Calibration of a full-disc longitudinal magnetogram at the Huairou Solar Observing Station

Abstract

Based on a spectral profile analysis of a filter magnetograph and the application of the astronomical data analysis technique, a full‐disc distribution of Stokes I‐to‐V crosstalk in the solar magnetism and activity telescope (SMAT) has been acquired quantitatively. We produce a correction template to remove the full‐disc Stokes I‐to‐V crosstalk. This template is important for the accuracy of the full‐disc longitudinal magnetogram. Then, we propose an observational calibration method under the weak‐field approximation on the basis of the scanning spectrum of the filter magnetograph. The following main results have been obtained. (i) For the original Stokes V images, there is about −1.67 × 10−3 of Stokes I crosstalk into V at all wavelength positions, and this crosstalk presents itself as a horse‐saddle surface distribution on the full disc. (ii) A sample of the calibration curve at different wavelength positions is given. (iii) After being calibrated into magnetic flux density, the Stokes I‐to‐V crosstalk has an amplitude of about 50 G, but introduces negative and positive spurious magnetic fields into the blue and red wing magnetograms, respectively.

From polarimetry to helicity: Studies of solar magnetic fields at the Huairou Solar Observing Station

“…It is found a relative high correlation between both vector magnetogams observed from SMFT and SMAT. The study on the spatial integration scanning spectra of filter magnetograph is also important for the calibration of the fulldisk vector magnetic fields, which was made by Wang et al (2010) [33]. It is believed that solar active phenomena often relate to the complex configurations of coronal and chromospheric magnetic fields.…”