiguity, magnetic saturation, Faraday rotation, scattered light, polarization crosstalk, and wavelength shift, and so on. Among these issues, Faraday rotation and scattered light are obvious in local-region vector magnetic field measurements with the 35 cm Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station (HSOS), while polarization crosstalk and wavelength shift are obvious in full-disk vector magnetic field measurements made with a new-developed telescope named Solar Magnetism and Activity Telescope (SMAT). In this paper we put emphasis on these four issues to show how they could affect the measurement accuracy of solar vector magnetic fields. Some preliminary attempts are also made to overcome them.