Abstract
Abstract. Consistent and continuous data on glacier surface velocity are important inputs to time series analyses, numerical ice dynamic modeling and glacier mass flux computations. Since 2014, repeat-pass synthetic aperture radar (SAR) data have been acquired by the Sentinel-1 satellite constellation as part of the Copernicus program of the EU (European Union) and ESA (European Space Agency). It enables global, near-real-time-like and fully automatic processing of glacier surface velocity fields at up to 6 d temporal resolution, independent of weather conditions, season and daylight. We present a new global data set of glacier surface velocities that comprises continuously updated scene-pair velocity fields, as well as monthly and annually averaged velocity mosaics at 200 m spatial resolution. The velocity information is derived from archived and new Sentinel-1 SAR acquisitions by applying a well-established intensity offset tracking technique. The data set covers 12 major glacierized regions outside the polar ice sheets and is generated in an HPC (high-performance computing) environment at the University of Erlangen-Nuremberg. The velocity products are freely accessible via an interactive web portal that provides capabilities for download and simple online analyses: http://retreat.geographie.uni-erlangen.de (last access: 6 October 2021). In this paper, we give information on the data processing and how to access the data. For the example region of Svalbard, we demonstrate the potential of our products for velocity time series analyses at very high temporal resolution and assess the quality of our velocity products by comparing them to those generated from very high-resolution TerraSAR-X SAR and Landsat-8 optical (ITS_LIVE, GoLIVE) data. The subset of Sentinel-1 velocities for Svalbard analyzed in this paper is accessible via the GFZ Potsdam Data Services under the DOI https://doi.org/10.5880/fidgeo.2021.016 (Friedl et al., 2021). We find that Landsat-8 and Sentinel-1 annual velocity mosaics are in an overall good agreement, but speckle tracking on Sentinel-1 6 d repeat acquisitions derives more reliable velocity measurements over featureless and slow-moving areas than the optical data. Additionally, uncertainties of 12 d repeat Sentinel-1 mid-glacier scene-pair velocities have less than half (< 0.08 m d−1) of the uncertainties derived for 16 d repeat Landsat-8 data (0.17–0.18 m d−1).
Highlights
Glaciers are very sensitive indicators of global climate change (Bojinski et al, 2014) since recent atmospheric warming (Allen et al, 2018) has a direct or indirect influence on their mass balances (Zemp et al, 2019) and dynamics (Jiskoot, 2011)
We presented a new data set of scene-pair, as well as monthly and annually averaged, 200 m ice velocity grids
In contrast to existing data sets based on Landsat imagery, we are able to provide continuous glacier velocity time series all year round independent of weather conditions and sun illumination at very short sampling intervals of up to < 6 d in regions that are covered by multiple overlapping orbits with a 6 d repeat cycle
Summary
Glaciers are very sensitive indicators of global climate change (Bojinski et al, 2014) since recent atmospheric warming (Allen et al, 2018) has a direct or indirect influence on their mass balances (Zemp et al, 2019) and dynamics (Jiskoot, 2011). Global ice surface velocities are currently available from the ITS_LIVE (Gardner et al, 2018, 2019) and the GoLIVE (Scambos et al, 2016; Fahnestock et al, 2016) data sets, which both use optical Landsat data as input for the velocity calculations. We present a new near global data set of Sentinel-1 glacier velocities in 12 regions outside the polar ice sheets (Fig. 1) that comprises scene-pair velocity fields, as well as monthly and annual velocity mosaics derived from applying intensity offset tracking on both archived (since 2014) and the continuous stream of new acquisitions. On Svalbard, there are ice caps and ice fields with almost featureless surfaces, as well as surging glaciers that are prone to very rapid and strong accelerations
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