New Insights into Structures Within the Ross Ice Shelf from ROSETTA-Ice Radar Surveys

Abstract:

Ice penetrating radar is one of the most efficient tools for visualizing ice sheets and ice shelves. Radar echograms are an effective resource to analyze ice dynamics and stability. From 2015 to 2017, the ROSETTA-Ice Project surveyed the Ross Ice Shelf using two radar systems onboard the IcePod, a multi-sensor aerogeophysical platform. The survey grid consisted of East-West lateral lines spaced ~10 kilometers apart, and North-South tie lines spaced 55km apart. The deployed radar were designed as high resolution short range and long range tandem units. When flying at an elevation of ~750 meters: the Shallow Ice Radar (SIR) has a maximum imaging depth of ~415 meters below the ice surface; and the Deep ICE (DICE) radar has a maximum imaging depth of ~3,000 meters. With about 55,000 kilometers of survey line data collected, the ROSETTA-Ice radar dataset is enormous and gives an unprecedented view inside the Ross Ice Shelf system.

The visualized echograms offer a unique view of the structure of the interior of the Ross Ice Shelf. For example, within the SIR echograms: thin layering of local meteoric ice (LMI) is clearest in areas with stagnant ice, like Minna Bluff; as well as, a series of bright, distinctly shaped packets of continental meteoric ice (CMI) appear throughout the interior of the ice shelf and follow glacier streamlines. The survey coverage allows features to be identified and traced throughout the shelf, from grounding zone to calving front. Surface features of shear margins, crevasses, and rifts have been mapped from extensive satellite imagery of the ice surface and are here correlated with features from the base and the interior of the ice shelf.

Horizons were picked within echograms by loading individual radar frames of ~5 minute flight duration, which is efficient, but loses spatial context. Generating full-line, georeferenced images provides context for interpretation because it enables the survey lines to be viewed simultaneously. Full-line images have been inserted into Microsoft’s Augmented Reality (AR) headset and a desktop-enabled proprietary 3-Dimensional imaging software, putting the echograms in further geospatial context. We use these techniques to present a virtual tour of the Ross Ice Shelf and provide a framework for observation-driven enquiries into ice shelf processes.