Antarctic Radio Frequency Albedo and Implications for Cosmic Ray Reconstruction

TL;DR

This study measures the RF signal reflection coefficients at the Antarctic ice surface using ANITA data, aiding in cosmic ray and neutrino energy estimations by comparing observed and expected reflection based on Fresnel equations.

Contribution

It provides the first direct measurements of RF reflection coefficients at the Antarctic ice surface, validating Fresnel equation predictions for cosmic ray and neutrino detection.

Findings

Reflection coefficients are consistent with Fresnel equations.

Horizontal and vertical polarizations show expected differences.

Results improve energy reconstruction accuracy for cosmic rays and neutrinos.

Abstract

From an elevation of ~38 km, the balloon-borne ANtarctic Impulsive Transient Antenna (ANITA) is designed to detect the up-coming radio frequency (RF) signal resulting from a sub-surface neutrino-nucleon collision. Although no neutrinos have been discovered thus far, ANITA is nevertheless the only experiment to self-trigger on radio frequency emissions from cosmic-ray induced atmospheric air showers. In the majority of those cases, down-coming RF signals are observed via their reflection from the Antarctic ice sheet and back up to the ANITA interferometer. Estimating the energy scale of the incident cosmic rays therefore requires an estimate of the fractional power reflected at the air-ice interface. Similarly, inferring the energy of neutrinos interacting in-ice from observations of the upwards-directed signal refracting out to ANITA also requires consideration of signal coherence across the interface. By comparing the direct Solar RF signal intensity measured with ANITA to the surface-reflected Solar signal intensity, as a function of incident elevation angle relative to the surface {\Theta}, we estimate the power reflection coefficients R({\Theta}). We find general consistency between our average measurements and the values of R({\Theta}) expected from the Fresnel equations, separately for horizontal- vs. vertical-polarizations.