Investigating Ice Surface Elevations Derived from Laser and Radar-sounding Measurements Over Devon Ice Cap, Canadian Arctic

Knowledge of accurate ice surface elevations is important to many glaciological applications on Earths' glaciers and ice sheets. Changes in ice surface elevation are widely used to estimate glacier mass balance, whereas accurate surface elevations are crucial when deriving subglacial water flow paths. Spatially extensive ice surface elevations are commonly derived via satellite measurements or from airborne surveys via laser altimetry or radar-sounding measurements. However, these techniques are sensitive to different penetration depths of the returned signal in snow/firn/ice, resulting in derived surface elevation offsets when measured from different instruments.

Over Devon Ice Cap (DIC), Canadian Arctic, we observe an offset between laser and radar derived ice surface elevations, with the radar derived surface elevation being up to ~20 meters below the laser measurements in certain areas. Here, we investigate the sensitivity of this offset to the near-surface firn structure. To identify possible causes for this offset, we compare the spatial pattern of the observed surface elevation offset to the near-surface firn structure, which has been well characterized from ground-based observations (using firn cores and radar-sounding) and applications of the Radar Statistical Reconnaissance method to airborne radar-sounding measurements. DIC consists of heterogeneous near-surface firn that contains massive ice layers from percolated, refrozen surface meltwater within specific elevation ranges. Preliminary results suggest that the most significant elevation offset between the laser and radar measurements coincides with a region in which firn consists of complex ice layers. This suggests a connection between the elevation offset and the presence of ice layers in the near-surface firn. Results from this study can improve our understanding of near-surface effects on the radar-sounding surface returns, and thus assess uncertainties in their derived surface elevations. This is particularly important in areas where no laser altimetry measurements exist (e.g. Europa Clipper mission or cloud cover). In addition, results from this study could help the characterization of the near-surface firn structure on other glaciers and ice sheets via a comparison between laser and radar-derived surface elevations.