Polarimetric multi-offset radio-echo sounding with a radio frequency-over-fiber ApRES system

Abstract Polarimetric multi-offset radio-echo sounding offers improved constraints on englacial thermal conditions, basal properties and ice crystal orientation compared to standard monostatic observations. Nevertheless, such surveys are uncommon in glaciology and are typically limited in offset due to cable losses. In the 2023–24 austral summer, we deployed two radar systems on Eastwind Glacier and the McMurdo Ice Shelf in Antarctica, collecting five polarimetric common-midpoint (CMP) surveys. Using an Autonomous phase-sensitive Radio-Echo Sounder (ApRES), modified with off-the-shelf radio frequency-over-fiber (RFoF) hardware and a low-loss fiber optic link, we detect bed reflections at offsets up to the equivalent of four ice thicknesses, well beyond the theoretical point of total internal reflection. A second, cable-less system built around a software-defined radio (SDR) was deployed simultaneously as an unsynchronized receiver recording the same ApRES transmitter. These co-located datasets demonstrate the potential for cabled radar systems with integrated RFoF technology for extending maximum offsets by overcoming attenuation losses inherent to coaxial cables. Furthermore, we perform polarimetric amplitude-vs-offset analysis to probe glacier dielectric structure. Finally, we present data from deployment of the fiber optic system on Thwaites Glacier, where we detect bed reflections at an offset of 4 km, demonstrating operation on thick ice (~2.2 km).