In situ estimation of ice crystal properties at the South Pole using LED calibration data from the IceCube Neutrino Observatory

The IceCube Neutrino Observatory instruments
about 1 km3 of deep, glacial ice at the geographic South
Pole. It uses 5160 photomultipliers to detect Cherenkov
light emitted by charged relativistic particles. An unexpected
light propagation effect observed by the experiment is an
anisotropic attenuation, which is aligned with the local flow
direction of the ice. We examine birefringent light propaga-
tion through the polycrystalline ice microstructure as a pos-
sible explanation for this effect. The predictions of a first-
principles model developed for this purpose, in particular
curved light trajectories resulting from asymmetric diffusion,
provide a qualitatively good match to the main features of the
data. This in turn allows us to deduce ice crystal properties.
Since the wavelength of the detected light is short compared
to the crystal size, these crystal properties include not only
the crystal orientation fabric, but also the average crystal size
and shape, as a function of depth. By adding small empiri-
cal corrections to this first-principles model, a quantitatively
accurate description of the optical properties of the IceCube
... mehr
glacial ice is obtained. In this paper, we present the exper-
imental signature of ice optical anisotropy observed in Ice-
Cube light-emitting diode (LED) calibration data, the theory
and parameterization of the birefringence effect, the fitting
procedures of these parameterizations to experimental data,
and the inferred crystal properties