DOI: 10.7280/d10d4z
title: Phase-Based Antarctica Ice Velocity Map

description: Complete map of ice motion in Antarctica combining phase data in the
 interior and speckle tracking in the fast-moving sectors. We present a new
 map of Antarctic ice velocity that is ten times more precise than prior
 maps and reveals ice motion at a high precision over 80% of the continent
 versus 20% in the past. The ice motion vector map provides novel
 constrains on interior ice motion and its connection with the glaciers and
 ice stream that control the stability and mass balance of the Antarctic
 Ice Sheet.
description: This mosaic is
 a merge between phase-derived velocity and the earlier mosaic of ice
 velocity derived from speckle and feature tracking (Mouginot et al.,
 2017). Where available, the phase data takes priority. At the transition
 boundary, we apply a feathering technique to minimize the discontinuity in
 velocity and in spatial derivative in both horizontal directions, but
 preserving the phase data. For the phase, we rely on
 the entire SAR archive since 1992 with six sensors from multiple space
 agencies. The data are the Canadian Space Agency (CSA) with RADARSAT-1 and
 RADARSAT-2, the European Space Agency (ESA) with the Earth Remote Sensing
 Satellites 1-2 (ERS-1/2) and the Envisat ASAR; the Japan Aerospace
 Exploration Agency (JAXA) with ALOS PALSAR-1 and a few scenes from ALOS2
 PALSAR. We do not include data from the European Copernicus Sentinel-1a/b
 SARs because the TopSAR acquisition mode of the Sentinel-1a/b data
 produces residual phase jumps at burst boundaries that make it impractical
 for precision phase-mapping, even with data stacking and additional
 corrections (Scheuchl et al., 2016). Each sensor has its own advantage and
 inconvenience: Envisat ASAR and RADARSAT-2 are the only sensors providing
 descending passes over East Antarctica. ALOS PALSAR-1 provides ascending
 passes with a high temporal coherence along the periphery. RADARSAT-2
 provides the most complete dataset with coverage of the southernmost
 regions including ascending and descending passes in left looking mode and
 right looking coverage with ascending and descending passes similar to
 Envisat ASAR. ERS-1/2 provides high coherence images (1-day repeat) over
 rapidly changing sectors of West Antarctica. Phase-derived velocity are
 mostly for years between 2007 and 2018 while regions covered by speckle-
 tracking-derived velocity (along the coasts) are mostly representative of
 years 2013-2017. SAR and interferogram processing, unwrapping and
 geocoding were done using GAMMA remote sensing
 processor.
description: The data are formatted in Network Common Data Form, Version 4
 (NetCDF-4) (.nc) following version 1.6 of the Climate and Forecast (CF)
 metadata conventions. For more information about working with NetCDF
 formatted data, visit the UCAR Unidata Network
 Common Data Form Web site. This data set
 includes one file named <code>v_mix.v21May2019.nc</code> (450
 m grid spacing)<code>.</code>
 Spatial Coverage: The data
 set spans the continent of Antarctica. Southernmost
 Latitude: 90° S <br> Northernmost Latitude: 60° S <br>
 Westernmost Longitude: 180° W <br> Easternmost Longitude: 180°
 E Polar stereographic with true scale at 71° S. Refer
 to Polar
 Stereographic Projection and Grid page for more information and
 polar stereographic grid definitions. This data set
 provides a comprehensive ice velocity map of the Antarctic Ice Sheet
 posted at 450 m grid spacing. The velocity components for the x and y
 direction, as defined by the polar stereographic grid, are stored in the
 NetCDF variables
 named <code>VX</code> and <code>VY</code> and are
 recorded in m/yr. Error estimates for the velocity components are provided
 as
 variables <code>ERRX</code> and <code>ERRY</code>;
 however, these values should be used more as an indication of relative
 quality rather than absolute error. The data also include the standard
 deviations for the velocity estimates
 (<code>STDX,STDY</code>), as well as a count of scenes
 (<code>CNT</code>) used to estimate the values for each pixel.
 Finally, the data include the source for the velocity estimates
 (<code>SOURCE) </code>from tracking-based techniques
 (=1), phase-based techniques (=2), or interpolation between tracking- and
 phase-based techniques (=3). Data
 sources: 
 <strong>Platform/Sensor</strong>
 <strong>Space Agency</strong> 
 <strong>ERS-1 &
 2/SAR</strong> European Space Agency
 (ESA) 
 <strong>RADARSAT-1/SAR</strong>
 Canadian Space Agency (CSA) 
 <strong>ENVISAT/ASAR</strong>
 ESA 
 <strong>RADARSAT-2/SAR</strong>
 CSA 
 <strong>ALOS/PALSAR</strong>
 Japan Aerospace Exploration Agency (JAXA) 
 <strong>Sentinel-1a &
 b</strong> ESA 
 <strong>Landsat-8/OLI</strong>
 USGS/NASA 
 <strong>TanDEM-X/TerraSAR-X/SAR</strong>
 German Space Agency (DLR) 
 <strong>ALOS2/PALSAR2</strong>
 Japan Aerospace Exploration Agency (JAXA) 
  
 References and Related Publications:
 Michel, R., and E. Rignot. 1999. Flow of Glacier Moreno,
 Argentina, from Repeat-Pass Shuttle Imaging Radar Images: Comparison of
 the Phase Correlation Method with Radar Interferometry. <em>Journal
 of Glaciology</em> 45(149): 93-100. Mouginot, J.,
 et al. 2017. Comprehensive Annual Ice Sheet Velocity Mapping Using
 Landsat-8, Sentinel-1, and RADARSAT-2 Data. <em>Remote
 Sensing</em> 9(4): Art. #364. doi: 10.3390/rs9040364. Mouginot, J., E. Rignot, and B. Scheuchl. 2015. Sustained increase in ice discharge from the Amundsen Sea Embayment, West Antarctica, from 1973 to 2013. <em>Geophysical Research Letters</em> 41: 1576–1584. doi: 10.1002/2013GL059069. Mouginot, J., B. Scheuchl, and E. Rignot. 2012. Mapping of Ice Motion in Antarctica Using Synthetic-Aperture Radar Data. <em>Remote Sensing</em> 4(9): 2753-2767. doi: 10.3390/rs4092753. Rignot, E., J. Mouginot, and B. Scheuchl. 2011. Ice Flow of the Antarctic Ice Sheet. <em>Science</em> 333(6048): 1427-1430. doi: 10.1126/science.1208336. Rignot, E., J. Mouginot, and B. Scheuchl. 2011. Antarctic grounding line mapping from differential satellite radar interferometry. <em>Geophysical Research Lett</em>ers 38(10): Art. #L10504. doi: 10.1029/2011GL047109. Scheuchl, B., J. Mouginot, and E. Rignot. 2012. Ice velocity changes in the Ross and Ronne sectors observed using satellite radar data from 1997 and 2009. <em>The Cryosphere</em> 6: 1019-1030. doi: 10.5194/tc-6-1019-2012.