  We develop a new ''core field structure'' (CFS) model to predict the magnetic
field strength and magnetic field fluctuation profile of dense cores using gas
kinematics. We use spatially resolved observations of the nonthermal velocity
dispersion from the Green Bank Ammonia survey along with column density maps
from SCUBA-2 to estimate the magnetic field strength across seven dense cores
located in the L1688 region of Ophiuchus. The CFS model predicts the profile of
the relative field fluctuation, which is related to the observable dispersion
in direction of the polarization vectors. Within the context of our model we
find that all the cores have a transcritical mass-to-flux ratio.
