Day 4

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Paper title Can ice velocity changes be detected in interior Greenland? - an assessment of ice velocities derived from satellite data by GPS in the Northeast Greenland Ice Stream (NEGIS)
  1. Christine S Hvidberg University of Copenhagen Speaker
  2. Aslak Grinsted UnivCopenhagen
  3. Nicholas M Rathmann UnivCopenhagen
  4. Dorthe Dahl-Jensen UnivCopenhagen
  5. Shfaqat Abbas Khan
  6. Anders Kusk DTU Space - Technical University of Denmark
  7. Jonas Kvist Andersen DTU Space - Technical University of Denmark
  8. Niklas Neckel Alfred Wegner Institute Helmholtz Centre for Polar and Marine Science
  9. Anne M. Solgaard GEUS
  10. Nanna B Karlsson Geological Survey of Denmark and Greenland (GEUS)
  11. Helle A Kjær UnivCopenhagen
  12. Paul Vallelonga UnivCopenhagen
Form of presentation Poster
  • A9. Polar Science and Cryosphere
    • A9.04 Mass Balance of the Cryosphere
Abstract text The Northeast Greenland Ice Stream (NEGIS) extends around 600 km upstream from the coast to its onset near the ice divide in interior Greenland. Several maps of surface velocity and topography in the interior Greenland exist, but the accuracy is not well constrained by in situ observations limiting detailed studies of flow structures and shear margins near the onset of NEGIS. Here we present an assessment of a list of satellite-based surface velocity products by GPS in an area located approximately 150 km from the ice divide near the East Greenland Ice-core Project (EastGRIP) deep drilling site (75°38’ N, 35°60’ W). For the evaluation of the satellite-based ice velocity products, we use data from a GPS mapping of surface velocity over the years 2015-2019. The GPS network consists of 63 poles and covers an area of 35 km along NEGIS and 40 km across NEGIS, including both shear margins. The GPS observations show that the ice flows with a uniform surface speed of approximately 55 m a-1 within a >10 km wide central flow band which is clearly marked from the slow moving ice outside NEGIS by 10-20 m deep shear margins. The GPS derived velocities cover a range of velocities between 6 m a-1 and 55 m a-1, with strain rates in the order of 10-3 a-1 in the shear margins. We compare the GPS results to the Arctic Digital Elevation Model (ArcticDEM) and a list of 165 published and experimental remote sensing velocity products from the NASA MEaSUREs program, the ESA Climate Change Initiative, the PROMICE project and three experimental products based on data from the ESA Sentinel-1, the DLR TerraSAR-X, and USGS Landsat satellites. For each velocity product, we determine the bias and precision of the velocity compared to the GPS observations, as well as the smoothing of the velocity products needed to obtain optimal precision. The best products have a bias and a precision of ~0.5 m a-1. We combine the GPS results with satellite-based products and show that ice velocity changes in the interior of NEGIS are generally below the accuracy of the satellite products. However, it is possible to detect changes in large-scale patterns of ice velocity in interior northeastern Greenland using satellite based data that are smoothed spatially and using very long observational periods of decades, suggesting dynamical changes in the upstream legs of the NEGIS outlets. This underlines the need for long satellite based data products to monitor the interior part of the ice sheet and its response to climate change.