  The advancement of our understanding of MHD turbulence opens ways to develop
new techniques to probe magnetic fields. In MHD turbulence, the velocity
gradients are expected to be perpendicular to magnetic fields and this fact was
used by Gonsalvez-Casanova & Lazarian to introduce a new technique to trace
magnetic fields using velocity centroid gradients. The latter can be obtained
from spectroscopic observations. We apply the technique to GALFA HI survey data
and compare the directions of magnetic fields obtained with our technique with
the direction of magnetic fields obtained using PLANCK polarization. We find
excellent correspondence between the two ways of magnetic field tracing, which
is obvious via visual comparison and through measuring of the statistics of
magnetic field fluctuations obtained with the polarization data and our
technique. This suggests that the velocity centroid gradients can provide a
reliable way of measuring of the foreground magnetic field fluctuations and
thus provide a new way of separating foreground and CMB polarization signals.
