Best practices for collecting polarimetric data with ApRES for constraining ice-fabric orientation and its spatial variability

In recent years radar polarimetry has re-surfaced as an ideal tool to determine ice-fabric patterns and linked mechanical ice anisotropy. The leap forward was facilitated by coherent data processing often collected by phase-sensitive Radio-Echo-Sounding (pRES) systems at fixed locations. The polarimetric response can either be synthesized from a set of quad-polarimetric measurements or obtained by manually rotating the antennas. Specifics of the data collection in the field varied between the different surveys, and no set of best practices has yet emerged.  Here we present a systematic study that includes more than fifty different combinations of how polarimetric data can be acquired, including:

• different distances between the transmitter and receiver (2, 4 and 8 m)
• different combinations in polarization orientation (22.5 deg)
• a comparison between discrete full azimuthal data collected every 22.5 degrees and synthesized data collected in a quad-pole setup
• the effect of 180-degree polarization orientation on repeat measurements, e.g., basal melt rate and polarimetric analysis, e.g., coherence phase
• definition of Horizontal (H) and Vertical (V) orientation is pRES antenna setup and its impact on synthesizing and analyzing data
• 90-degree fabric orientation ambiguity in polarimetric data

This study aims to provide best practices, considering that observation time in the field is limited. Ideally, this will lead to a unified setup and nomenclature, facilitating better compatibility from data collected by different groups on ice sheets, shelves, and glaciers.