  We discuss spectropolarimetric measurements of photospheric (Fe I 630.25 nm)
and chromospheric (Ca II 854.21 nm) spectral lines. Our long-term goal is to
diagnose properties of the magnetic field near the base of the corona. We
compare ground-based two-dimensional spectropolarimetric measurements with
(almost) simultaneous space-based slit spectropolarimetry. The ground-based
observations were obtained May 20, 2008, with IBIS in spectropolarimetric mode,
The space observations were obtained with the Spectro-Polarimeter aboard the
HINODE satellite. The agreement between the near-simultaneous co-spatial IBIS
and HINODE Stokes-V profiles at 630.25 nm is excellent, with V/I amplitudes
compatible with to within 1 %. IBIS QU measurements are affected by residual
crosstalk from V, arising from calibration inaccuracies, not from any inherent
limitation of imaging spectroscopy. We use a PCA analysis to quantify the
detected cross talk. Chromospheric magnetic fields are difficult to constrain
by polarization of Ca II lines alone. However, we demonstrate that high
cadence, high angular resolution monochromatic images of fibrils in Ca II and
H-alpha, can be used to improve the magnetic field constraints, under
conditions of high electrical conductivity. Such work is possible only with
time series datasets from two-dimensional spectroscopic instruments under
conditions of good seeing.
