  Glacial ice is used as a target material for the detection of ultra-high
energy neutrinos, by measuring the radio signals that are emitted when those
neutrinos interact in the ice. Thanks to the large attenuation length at radio
frequencies, these signals can be detected over distances of several
kilometers. One experiment taking advantage of this is the Radio Neutrino
Observatory Greenland (RNO-G), currently under construction at Summit Station,
near the apex of the Greenland ice sheet. These experiments require a thorough
understanding of the dielectric properties of ice at radio frequencies. Towards
this goal, calibration campaigns have been undertaken at Summit, during which
we recorded radio reflections off internal layers in the ice sheet. Using data
from the nearby GISP2 and GRIP ice cores, we show that these reflectors can be
associated with features in the ice conductivity profiles; we use this
connection to determine the index of refraction of the bulk ice as n=1.778 +/-
0.006.
