Investigating the radar response of englacial debris entrained basal ice units in East Antarctica using electromagnetic forward modelling

Radio-echo sounding reveals patches of high backscatter in basal ice units, which represent distinct englacial features in the bottom parts of glaciers and ice sheets. Their material composition and physical properties are largely unknown due to their direct inaccessibility but could provide significant information on the physical state as well as on present and past processes at the ice-sheet base. Here, we investigate the material properties of basal ice units by comparing measured airborne radar data with synthetic radar responses generated using electromagnetic forward modelling. The observations were acquired at the onset of the Jutulstraumen Ice Stream in western Dronning Maud Land (East Antarctica) and show strong continuous near-basal reflections of up to 200m thickness in the normally echo-free zone. Based on our modelling, we suggest that these high-backscatter units are most likely composed of point reflectors with low-dielectric properties, suggesting thick packages of englacial entrained debris. We further investigate the effects of entrained particle size, and concentration in combination with different dielectric properties, which provide useful information to constrain the material composition of radar-detected units of high backscatter. The capability and application of radar wave modelling in complex englacial environments is therefore a valuable tool to further constrain the composition of basal ice and the physical conditions at the ice base.