On the removal of the sign ambiguity in the photospheric transverse magnetic field

We present a method for removing the ambiguity in the transverse component of the photospheric magnetic field measured by vector magnetographs. The me thod is based upon the use of the divergence-free condition satisfied by th e magnetic field in the sense of least squares. The method requires the mea surement of the longitudinal component of the magnetic field at two depth l evels in the photosphere. The method is is shown to be efficient when compa red to other existing methods on some particular analytical force-free magn etic fields.