Radiofrequency Ice Dielectric Measurements at Summit Station, Greenland

TL;DR

This study measures radio-frequency attenuation and internal layer reflections in Greenland ice, revealing that ice is largely coherent, non-dispersive, and exhibits minimal birefringence, which is valuable for neutrino detection.

Contribution

It provides new measurements of ice dielectric properties at Summit Station, including reflection coefficients, birefringence, and dispersion limits, enhancing understanding for neutrino detection applications.

Findings

Reflected signals are consistent with being entirely coherent up to 1500 m depth.

Internal layer reflection coefficients are approximately -60 to -70 dB.

Birefringent effects are smaller than those observed at South Pole.

Abstract

We recently reported on the radio-frequency attenuation length of cold polar ice at Summit Station, Greenland, based on bistatic radar measurements of radio-frequency bedrock echo strengths taken during the summer of 2021. Those data also include echoes attributed to stratified impurities or dielectric discontinuities within the ice sheet (layers), which allow studies of a) estimation of the relative contribution of coherent (discrete layers, e.g.) vs. incoherent (bulk volumetric, e.g.) scattering, b) the magnitude of internal layer reflection coefficients, c) limits on the azimuthal asymmetry of reflections (birefringence), and d) limits on signal dispersion in-ice over a bandwidth of ~100 MHz. We find that i) after averaging 10000 echo triggers, reflected signal observable over the thermal floor (to depths of approximately 1500 m) are consistent with being entirely coherent, ii) internal layer reflection coefficients are measured at approximately -60 to -70 dB, iii) birefringent effects for vertically propagating signals are smaller by an order of magnitude relative to comparable studies performed at South Pole, and iv) within our experimental limits, glacial ice is non-dispersive over the frequency band relevant for neutrino detection experiments.