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Data Set ID:
NSIDC-0484

MEaSUREs InSAR-Based Antarctica Ice Velocity Map, Version 1

This data set (NSIDC-0484), part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) Program, provides the first comprehensive, high-resolution, digital mosaics of ice motion in Antarctica assembled from multiple satellite interferometric synthetic-aperture radar systems. The majority of the data were acquired during the International Polar Year 2007 to 2009. Additional data were utilized as needed to maximize coverage. Mosaics are available at 450 m and 900 m spacings.

Note: These data are considered provisional pending a review by the MEaSUREs program. Once the data have been reviewed, this statement will be removed from this documentation.

Geographic Coverage

Parameter(s):
  • Snow/Ice > Ice Velocity
Spatial Coverage:
  • N: -60, S: -90, E: 180, W: -180

Spatial Resolution:
  • 900 m x 900 m
  • 450 m x 450 m
Temporal Coverage:
  • 1 January 1996 to 31 December 2011
Temporal Resolution: Not specified
Data Format(s):
  • NetCDF
Platform(s) ALOS, ENVISAT, ERS-1, ERS-2, RADARSAT-1, RADARSAT-2
Sensor(s): ASAR, PALSAR, SAR
Version: V1
Data Contributor(s): Eric Rignot, Jeremie Mouginot, Bernd Scheuchl

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.

Rignot, E., J. Mouginot, and B. Scheuchl. 2011. MEaSUREs InSAR-Based Antarctica Ice Velocity Map, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/MEASURES/CRYOSPHERE/nsidc-0484.001. [Date Accessed].

Literature Citation

As a condition of using these data, we request that you acknowledge the author(s) of this data set by referencing the following peer-reviewed publication.

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Detailed Data Description

Format

Data are available in Network Common Data Form, Version 3 (NetCDF 3) format. For more information about working with NetCDF formatted data, visit the UCAR Unidata Network Common Data Form Web site.

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File and Directory Structure

Data are available on the HTTPS site in the https://n5eil01u.ecs.nsidc.org/MEASURES/NSIDC-0484.001/ directory.

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File Naming Convention

This section explains the file naming convention used for this data set. Two files are available:

antarctica_ice_velocity_450m.nc (450 m spacing)
antarctica_ice_velocity_900m.nc (900 m spacing)

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File Size

The 450 m velocity file is approximately 1.4 GB. The 900 m file is approximately 340 MB.

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Spatial Coverage

The data set spans the continent of Antarctica.

Southernmost Latitude: 90°S 
Northernmost Latitude: 60°S 
Westernmost Longitude: 180°W 
Easternmost Longitude: 180°E

Figure 1. Antarctic ice velocity derived from (A) PALSAR, (B) ASAR, (C) RADARSAT-2, and (D) RADARSAT-1 and ERS-1 and 2 satellite radar interferometry color coded on a logarithmic scale and overlaid on a MODIS mosaic of Antarctica. Projection is polar stereographic at 71°S secant plane. Thick black lines delineate major ice divides. 
(Rignot, Mouginot, and Scheuchl 2011)

Spatial Resolution

The velocity maps are provided at 450 m and 900 m spacings.

Projection 

Polar stereographic with true scale at 71° S.

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Temporal Coverage

The data used in this data set were collected between 1996 and 2011. Detailed information is provided in the Data Acquisition and Processing section. 

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Parameter or Variable

These maps provide velocity data for the Antarctic Ice Sheet at 450 m and 900 m spacings. Velocity information (meters per year) for the x and y direction, as defined by the polar stereographic grid, is stored in the NetCDF variables named vx and vy. Error estimates for the velocity magnitude are located in the variable err; however, these values should be used more as an indication of relative quality rather than absolute error. More information about the error estimates is provided in the Quality Assessment section as well as in Rignot, et al. 2011.

Variable Description

Each NetCDF file contains the variables listed in Table 1:

Table 1. Variable Description
Variable Description Dimensions Data Type
vx Velocity in m/year in x direction

450 m: 12445 x 12445

900 m: 6223 x 6223

float
vy Velocity in m/year in y direction

450 m: 12445 x 12445

900 m: 6223 x 6223

float
err Estimated error in velocity magnitude

450 m: 12445 x 12445

900 m: 6223 x 6223

byte (signed)

To convert the vx and vy velocity components into magnitude (speed) and direction (angle), use the following equations:

(1)   speed = √(vx2 + vy2)
(2)   angle = arctan (vy / vx)

However, users should take care when computing the inverse tangent due to the function's inherent ambiguities. While the standard arctan function typically does not account for angles which differ by 180°, most modern computer languages and math software packages include the function ATAN2, which uses the signs of both vector components to place the angle in the proper quadrant.

Sample Image

Figure 2. Antarctic ice velocity derived from ALOS PALSAR, Envisat ASAR, RADARSAT- 2 
and ERS-1/2 satellite radar interferometry color coded on a logarithmic scale.
(Rignot, Mouginot, and Scheuchl 2011

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Software and Tools

Software and Tools

Unidata at the University Corporation for Atmospheric Research maintains an extensive list of freely available Software for Manipulating or Displaying NetCDF Data.

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Volume
Data volume

450 m spacing: 1.36 GB
900 m spacing: 340 MB
Total volume: 1.70 GB

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Quality Assessment

A detailed description of these data and their quality is provided in Rignot, et al., 2011. The precision of ice flow mapping varies with the sensor, the geographic location, the technique of interferometric analysis (refer to Data Acquisition and Processing for details), the time period of analysis, the repeat cycle, and the amount of data stacking. The error estimates are summarized in Table 2. The error map in Figure 3 takes into account the following error sources:

  • Error of speckle tracking and interferometric phase analysis respectively
  • Errors caused by ionospheric perturbations (strongest in the azimuth direction, stronger in L-band compared to C-band, stronger in the East Antarctic Ice Sheet (EAIS) compared to the West Antarctic Ice Sheet (WAIS) because ionospheric perturbations are more abundant near the magnetic pole
  • Data stacking (reduces the error noise as the square root of the number of interferometric pairs averaged)
  • Respective weight of each instrument in the mosaicking

The total error is the square root of the sum of the independent errors squared. More details on the error estimates are provided in Rignot, et al., 2011 (supplementary online material). Table 2 provides the error in ice velocity mapping for each sensor, without data stacking, in range (Rg) and azimuth (Az).

Table 2. Error in Ice Velocity Mapping (m/yr)
Sensor Repeat Cycle
(day)
Pixel Size Speckle Tracking PhaseRg 
(m/yr)
IonosphereAz
(m/yr)
Total Error
(m/yr)
Rg (m) Az (m) Rg (m/yr) Az (m/yr)
ALOS (WAIS) 46 4.7 3.3 0.5 0.2 0.03 17 17
ALOS (EAIS) 46 4.7 3.3 0.5 0.2 0.03 8 8
ASAR 35 4.7 3.3 1.6 0.3 0.03 4.1 4
RADARSAT-2 24 11.8 5.3 2.1 0.6 0.021 5.9 6
RADARSAT-1 24 8.1 5.3 2.4 0.6 0.03 5.9 6
ERS-1 and -2 1 7.9 4.0 56 12 0.73 N/A 1
Figure 3. Velocity magnitude error on a linear scale color coded from 1 to greater than 16 m/yr. Thick black lines delineate major ice divides and the grounding line (Rignot, et al. 2011).

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Data Acquisition and Processing

Theory of Measurements

This data set provides ice velocity information for the entire Antarctic continent, derived from a variety of satellite radar interferometry data. Two techniques of interferometric analysis were used to generate the maps:

  1. Speckle tracking in both along (azimuth) and across (range) track directions
    Calculation of two dimensional offsets in amplitude imagery
  2. Combinations of (range) interferometric phases along two independent tracks
    Combination of interferometric phases of two independent tracks to retrieve the surface flow vector

In both cases, surface parallel flow is assumed, a conventional approach for ice sheets.

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Data Acquisition Methods

Ice velocity information for the Antarctic Ice Sheet was derived using satellite synthetic aperture radar interferometry (InSAR) data from spring 2009 data from the Canadian Space Agency (CSA)'s and MacDonald, Dettwiler and Associates Ltd. (MDA)'s RADARSAT-2, spring 2007-2008-2009 data from European Space Agency (ESA)'s Envisat Advanced Synthetic Aperture Radar (ASAR), and fall 2007-2008 data from the Japan Aerospace Exploration Agency (JAXA)'s Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR), complemented by patches of CSA's RADARSAT-1 data from fall 2000 and ESA's Earth Remote Sensing Satellites ERS-1 and -2 data from spring 1996. Each radar instrument contributes its unique coverage and performance level. The final mosaics assemble 900 satellite tracks and more than 3,000 orbits of radar data. Data acquisitions between 2006 and 2011 were coordinated through the IPY Space Task Group.

The 450 m map contains some minor improvements compared with the 900 m product, such as slightly better coverage in West Antarctica due to the inclusion of a few additional tracks and a tide correction for Ross and Ronne ice shelves (RADARSAT-2, 2009 tracks only). The Theory of Measurements section of the MEaSUREs InSAR-Based Ice Velocity Maps of Central Antarctica: 1997 and 2009 documentation contains additional details about this correction.

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Data Sources

Table 3 describes the data sources used in this data set.

Table 3. Temporal and spatial coverage of source satellite data
Platform Look Dir. Mode Repeat Cycle (day) Incidence Angle Resolution 
Rg x Az (m)
Swath (km) Frequency (GHz) # of Proc. Tracks Raw Data Volume Year
ERS-1 & 2 Right N/A 1-3 23 13x4 83 5.33 60 0.5 1996
RADARSAT-1 Left S2-S7 24 28-47 12x5-17x6 62 5.33 72 0.5 1997
Right various 24 18-38 7x5-12x5 62 5.33 84 0.5 2000
ENVISAT Right IS2 35 23 13x5 70 5.33 115/130/210 1/1/2 2007/2008/2009
RADARSAT-2 Left S5/EH4 24 41/57 12x5 70 5.33 135/14 4/1 2009/2011
ALOS PALSAR Right FBS 46 39 7x4 45 1.27 64/204/296 2/6/9 2006/2007/2008

Version History

Version 1.2 was released July, 2015. Refer to Table 4 for this data set's version history:

Table 4. Version History
Version Description
V1.2 Binary data file format discontinued. Data available in NetCDF only (August, 2015).
V1.1 Added a second mosaic at 450 m resolution (September, 2013)
V1 Initial version (October, 2011)
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References and Related Publications

Contacts and Acknowledgments

Investigators

Dr. Eric Rignot
University of California, Irvine 
Department of Earth System Science 
Croul Hall
Irvine, California 92697
USA

Dr. Jeremie Mouginot
University of California, Irvine 
Department of Earth System Science 
Croul Hall
Irvine, California 92697
USA

Dr. Bernd Scheuchl
University of California, Irvine 
Department of Earth System Science 
Croul Hall
Irvine, California 92697
USA

Acknowledgments: 

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

Spaceborne Synthetic Aperture Radar (SAR) acquisitions were provided through the following data grants:

  • ALOS PALSAR: Japan Aerospace Exploration Agency (JAXA)
  • ENVISAT ASAR, ERS-1, ERS-2: European Space Agency (ESA)
  • RADARSAT-1, RADARSAT-2: Canadian Space Agency (CSA)

Data acquisitions between 2006 and 2011 are courtesy of the International Polar Year (IPY) Space Task Group.

Document Information

DOCUMENT CREATION DATE

October 2011

DOCUMENT REVISION DATE

August 2015

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