In-situ Measurements of Ice Properties for the Radar Echo Telescope for Cosmic Rays

The upper 20 meters of the polar ice sheets exhibit significant density inhomogeneity. Understanding these ice effects on radio signal propagation is crucial for radio-based ultra-high-energy neutrino searches that use ice as a detection medium. We present in-situ measurements of density ($\rho$) and refractive index ($n$) in the upper 13 meters of ice at the Radar Echo Telescope for Cosmic Rays (RET-CR) site near Summit Station on the Greenland ice sheet, taken during the summer of 2024. The density was measured by assessing the mass and volume of extracted ice cores. The resulting $\rho$ and $n$ profiles are consistent with previous measurements at Summit. Additionally, a frequency-modulated continuous-wave signal was broadcast from an in-ice transmitter and measured at various depths inside a borehole. These signals were compared with simulations solving Maxwell's equations on a grid, using ice models derived from the in-situ $\rho$ and $n$ measurements.