MEaSUREs Greenland Ice Sheet Velocity Map from InSAR Data


This data set, part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program, contains five seasonal ice-sheet-wide velocity maps for Greenland derived from Interferometric Synthetic Aperture Radar (InSAR) data. Velocity maps sourced from RADARSAT-1 data are available for the winters of 2000-2001, 2005-2006, 2006-2007, and 2007-2008. A velocity map constructed from the Advanced Land Observation Satellite (ALOS) and TerraSAR-X data is available for 2008-2009. For maps of glacier outlet areas, some of which demonstrated profound velocity changes during the observation period, see the related data set MEaSUREs Greenland Ice Velocity: Selected Glacier Site Velocity Maps from InSAR.

Note: Although these data sets have been screened for anomalously large errors, at this stage they are Version 1 products and some significant errors may persist (>20 m/yr). See the Error Estimates section of this documentation for details. In addition, these data are considered provisional pending a review by the MEaSUREs program. Once the data have been reviewed, this statement will be removed.

Citing These Data

Literature Citation

We kindly request that you acknowledge the use of this data set by referencing the following peer-reviewed publication.

Joughin, I., B. Smith, I. M. Howat, T. Scambos, and T. Moon. 2010. Greenland Flow Variability from Ice-Sheet-Wide Velocity Mapping. Journal of Glaciology, 56 (197), pp. 415-430, doi: 10.3189/002214310792447734.

Data Citation

As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Joughin, I., B. Smith, I. Howat, and T. Scambos. 2010. MEaSUREs Greenland Ice Velocity Map from InSAR Data. Boulder, Colorado, USA: NASA DAAC at the National Snow and Ice Data Center. doi:10.5067/MEASURES/CRYOSPHERE/nsidc-0478.001

Overview Table

Category Description
Data format GeoTIFF (.tif)
Spatial coverage and resolution Southernmost Latitude: 60° N
Northernmost Latitude: 83° N
Westernmost Longitude: 75° W
Easternmost Longitude: 14° W

500-meter gridding
Temporal coverage and resolution 2000 to 2001
2005 to 2006
2006 to 2007
2007 to 2008
2008 to 2009
File naming convention greenland_vel_mosaic500_2000_2001.tif
File size Data files are approximately 66 MB each.
Parameter(s) Ice velocity
Version V1.1. See the Version History section of this document for version information.
Procedures for obtaining data Data are available via FTP.

Table of Contents

  1. Contacts and Acknowledgments
  2. Detailed Data Description
  3. Data Access and Tools
  4. Data Acquisition and Processing
  5. References and Related Publications
  6. Document Information

1. Contacts and Acknowledgments


Dr. Ian Joughin
University of Washington
Applied Physics Laboratory
1013 NE 40th Street
Box 355640
Seattle, Washington 98105

Dr. Ben Smith
University of Washington
Polar Science Center Applied Physics Laboratory
University of Washington
Department of Earth and Space Sciences
Seattle, Washington 98195

Dr. Ian Howat
Ohio State University
Byrd Polar Research Center
Scott Hall Room 108
1090 Carmack Road
Columbus, Ohio 43210

Dr. Ted Scambos
University of Colorado
Cooperative Institute for Research in Environmental Science
National Snow and Ice Data Center
Boulder, Colorado 80309

Technical Contact

NSIDC User Services
National Snow and Ice Data Center
University of Colorado
Boulder, CO 80309-0449  USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services


These data were generated through a grant from the NASA MEaSUREs program.

2. Detailed Data Description


Data are available in GeoTIFF (.tif) format. For each mosaic, five GeoTIFF files are available: the velocity map, a component velocity map in the x-direction (vx), a component velocity map in the y-direction (vy), error estimates in the x-direction (ex), and error estimates in the y-direction (ey).

File and Directory Structure

Data are available on the FTP site in the directory.

File Naming Convention

The file naming convention used for this data set is:



Table 3. File Naming Convention
Variable Description
greenland_vel_mosaic500_ Greenland 500 m velocity mosaic
yyyy_yyyy Winter season
vx OR vy velocity x-direction, velocity y-direction
ex OR ey error x-direction, error y-direction
.tif GeoTIFF-formatted file

File Size

Each data file is approximately 66 MB. The entire data volume (25 files) is 1.64 GB.

Spatial Coverage

This data set covers the entire expanse of Greenland.

Southernmost Latitude: 60° N
Northernmost Latitude: 83° N
Westernmost Longitude: 75° W
Easternmost Longitude: 14° W

Spatial Resolution

500 m


Data are provided in polar stereographic coordinates with a standard latitude of 70° N and rotation angle of -45° (sometimes specified as a longitude of 45° E). With this convention, the x-axis extends south from the North Pole along the 45° E meridian.

Temporal Coverage

The data set currently provides velocity mosaics for the winters of 2000 – 2001; 2005 – 2006; 2006 – 2007; 2007 – 2008; and 2008 – 2009.

Parameter or Variable

Velocities are reported in meters per yer. The vx and vy files contain component velocities in the x and y directions defined by the polar stereographic grid. These velocities are true values and not subject to the distance distortions present in a polar stereographic grid. Small holes have been filled via interpolation in some areas. Interpolated values are identifiable as locations that have velocity data but no error estimates. Radar-derived velocities are determined using a combination of conventional InSAR and speckle tracking techniques (Joughin, et. al., 2002).

Error estimates are provided for all non-interpolated, radar-derived velocity vectors in separate GeoTIFF files appended with _ex.tif and _ey.tif. These estimates include the statistical uncertainty associated with the phase and speckle tracking error. Formal errors agree reasonably well with errors determined by comparison with GPS data (Joughin, et al, 2002). The values, however, underestimate true uncertainty in several ways (see Error Sources for more details) and as such should be used more as an indication of relative quality rather than absolute error.

Error Sources

These data sets have been screened for anomalously large errors, but at this stage they are version 1 products and some significant errors may persist (>20 m/yr). In particular, a bad InSAR baseline fit may bias the ice velocities over wide regions (for example across single or multiple adjacent swaths) by tens of meters per year. Once the first round of processing is complete, the investigators will perform an inter-annual comparison to help screen out or correct problem (for example outlier) tracks. Users who find such anomalies should report them to NSIDC and the PI at, to facillitate their removal in the next round of processing.

In addition to errors, please note that velocities in the interior (roughly >100 km from the coast) are determined using baseline fits to a common set of ground control points (balance and GPS velocities at elevations >2000 m), under the assumption that slow-moving ice far from the coast is changing only slowly (Joughin et al, 2010). While less than ideal, this assumption produces far smaller errors than using no control. Caution should be taken when interpreting any apparent changes in ice flow speed in areas >100 km from the coast. In coastal regions, the velocities are referenced to rock and more accurately represent ice velocity and its temporal evolution. Users should be aware the potential for anomalously large errors exists. If in doubt, please contact NSIDC and the PI at for verification.

Swath data are broken into overlapping sections during processing and estimates may be double averaged in regions of overlap, causing errors to be underestimated by 1/sqrt(2) in these regions. Error estimates are derived from local statistics, so errors may be overstated near shear margins and other areas with strong velocity gradients. Errors associated with the baseline solutions are not included in the error estimates. These are generally small (<5 m/yr) but can be larger in interior areas away control points derived from rock on the coast or balance velocities near the divides. The error estimates also do not account for ionospheric streak errors, which tend to be the worst in northwest Greenland near the magnetic north pole. These errors range from severe (>10 m/yr) in the 2000-2001mosaic (near the solar maximum) to almost negligible in the years after 2005. Absolute errors in the DEM used for processing introduce only small errors, but slope errors in the DEM can produce errors of up to about three percent of the observed speed. The formal errors plus three percent are a good rule of thumb to use except in cases where streaks suggest substantially larger errors.

See Joughin, et al, 2002 for more detail on errors and how they are computed.

3. Data Access and Tools

Data Access

Data are available via FTP.


Total volume of the data set is approximately 500 MB.

Software and Tools

GeoTIFF files can be viewed with a variety of Geographical Information System (GIS) software packages including Blue Marble Geographics Global Mapper and Esri ArcGIS.

Related Data Collections

4. Data Acquisition and Processing

Theory of Measurements

The velocity maps in this data set were created using SAR data from the RADARSAT satellite. The methods included a combination of speckle tracking and conventional interferometry. Annual velocity maps were produced by mosaicking multiple strips of InSAR-derived data. The individual mosaic images were selected to satisfy two criteria: first, the images came from the same time of year, and second, the images for each individual year were collected in as short a period of time as possible. For more detail, please see Joughin, et. al,. 2002.

Sensor or Instrument Description

2000 to 2001 Mosaic

In late 2000 and early 2001, during the RADARSAT-1 Modified Antarctic Mapping Mission, the Canadian Space Agency (CSA) acquired nearly complete coverage of Greenland with multiple passes suitable for InSAR (September 3 to January 24). All of the available data for Greenland were used to produce the 2000 to 2001 mosaic. In cases where the data quality was too poor, some products were discarded. All source data were obtained from the Alaska Satellite Facility (ASF).

2005 to 2006 Mosaic

In 2005 and 2006, RADARSAT-1 imaged most of Greenland four consecutive times, producing three InSAR pairs. All of the data were processed. Poor coherence passes were screened out, and the remaining data were used to assemble the mosaic.

2006 to 2007 Mosaic

The 2006/2007 mosaic was produced with RADARSAT-1 fine beam data collected from 18 December 2006 and 15 April 2007. Fine beam data are intended for applications which require the best spatial resolution available from RADARSAT. The azimuth resolution is 8.4m, with range resolution 9.1m to 7.8m; the incidence angle range is 37 to 47 degrees.

2007 to 2008 Mosaic

The 2007/2008 mosaic was produced with RADARSAT-1 fine beam data, in the same manner as the 2006/2007 mosaic.

2008 to 2009 Mosaic

The 2008/2009 mosaic was produced with ALOS and TerraSAR-X data.

Derivation Techniques and Algorithms

Annual mosaics were created using data collected over an approximately 96-day period during the winter. Areas with no data correspond to either regions where no data were acquired or where the interferometric correlation was insufficient to produce an estimate, most often in areas with high snow accumulation. Regions with data represent the average of between one and three estimates (larger numbers may occur in regions of swath overlap, especially at higher latitudes).

The data are posted on a 0.5-kilometer grid, but the true resolution varies between 0.5 and 1 km. Many small glaciers are resolved outside the main ice sheet, but it is important to remember that for narrow (<1km) glaciers, the velocity represents an average of both moving ice and stationary rock, so while the glacier may be visible in the map, its speed is likely underestimated. Also on some of the smaller glaciers, interpolation produces artifacts where the interpolated value is derived from nearby rock, causing apparent stationary regions in the middle of otherwise active flow. The data have been screened to remove most of these, but please proceed with caution.

Version History

Version 1.1 was released August, 2015. Refer to Table 4 for this data set's version history:

Table 4. Version History
Version Description
V1.1 Binary data file format discontinued. Data available in GeoTIFF only (August, 2015).
V1 Initial version (September, 2010)


5. References and Related Publications

Joughin, I. 1995. Estimation of Ice-Sheet Topography and Motion Using Interferometric Synthetic Aperture Radar. (PhD Dissertation, University of Washington).

Joughin, I. 2002. Ice-Sheet Velocity Mapping: A Combined Interferometric and Speckle-Tracking Approach. Annals of Glaciology 34: 195-201. doi:10.3189/172756402781817978.

Joughin, I., S. Tulaczyk, R. Bindschadler, and S. F. Price. 2002. Changes in West Antarctic Ice Stream Velocities: Observation and Analysis. Journal of Geophyscial Research-Solid Earth, 107(B11), 2289. doi:10.1029/2001JB001029.

Joughin, I., W. Abdalati and M. Fahnestock. 2004. Large Fluctuations in Speed on Greenland's Jakobshavn Isbrae Glacier. Nature, 432(7017): 608-610. doi:10.1038/nature03130.

Moon, T. and I. Joughin 2008. Retreat and Advance of Greenland Tidewater Glaciers from 1992 to 2007. Journal of Geophysical Research Earth Surface, 113: F02022, doi:10.1029/2007JF000927.

Rignot, E. and P. Kanagaratnam. 2006. Changes in the Velocity Structure of the Greenland Ice Sheet. Science, 311(5763): 986-990. doi:10.1126/science.1121381.

Joughin, I., B. Smith, I. M. Howat, T. Scambos, and T. Moon. 2010. Greenland Flow Variability from Ice-Sheet-Wide Velocity Mapping. Journal of Glaciology, 56 (197), pp. 415-430, doi:10.3189/002214310792447734.

The following related documents are available

Table 5. Related Documents
Document Description URL
Alaska Satellite Facility ASF Web site
MEaSUREs Data Web site NSIDC data Web site
NASA MEaSUREs Web site NASA Measures Projects Web site

6. Document Information


The following acronyms are used in this document.

Table 6. Acronyms and Abbreviations
Acronym Description
FTP File Transfer Protocol
GeoTIFF Geospatial Tagged Image File Format
InSAR Interferometric Synthetic Aperture Radar
MEaSUREs Making Earth System Data Records for Use in Research Environments
ALOS Advanced Land Observation Satellite
NSIDC National Snow and Ice Data Center
URL Uniform Resource Locator

Document Creation Date

September, 2010

Document Revision Date

August, 2015

Document URL