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Abstract The Radio Neutrino Observatory-Greenland (RNO-G, at Summit Station) experiment comprises an extensive fat-dipole antenna array deployed into ice boreholes over an eventual area of approximately 35 km². Since the RNO-G experimental sensitivity depends on the radio-frequency properties of the firn, which are known to vary laterally on sub-km distance scales and vertically on sub-meter distance scales, a technique for quickly extracting information on firn ice properties with depth ($$n(z)$$) during drilling and deployment is desirable. Given that a dipole’s resonant wavelength is fixed by geometry, the resonant frequency$$f_{res}$$(measured as an S-parameter reflection coefficient [‘$$S_{11}$$’] minimum) scales inversely with the local refractive index, allowing a translation of a depth-dependent$$S_{11}$$(z) profile into$$n(z)$$.$$S_{11}$$(z) data were initially taken in August 2024 using a dipole lowered into a newly drilled 98 ± 1 mm diameter, 350 m deep borehole at Summit Station, Greenland, approximately 1 km from the site of the original GISP-2 core; improved measurements were subsequently made in May 2025. We conclude that$$S_{11}$$(z) data can be used to estimate$$n(z)$$, on 50 cm vertical scales, at the per cent level of accuracy required by experiments such as RN0-G. 

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.