Polarization dependence of radiowave propagation through Antarctic ice

TL;DR

This study investigates how radio wave propagation through Antarctic ice depends on polarization, revealing amplitude variations but no birefringent time delays, thus informing ice property models relevant for radio-based ice measurements.

Contribution

It provides the first polarization-dependent measurements of radio wave reflections at the South Pole, testing birefringence effects predicted by ice crystal orientation models.

Findings

Amplitude varies with polarization angle.

No birefringent time-delay detected at 0.1‰ level.

Supports models with minimal birefringent asymmetry.

Abstract

Using a bistatic radar system on the ice surface, we have studied radiofrequency reflections off internal layers in Antarctic ice at the South Pole. In our measurement, the total propagation time of ~ns-duration, vertically broadcast radio signals, as a function of polarization axis in the horizontal plane, provides a direct probe of the geometry-dependence of the ice permittivity to depths of 1--2 km. Previous studies in East Antarctica have interpreted the measured azimuthal dependence of reflected signals as evidence for birefringent-induced interference effects, which are proposed to result from preferred alignment of the crystal orientation fabric (COF) axis. To the extent that COF alignment results from the bulk flow of ice across the Antarctic continent, we would expect a measurable birefringent asymmetry at South Pole, as well. Although we also observe clear dependence of reflected amplitude on polarization angle in our measurements, we do not observe direct evidence for birefringent-induced time-delay effects at the level of 0.1 parts per mille.