Large-Scale Solar Magnetic Fields Observed with the Infrared Spectro-Polarimeter IRmag at the National Astronomical Observatory of Japan: Comparison of Measurements Made in Different Spectral Lines and Observatories

This study presents the results of a quantitative analysis of IRmag (infrared Stokes spectro-polarimeter, National Astronomical Observatory of Japan, (NAOJ)/Mitaka) observations in three spectral lines Fe I 1564.8 nm, Si I 1082.72 nm, He I 1083.0 nm, and comparison between IRmag magnetograms and ones from the Solar Dynamic Observatory/Helioseismic and Magnetic Imager (SDO/HMI), Global Oscillation Network Group (GONG), Wilcox Solar Observatory (WSO), and Solar Telescope for Operative Predictions (STOP). It is shown that there is a good correlation between observations in all three IRmag spectral lines, but with significant differences in the measured field strengths caused by different depths of formation and, probably, by calibration issues. The correlation of IRmag magnetograms with ones from other observatories, and between different observatories among each other, is as good as 0.70 - 0.95, depending on the combination, but nevertheless there are significant systematic differences (linear-regression coefficients deviating from unity) between different data sets (up to a factor of three or even more).