Possibilities and problems of the inerpretation of solar magnetograph measurements and applications to flare-active regions

Solar photoelectric magnetographs measure the state of polarization in magnetosensitive spectrum lines. The derivation of magnetic field parameters from such data requires a 'calibration' in terms of a transfer theory for polarized radiation, therefore it depends on model assumptions. The primary polarimetric measurements are influenced by disturbances introduced within the telescope and in the atmosphere of the Earth. We review the basic uncertainties encountered in the interpretation of magnetograph data, but also possibilities for deriving more reliable information. The problems are illustrated by describing the data handling of the Potsdam vector magnetograph in more detail, moreover, examples of observed flare- active regions demonstrate the state of information which nowadays can be obtained. (author). 21 refs.; 3 figs