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What's hot in the news around climate and sea ice and what are scientists talking about now? 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.
Data Set ID:
NSIDC-0484
MEaSUREs InSAR-Based Antarctica Ice Velocity Map, Version 2
This data set, 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. Data were largely acquired during the International Polar Years 2007 to 2009, as well as between 2013 and 2016. Additional data acquired between 1996 and 2016 were used as needed to maximize coverage.
See Antarctic Ice Sheet Velocity and Mapping Data for related data.
This is the most recent version of these data.
Version Summary:
Version 2 includes data acquired from 2011-2016 from RADARSAT-2, Sentinel-1, TerraSAR-X (TSX), and TanDEM-X (TDX). Landsat-8 optical imagery also was integrated into the data to improve coverage. The mosaicking method was updated to make best use of the large number of scenes used for the mosaic. In addition, several new parameters are included for assessing the quality of the data including: the standard deviation of vx and vy for each pixel and count of scenes used for each pixel.
In version 2, coverage increased from 95.1% to 99.6% and a reduction in error was achieved due to the utilization of more data.
STANDARD Level of Service
Data: Data integrity and usability verified
Documentation: Key metadata and user guide available
User Support: Assistance with data access and usage; guidance on use of data in tools
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Geographic Coverage |
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Once you have logged in, you will be able to click and download files via a Web browser. There are also options for downloading via a command line or client. For more detailed instructions, please see Options Available for Bulk Downloading Data from HTTPS with Earthdata Login. Earthdata Search: This application allows you to search, visualize, and access data across thousands of Earth science data sets. Additional customization services are available for select data sets, including subsetting, reformatting, and reprojection. |
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. 2017. MEaSUREs InSAR-Based Antarctica Ice Velocity Map, Version 2. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/D7GK8F5J8M8R. [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.
Rignot, E., J. Mouginot, and B. Scheuchl. 2011. Ice Flow of the Antarctic Ice Sheet, Science. 333. 1427-1430. https://doi.org/10.1126/science.1208336
Mouginot, J., B. Scheuchl, and E. Rignot. 2012. Mapping of Ice Motion in Antarctica Using Synthetic-Aperture Radar Data, Remote Sensing. 4. 2753-2767. https://doi.org/10.3390/rs4092753
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Detailed Data Description
Format
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File and Directory Structure
Data are available on the HTTPS site in the https://n5eil01u.ecs.nsidc.org/MEASURES/NSIDC-0484.002/ directory in one folder, 1996.01.01/. In this folder, there is one file: antarctica_ice_velocity_450m_v2.nc.
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File Naming Convention
This data set includes one file named antarctica_ice_velocity_450m_v2.nc (450 m grid spacing).
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File Size
The size of this data set is approximately 4 GB.
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Spatial Coverage
The data set spans the continent of Antarctica. Figure 1 provides a map of the spatial coverage.
Southernmost Latitude: 90° S
Northernmost Latitude: 60° S
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
Spatial Coverage Map
Spatial Resolution
The spatial resolution of the velocity map is 450 m.
Projection
Polar stereographic with true scale at 71° S. Refer to Polar Stereographic Projection and Grid page for more information and polar stereographic grid definitions.
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Temporal Coverage
The data were collected between 1996 and 2016. Detailed information is provided in the Data Acquisition and Processing section.
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Parameter or Variable
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 VX and VY and are recorded in m/yr. Error estimates for the velocity components are provided as variables ERRX and ERRY; 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. The data also include the standard deviations for the velocity estimates (STDX,STDY), as well as a count of scenes (CNT) used to estimate the values for each pixel. Figure 2 shows the error and standard deviation estimates, and Figure 3 shows the total number of measurements used to estimate the velocity. Figure 4 shows a sample image of the data as a whole. Table 1 provides a complete list of the variables and their descriptions.
Variable Description
The variables included in the NetCDF file are described in Table 1. All variables have grid dimensions of 12445 x 12445 and are posted at 450 m spacing.
| Variable | Description | Data Type |
|---|---|---|
VX |
Component of velocity in m/yr in x direction | float |
VY |
Component of velocity in m/yr in y direction | float |
ERRX |
Estimated error in m/yr in x direction | float |
ERRY |
Estimated error in m/yr in y direction | float |
STDX |
Standard deviation of vx |
float |
STDY |
Standard deviation of vy |
float |
CNT |
Count of scenes used per pixel | integer |
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)
(3) error = √(errx2 + erry2)
(4) error of flow direction = error/(2*speed) (see Mouginot et al., 2012)
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 that 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
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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.
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 2 takes into account the following error sources:
- Error of speckle tracking and interferometric phase analysis respectively (SAR only)
- 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
- Error of feature tracking analysis (Landsat-8 only)
- 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 Mouginot, et al., 2017. Table 2 provides the error in ice velocity mapping for each sensor, without data stacking, in range (Rg) and azimuth (Az).
| Platform/Sensor | Nominal Repeat Cycle (day) |
Error (m/yr) | |
|---|---|---|---|
| Rg | Az | ||
| ALOS (WAIS)/PALSAR | 46 | 6 | 17 |
| ALOS (EAIS)/PALSAR | 46 | 6 | 5 |
| ENVISAT/ASAR | 35 | 21 | 4 |
| RADARSAT-2/SAR | 24 | 26 | 8 |
| RADARSAT-1/SAR | 24 | 26 | 8 |
| Sentinel-1/SAR | 12 | 12 | 43 |
| Landsat-8/OLI | 16 | 34* | 34* |
| TanDEM-X (TDX)/TerraSAR-X (TSX)/SAR | 11 | 8 | 8 |
| Tandem ERS-1 and -2 (phase)/SAR | 1 | 1 | N/A |
*Landsat uses repeat image feature tracking in x and y
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Data Acquisition and Processing
Theory of Measurements
This data set provides a comprehensive ice velocity map for the entire Antarctic ice sheet, derived from a variety of satellite radar interferometry data. (See the Data Sources section for a complete list.) Several analysis techniques using SAR data were used to generate the maps:
- Speckle tracking in both along (azimuth) and across (range) track directions
- Calculation of two dimensional offsets in amplitude imagery
- Combinations of (range) interferometric phases along two independent tracks
- Combination of interferometric phases of two independent tracks to retrieve the surface flow vector
In all cases, surface parallel flow is assumed, a conventional approach for ice sheets. The Landsat-8 data are processed using repeat image feature tracking (see Mouginot, et al. 2017).
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Data Acquisition Methods
This digital image mosaic was built from the sources listed in Table 3, as well as the following:
- The RADARSAT-2 data acquired during spring 2009 was augmented by a 2011 gap-filling campaign
- Envisat Advanced Synthetic Aperture Radar (ASAR) data acquired during spring 2007, 2008, and 2009
- Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) data acquired during fall 2007-2008
The Version 2.0 mosaic also uses RADARSAT-2 (CSA) (2012-2016) and Sentinel-1 (Copernicus/ESA/EU) (2014-2016) data, Landsat-8 data acquired between 2013 and 2016, TanDEM-X and TerraSAR-X (DLR) between 2011 and 2014, and additional PALSAR (ALOS/JAXA) between 2006 and 2010. SAR acquisitions between 2006 and 2016 were coordinated by the IPY Space Task Group and its successor, the Polar Space Task Group (PSTG).
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Data Sources
Table 3 describes the data sources used in this data set.
| Platform/Sensor | Space Agency | Look Dir. | Mode | Repeat Cycle (day) |
Incidence Angle | Resolution Rg x Az (m) |
Frequency (GHz) | Year |
|---|---|---|---|---|---|---|---|---|
| ERS-1 & 2/SAR | European Space Agency (ESA) | Right | N/A | 1-3 | 23 | 13x4 | 5.33 | 1996 |
| RADARSAT-1/SAR | Canadian Space Agency (CSA) | Left/Right | Varies | 24 | 18-47 | 12x5-17x6 | 5.33 | 1997/2000 |
| ENVISAT/ASAR | ESA | Right | IS2 | 35 | 23 | 13x5 | 5.33 | 2007-2009 |
| RADARSAT-2/SAR | CSA | Left | S5/EH4 | 24 | 41/57 | 12x5 | 5.33 | 2009-2016 |
| ALOS/PALSAR | Japan Aerospace Exploration Agency (JAXA) | Right | FBS | 46 | 39 | 7x4 | 1.27 | 2006-2010 |
| Sentinel-1/SAR | ESA | Right | IW-T OPS | 12 | 12x43 | 5.33 | 2014-2016 | |
| Landsat-8/OLI | USGS/NASA | N/A | Panchromatic | 16 | N/A | 15x15 | 2013-2016 | |
| TanDEM-X/TerraSAR-X/SAR | German Space Agency (DLR) | right | N/A | 11 | 46.3 | 1.4x1.8 | 9.65 | 2011-2016 |
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Version History
Version 2.0 was released April 2017. Refer to Table 4 for this data set's version history:
| Version | Description |
|---|---|
| V2.0 | Added post 2011 SAR data (RADARSAT-2, Sentinel-1, TanDEM-X/TerraSAR-X) and Landsat-8 optical data (March 2017). The mosaicking method was updated to make best use of the large number of scenes used for the mosaic. New quality parameters including the standard deviation and count variables are provided in the NetCDF file. |
| 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 agencies:
ALOS PALSAR: Japan Aerospace Exploration Agency (JAXA)
ENVISAT ASAR, ERS-1, ERS-2: European Space Agency (ESA)
Sentinel-1: Copernicus/ESA
RADARSAT-1, RADARSAT-2: Canadian Space Agency (CSA)
Landsat-8 (optical) data were made available by United States Geological Survey (USGS).
Data acquisitions between 2006 and 2016 are courtesy of the International Polar Year (IPY) Space Task Group and its successor, the Polar Space Task Group (PSTG).
Contains modified Copernicus Sentinel data (2014-2016), acquired by the European Space Agency, distributed through the Alaska Satellite Facility, and processed by Rignot, E., J. Mouginot, and B. Scheuchl.
Document Information
DOCUMENT CREATION DATE
April 2017
DOCUMENT REVISION DATE
No technical references available for this data set.
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