Polarimetric radar measurements for the characterization of ice crystal orientation fabric and anisotropic rheology within Rutford Ice Stream, 2016/2017 to 2019/2020

A ground-based radar survey consisting of 35 discrete quad-polarization measurement sites over three field seasons was undertaken on Rutford Ice Stream, West Antarctica. Sites A01 to A10 were collected on 20 January 2017, along a profile orientated perpendicular to the ice flow direction. The 10 sites are located between the central ice flowline and the ice-stream margin along a profile of length 8.5 km with the inter-site spacing decreasing toward the ice-stream margin. Sites B01 to B10 were collected on 05 December 2019, along a profile orientated parallel to the central flowline. The sites were surveyed with the first site 4 km upstream of site A01 and the inter-site distance spacing fixed at 4 km. Sites C01 to C11 were collected on 14 December 2018, and located between sites A01 and A02 at 200 m spacing. Sites D01-D04, collected on 25 January 2019, are downstream of A01 and form a diamond shape with 800 m spacing. At each site, polarimetric radar-sounding measurements were made using an autonomous phase-sensitive radio-echo sounder (ApRES), a frequency-modulated continuous-wave radar. The ApRES has a centre frequency of 300 MHz and a bandwidth of 200 MHz, which results in a range resolution of approximately 40 cm in ice. ApRES radar data were collected as part of the BEAMISH Project (NERC AFI award numbers NE/G014159/1 and NE/G013187/1).

Polarimetric data were acquired in the quad-polarimetric manner as described in Young et al. (2021) but following the antenna layout and rotation scheme presented in apres-quadpol-field-rutford.jpg. The white open-structure (skeleton-slot) antennas were placed 8 m apart at their outside edge, aligned to magnetic North (40 deg E at the time of acquisition), with the transmit antenna at the northern end. For the initial measurements, antenna connectors are aligned pointing towards magnetic East (polarization termed VV). Five measurements were taken at each site, rotating one antenna at a time through 90 deg anti-clockwise (counter-clockwise) around its centre, starting with the transmit antenna. This results in a sequence of five measurements VV-HV-HH-VH-VV with the final VV (termed VV-rotated) in the opposite orientation to the initial VV. Alignment of the flags used to locate and orientate the antennas was done with a magnetic compass with uncertainty of +/- 5 deg. The raw field data are made available here. No data processing has been applied.

Data quality allows for analysis of anisotropy within the upper half of the ice column (approximately 1000 m depth).

Radar: ApRES (British Antarctic Survey's Autonomous phase-sensitive Radio-Echo Sounder) - operated with a linear up-chirp from 200 to 400 MHz over the course of 1 s. An ensemble (burst) of 100 chirps was recorded for each polarimetric measurement.