  We report on our studies of the physical structure of the planetary nebula
(PN) NGC7662. Using (3D) Integral Field Spectroscopy we have been able to
measure the electron temperature more accurately and at a larger number of
radial locations than before. Here we briefly present our method by which we
find a strong positive temperature gradient with increasing radius. According
to hydrodynamic models a hot halo, when compared to the central star, can be
the product of the passage of an ionization front (e.g. Marten 1993). Such a
gradient is not found in equilibrium models, and this finding - when confirmed
for other objects - strongly advocates the use of hydrodynamic models when
modeling PN halos.
