SDO/HMI Vector Magnetic Field

The vector magnetic field is derived from full-disk filtergrams collected in a 135-second sequence. (90 seconds after 13 April 2016). The observations are obtained in polarized light at several wavelengths across a spectral line. The filtergrams are calibrated and registered to account for solar rotation before being combined to provide Stokes polarization parameters. The parameters are used to determine the magnetic and other plasma parameters using VFISV, a Milne-Eddington inversion code. The final step is to disambiguate the data, that is to infer the azimuthal direction of the transverse field.