  IceCube is a neutrino observatory at Earth's South Pole that uses glacial ice
as detector medium. Secondary particles from neutrino interactions produce
Cherenkov light, which is detected by an array of photo detectors deployed
within the ice. In distinction from the glacial bulk ice, hole ice is the
refrozen water in the drill holes around the detector modules, and is expected
to have different optical properties than the bulk ice. Aiming to improve
detector precision, this study presents a new method to simulate the
propagation of light through the hole ice, introducing several new calibration
parameters. The validity of the method is supported by a series of statistical
cross checks, and by comparison to measurement and simulation results from
other calibration studies. Evaluating calibration data indicates a strongly
asymmetric shielding of the detector modules. A preliminary analysis suggests
that this cannot be accounted for by the shadow of cables, but can be explained
by hole ice with a suitable scattering length, size, and position relative to
the detector modules. The hole-ice approximation, which is used in the standard
simulation chain is found to disagree with all existing direct-propagation
methods and should be recalculated with a new direct-simulation run.
