Post-Processing Synchronized Bistatic Radar for Long Offset Glacier Sounding
Nicole Bienert, Dustin M. Schroeder, Sean T. Peters, Emma MacKie, Eliza Dawson, Matthew R. Siegfried, Rohan Sanda, Poul Christoffersen
Abstract
Radar tomography of glaciers promises to improve imaging and estimates of subsurface ice-sheet structures and properties, including temperature distributions, basal materials, ice fabric, and englacial water content. However, bistatic radar data with long (i.e., larger than the ice thickness) walk-away surveys are required to constrain high-fidelity tomographic inversions. These long-offset data have proven difficult to collect due to the hardware complexity of existing synchronization techniques. Therefore, we remove the hardware complexity required for real-time synchronization by synchronizing in postprocessing. Our technique transforms an Autonomous phase-sensitive Radio Echo Sounder (ApRES) system and a software-defined radio receiver into a coherent bistatic radar capable of recovering basal echoes at long offsets. We validated our system at Whillans Ice Stream, West Antarctica, with a walk-away survey up to 1300 m (797 m thick) and at Store Glacier, Greenland, up to 1450 m (1028 m thick). At both field sites, we measured the basal echo at angles beyond the point of total internal reflection (TIR), whose previous literature had set as a hard physical limit. We support our experimental results with high-frequency structure simulation, which shows that ground-based radar systems capture evanescent waves and are not hindered by TIR. Our analysis and experiments demonstrate a system capable of executing wide-angle bistatic radar surveys for improved geometric and radiometric resolution of inversions for englacial and subglacial properties.