TESTING THE POTENTIAL FOR REPEAT STRUCTURE-FROM-MOTION PHOTOGRAMMETRIC SURVEYS TO DETERMINE MASS BALANCE AND MELTWATER DISCHARGE, EASTON GLACIER, MT. BAKER, WA

Traditional methods of measuring glacier mass balance (MB) are labor-intensive and rely on broad extrapolation of sparse ablation stake data to assess mass change across the glacier. In this study, we test the ability of repeat high-resolution Structure-from-Motion (SfM) surveys of a glacier to mimic (or improve on) a traditional field-based MB study. For the test, we established a traditional MB survey by installing five ablation stakes at regular intervals along a transect up the Easton Glacier, Mount Baker, WA. We revisited the stakes 3-5 times throughout the late spring and summer to record snow and ice melt (and any accumulation) between subsequent field visits; net accumulation, ablation, and MB are calculated by extrapolating the stake measurements across altitudinal swaths centered on each stake. To assess meltwater discharge below the Easton Glacier, we installed level-logger stream gauges in two outlet creeks below the terminus to record a continuous time series of stream stage. We established rating curves at each site with in-stream discharge measurements over the summer. For the SfM comparison survey, we will combine high-resolution imagery from unmanned aerial vehicles (UAV) with Digital Globe satellite stereo imagery (e.g. Shean et al., 2016) to create digital elevation models (DEMs) to approximate maximum accumulation (May 2018) and maximum ablation (September 2018) for the glacier. By differencing the DEMs, we produce distributed MB estimates for the entire glacier. The traditional MB survey records high ablation rates related to an unusually warm, dry summer. Rates of melt increase substantially between July and September, as ice was exposed at the lower two stakes. Despite 542.6 cm of snow melt at Stake 3 through the ablation season, ice was not exposed. At the meeting, we will present results of an on-going comprehensive analyses of the distributed glacier MB, and its comparison to the SfM survey data.