Near real time surface velocity measurements of North-East Greenland Ice Stream outlet glaciers from Sentinel-1A data

Compared to the western and southern parts of the Greenland ice sheet, where narrow tidewater and land terminating glaciers dominate, the north-eastern part is characterized by a major ice stream, the North-East Greenland Ice Stream (NEGIS), which drains about 8% of the ice sheet via three outlet glaciers. While the mass loss of the ice sheet was most prominent in the southern and western areas in the past decade, within the past few years also the north-eastern part showed changes. Therefore, a continuous monitoring of surface velocities of the large outlet glaciers Nioghalvfjerdsfjorden (79 NG) and Zachariae Isstrøm (ZIS) is intended. For this purpose we make use of Sentinel-1a data, aiming at near real time velocity measurements. Surface velocities are calculated for every 12-day and 24-day repeat pass by means of offset intensity tracking. Here we make use of Terrain Observation with Progressive Scans SAR (TOPSAR) Single Look Complex (SLC) data and precise orbit information. In order to achieve robust velocity fields and to close data gaps, offset tracking results are stacked on a monthly basis resulting in a continuous time series of velocity measurements since December 2014