Measuring Ice Sheet Surface Elevation Change in the Greenland Ice Sheet Ablation Zone From Repeat Terrestrial LIDAR Surveys

Direct measurements of Greenland Ice Sheet surface ablation are important for calibrating and validating surface mass balance models as well as airborne and spaceborne data products. Most measurements of ice surface ablation rely on rates of surface lowering measured at a few sparse locations using bamboo stakes or non-contact sonic sensors. However, these point-based surface ablation rates may not be representative across broader spatial scales because they fail to account for variable topography, solar geometry, and surface albedo. To understand spatially-variable ablation rates, we used a Riegl VZ-400 terrestrial LIDAR scanner (TLS) to monitor sub-daily ablation rates at three 100m plots in the ablation zone of the Greenland Ice Sheet for a week in July 2016. The first plot includes a supraglacial meltwater channel, a melt pond and the contributing channel bank which is temporarily inundated each day due to diurnal variations in meltwater production. The second plot covers a relatively flat ice surface that is free of noteworthy meltwater channels or ponds but contains distributed cryoconite holes and distributed surface impurities that locally influence albedo. The third plot covers a vertically incised canyon that channels a supraglacial meltwater and receives highly variable solar radiation due to local topography and solar geometry. The three plots span a range of topographic, geometric and albedo variations found across the Greenland Ice Sheet ablation zone . We conclude that this novel application of TLS technology provides spatially accurate, representative measurements of surface ablation across larger areas with less interpolation and less time spent on collection and analysis when compared to traditional manual point-based methods alone. Eventually, this technology may allow automated surveying of ice surface ablation year-round.