We derive surface ice velocity using data from 16 satellite sensors deployed by 6 different space agencies. The list of sensors and the year that they were used are listed in the following (Table S1). The SAR data are processed from raw to single look complex using the GAMMA processor (www.gamma-rs.ch). All measurements rely on consecutive images where the ice displacement is estimated from tracking or interferometry (Joughin et al. 1998, Michel and Rignot 1999, Mouginot et al. 2012). Surface ice motion is detected using a speckle tracking algorithm for SAR instruments and feature tracking for Landsat. The cross-correlation program for both SAR and optical images is ampcor from the JPL/Caltech repeat orbit interferometry package (ROI_PAC). We assembled a composite ice velocity mosaic at 150 m posting using our entire speed database as described in Mouginot et al. 2017 (Fig. 1A). The ice velocity maps are also mosaicked in annual maps at 150 m posting, covering July, 1st to June, 30th of the following year, i.e. centered on January, 1st (12) because a majority of historic data were acquired in winter season, hence spanning two calendar years.

We use Landsat-1&2/MSS images between 1972 and 1976 and combine image pairs up to 1 year apart to measure the displacement of surface features between images as described in Dehecq et al., 2015 or Mouginot et al. 2017. We use the 1978 2-m orthorectified aerial images to correct the geolocation of Landsat-1 and -2 images (Korsgaard et al., 2016). Between 1984 and 1991, we processed Landsat-4&5/TM image pairs acquired up to 1-year apart. Only few Landsat-4 and -5 images (~3%) needed geocoding refinement using the same 1978 reference as used previously. Between 1991 and 1998, we process radar images from the European ERS-1/2, with a repeat cycle varying from 3 to 36 days depending on the mission phase. Between 1999 and 2013, we use Landsat-7, ASTER, RADARSAT-1/2, ALOS/PALSAR, ENVISAT/ASAR to determine surface velocity (Joughin et al., 2010; Howat, I. 2017; Rignot & Mouginot, 2012). After 2013, we use Landsat-8, Sentinel-1a/b and RADARSAT-2 (Mouginot et al., 2017). All synthetic aperture radar (SAR) datasets are processed assuming surface parallel flow using the digital elevation model (DEM) from the Greenland Mapping Project (GIMP; Howat et al., 2014) and calibrated as described in Mouginot et al., 2012, 2017.

Data were provided by the European Space Agency (ESA) the EU Copernicus program (through ESA), the Canadian Space Agency (CSA), the Japan Aerospace Exploration Agency (JAXA), the Agenzia Spaziale Italiana (ASI), the Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) and the National Aeronautics and Space Administration (NASA). SAR data acquisition were coordinated by the Polar Space Task Group (PSTG).

References:

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Howat, I (2017). MEaSUREs Greenland Ice Velocity: Selected Glacier Site Velocity Maps from Optical Images, Version 2. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center.

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