DOI: 10.7280/d1mm37
title: Annual Ice Velocity of the Greenland Ice Sheet (1972-1990)

description: 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 years 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) and the U.S. Geological Survey (USGS). SAR data
 acquisition were coordinated by the Polar Space Task Group (PSTG).
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