Improving Radiometric Resolution for High Fidelity Measurements of Subglacial Conditions

Abstract:

Radar sounding is an influential remote sensing technique used frequently to study and characterize ice sheet subsurface conditions. Radar echoes reflected from the bed directly measure ice sheet basal conditions, including hydrology, roughness, and thermal state, as well as englacial effects such as ice column density and temperature. However, these signatures produce non-unique responses in the radar echo, making direct interpretation of glaciological conditions extremely challenging. Current approaches to facilitate interpretation require analysis of relative spatial patterns and/or significant assumptions on the ice sheet basal conditions. None of the existing approaches are able to definitively resolve individual effects within a radar echo, and in particular none are able to separate basal roughness from basal material signatures.

To overcome this challenge, we have developed a multi-frequency radar sounding approach that uses the frequency-dependent basal roughness signature to remove roughness effects and isolate the basal material signature within a bed echo. This approach enables high fidelity interpretation of basal reflectivity and thus, basal thermal state, material, and potentially saturation/porosity. To produce high confidence interpretations, we require a radar sounder with high radiometric resolution and frequencies spanning several orders of magnitude. Here we investigate the impacts of multi-looking, signal-to-noise ratio (SNR) and coherent processing on radiometric resolution in a multi-frequency system. We also discuss the effect of different basal roughness regimes on radar system and experimental designs focused on increasing radiometric resolution.