Repeat UAV photogrammetry to assess calving front dynamics at a large outlet glacier draining the Greenland Ice Sheet

To quantify the ice-ocean processes which drive dynamic and geometric change at calving outlet glaciers, detailed measurements beyond the capability of present satellites are required. This study presents the application of a cost-effective (< USD 2000), unmanned aerial vehicle (UAV) to investigate frontal dynamics at a major outlet draining the western sector of the Greenland Ice Sheet. The UAV was flown over Store Glacier on three sorties during summer 2013 and acquired over 2000 overlapping, geo-tagged images of the calving front at ∼40 cm resolution. Stereo-photogrammetry applied to these images enabled the extraction of high-resolution digital elevation models with an accuracy of ±1.9 m which we used to quantify glaciological processes from early July to August 2013. The central zone of the calving front advanced by ~500 m whilst the lateral margins remained stable. In addition, the ice surface thinned by 3.5 m m−1during the melt-season in association with dynamic thinning. Ice flux through the calving front is calculated at 2.96 × 107 m3 d−1, equivalent to 11 Gt a−1, which is comparable to flux-gate estimates of Store Glacier's annual discharge. Water-filled crevasses were observed throughout the observation period, but covered a limited area (1200 to 12 000 m2 of the ∼5 × 106 m2 surveyed area) and did not appear to exert any significant control over calving. We conclude that the use of repeat UAV surveys coupled with the processing techniques outlined in this paper have a number of important potential applications to tidewater outlet glaciers.