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Data Set ID:
NSIDC-0489

High-resolution Image-derived Grounding and Hydrostatic Lines for the Antarctic Ice Sheet, Version 1

This data set provides grounding line and hydrostatic line locations for the Antarctic coastline and islands around Antarctica. The data are derived using customized software to combine data from Landsat-7 imagery and Ice, Cloud, and land Elevation Satellite (ICESat) laser altimetry, which were primarily collected between 1999 to 2003. The data set also includes elevations along each line, selected from six candidate digital elevation models. The data were developed as part of the Antarctic Surface Accumulation and Ice Discharge (ASAID) project.

Geographic Coverage

Spatial Coverage:
  • N: -60, S: -80, E: 180, W: -180

Spatial Resolution: Not Specified
Temporal Coverage:
  • 1 January 1999 to 31 December 2003
Temporal Resolution: Not specified
Parameter(s):
  • Glaciers/Ice Sheets > Glaciers
  • Glaciers/Ice Sheets
  • Glaciers/Ice Sheets > Ice Sheets
Platform(s) ICESAT, LANDSAT-7, RADARSAT-2, SPOT-5
Sensor(s): ETM+, GLAS, SAR
Data Format(s):
  • ESRI Shapefile
  • ASCII Text
Version: V1
Data Contributor(s): Robert Bindschadler, Hyeungu Choi

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.

Bindschadler, R., H. Choi, and ASAID Collaborators. 2011. High-resolution Image-derived Grounding and Hydrostatic Lines for the Antarctic Ice Sheet, Version 1. [Indicate subset used]. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi: http://dx.doi.org/10.7265/N56T0JK2. [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.

  • Bindschadler, R. et al. 2011. Getting around Antarctica: New High-Resolution Mappings of the Grounded and Freely-Floating Boundaries of the Antarctic Ice Sheet Created for the International Polar Year, The Cryosphere. 5. 569-588. http://dx.doi.org/10.5194/tc-5-569-2011

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Detailed Data Description

Format

Data are provided in ASCII text (.txt) format, and as shapefiles (.shp, .dbf, .shx). The shapefiles contain only the latitude, longitude, Map X, Map Y, and confidence parameters from the text files.

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File and Directory Structure

Data are available on the FTP site in the ftp://sidads.colorado.edu/pub/DATASETS/AGDC/nsidc0489_bindschadler_V01/ directory. Within this directory, there are 16 data files as described in Table 1.

Table 1. File Description
Filename Description
ASAID_continent_GL.txt Text file containing the continental grounding line positions.
ASAID_continent_GL.dbf
ASAID_continent_GL.shp
ASAID_continent_GL.shx
Shapefiles for the continental grounding line position.
ASAID_continent_HL.txt Text file containing the continental hydrostatic line positions.
ASAID_continent_HL.dbf
ASAID_continent_HL.shp
ASAID_continent_HL.shx
Shapefiles containing the continental hydrostatic line position.
ASAID_island_GL.txt Text file containing the grounding line position for islands around Antarctica.
ASAID_island_GL.dbf
ASAID_island_GL.shp
ASAID_island_GL.shx
Shapefiles for the grounding line position for islands around Antarctica.
ASAID_island_HL.txt Text file containing the hydrostatic line position for islands around Antarctica.
ASAID_island_HL.dbf
ASAID_island_HL.shp
ASAID_island_HL.shx
Shapefiles containing the hydrostatic line position for islands around Antarctica.
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File Naming Convention

Files are named according to the following convention and as described in Table 2:

ASAID_Type_NL.ext

Where:

Table 2. File Naming Convention
Variable Description
ASAID Project Name
Type Continent: Coast of continental Antarctica
Island: Coastlines of islands surrounding Antarctica
NL GL: Grounding Line
HL: Hydrostatic Line
.ext File Extension:
.txt: Text file
.dbf, .shp, .shx: Shapefiles

Example: ASAID_island_HL.txt provides the hydrostatic line positions for islands around Antarctica, in ASCII text (.txt) format.

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File Size

Files range in size from 1.42 MB to 1367 MB.

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Spatial Coverage

This data set covers the coastline and islands around Antarctica.

Southernmost Latitude: 80°S 
Northernmost Latitude: 60°S 
Westernmost Longitude: 180°W 
Easternmost Longitude: 180°E

Projection

Polar Stereographic Projection Information:
Datum: WGS-84
SEMIMAJOR_AXIS=6378137.0, 
SEMIMINOR_AXIS=6356752.314
CENTER_LONGITUDE=0
CENTER_LATITUDE=-71
FALSE_EASTING=0.0
FALSE_NORTHING=0.0

Grid Description

Polar Stereographic, 15 meter spacing

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Temporal Coverage

The data set is based on satellite data collected from 1999 to 2003.

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Parameter or Variable

Text files contain detailed coordinates for the grounding and hydrostatic lines, including elevation measurements from a variety of DEMs and satellite data used to define the lines.

Shapefiles contain only the latitude, longitude, and polar stereo graphic coordinates of points in the hydrostatic and grounding line, along with confidence intervals for each point.

Parameter Description

Table 3. Parameter Description for the Grounding Line (GL) and Hydrostatic Line (HL) files
Parameter Description
Map X, Map Y Polar stereographic projection map grid position of the grounding line or hydrostatic line point in meters.
Latitude, Longitude Latitude and longitude position of the grounding line or hydrostatic line point.
Photoclinometry Elevation (referenced to EGM96 geoid) extracted from photoclinometry Digital Elevation Model (DEM) at grounding line or hydrostatic line position in meters.
Triangulation Elevation (referenced to EGM96 geoid) extracted from triangulation DEM at grounding line or hydrostatic line position in meters.
RAMP Elevation (referenced to EGM96 geoid) extracted from bilinear interpolation of Radarsat Antarctic Mapping Project (RAMP) DEM at grounding line or hydrostatic line position in meters.
Bamber Elevation (referenced to EGM96 geoid) extracted from bilinear interpolation of Bamber et. al. DEM at grounding line (or hydrostatic line) position, in meters.
ASTER Elevation (referenced to EGM96 geoid) extracted from bilinear interpolation of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) DEM at grounding line (or hydrostatic line) position, in meters. See http://www.ersdac.or.jp/GDEM/E/index.html for more details.
GLAS ICESat Geoscience Laser Altimeter System (GLAS) elevation values (referenced to EGM96 geoid) within 4 meters (horizontally) of grounding line (or hydrostatic line) position, in meters.
Chosen_Elev The best elevation value, in meters, chosen from five above DEMs (Photoclinometry, Triangulation, Ramp, Bamber, ASTER).
Transition Geophysical transition type flag at the grounding line or hydrostatic line position. 
1: Ice shelf 
2: Outlet glacier
3: Fast ice 
4: Open ocean
5: Rock
Confidence Confidence of chosen elevation at the grounding line or hydrostatic line position. 
0: Not evaluated for confidence 
1: Excellent
2: Semi-excellent
3: Medium
4: Somewhat poor
5: Poor
Note: The 0 value exists only in the island grounding line file. Use the values of the neighboring points when assessing the confidence values marked as 0. There were no confidence values found to be Poor (indicated as 5) in the hydrostatic or grounding line files for the island coastlines.
SPIRIT Elevation (referenced to EGM96 geoid) extracted from bilinear interpolation of available SPOT 5 Stereoscopic Survey of Polar Ice: Reference Images and Topographies (SPIRIT) DEM at grounding line or hydrostatic line position. For more information see Korona, et. al.
Firn_Correction Calculated firn depth correction value at the grounding line or hydrostatic line position defined as the difference between the combined ice/firn column thickness and the equivalent ice thickness. Values are bilinearly interpolated from van den Broeke, M. R.., et. al.
Ice_thickness (Hydrostatic line only) Ice thickness values, in meters, at the hydrostatic line position calculated from surface elevation, firn correction and ice flotation criterion.
Segment_Flag (Hydrostatic line only) Flags for beginning and ending of a segment of the hydrostatic line required because the hydrostatic line is discontinuous.
1: Begin 
2: End


 

Sample Data Record

Note 1: NaN indicates non-number values.

Note 2: Wide variations in elevation values, including negative elevation values occasionally occur because of limitations in the DEMs.

Map X

Map Y

Latitude

Longitude

Photoclinometry

Triangulation

Ramp

Bamber

ASTER

GLAS

Chosen_Elev

Transition

Confidence

SPIRIT

Firn_Correction

1996695

-1687980

-66.267746

130.21075

0

39.87571

0.61582565

-962.38416

34.385498

NaN

0.615256

3

4

NaN

15.04321

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Software and Tools

An ASAID software package used to define the grounding and hydrostatic lines is also available upon request. The software package is available as an IDL file, and a user manual is available in Microsoft Word format. To request the software, contact NSIDC User Services.

Quality Assessment

ASAID participants provided additional data to validate ASAID products. Detailed description of the validation process is available in Bindschadler, et. al., 2011.

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Data Acquisition and Processing

Theory of Measurements

This data set provides positions of the Grounding Line (GL) and Hydrostatic Line (HL) for the Antarctic Ice Sheet and surrounding islands. The GL is defined as the point where the ice in contact with the bedrock floats free of the ground. The HL is defined as the point where recently ungrounded ice first begins to float freely.

Figure 1 shows the anatomy of the grounding zone, the region where the ice shet moves from land into water. The ASAID grounding line is most consistent with point Ib in the diagram, the slope break, because it is derived primarily from optical imagery and secondarily from derived surface elevations.

schematic diagram of grounding zone
Figure 1. Anatomy of a Grounding Zone (from Fricker, et. al., 2009)

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Data Source

This data set was derived primarily from images from the Landsat-7 Enhanced Thematic Mapper Plus (ETM+), specifically, the image data set selected for teh Landsat Image Mosaic of Antarctica (LIMA; Bindschadler, et. al., 2008), and elevation profiles from the Ice, Cloud, and land Elevation Satellite (ICESat) Geoscience Laser Altimeter System (GLAS), from 1999 to 2003. Additional DEMs were used for elevation data.

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Derivation Techniques and Algorithms

Derivation of the grounding and hydrostatic line positions utilized the ASAID software package, which available along with a user manual upon request from NSIDC User Services. ASAID participants each mapped a segment of the grounding line and produced photoclinometric elevation fields for that segment. The principal investigator, Robert Bindschadler, produced the hydrostatic line and elevation data, and reviewed all the data products. The ASAID team produced sections of the hydrostatic line using the ASAID software package.

A detailed description of methods is available in Bindschadler, et. al., 2011.

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References and Related Publications

Contacts and Acknowledgments

Investigators

Dr. Robert Bindschadler
NASA Goddard Space Flight Center 
Mail Code 971 
Greenbelt, MD 20771
USA

Hyeungu Choi
SAIC
4600 Powder Mill Road, Suite 4000, 
Beltsville, MD 20705
USA

Document Information

Document Creation Date

21 April 2011

No technical references available for this data set.
No FAQs or How Tos available for this data set.

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Questions? Please contact:
NSIDC User Services
Phone: 1 303 492-6199
Email: nsidc@nsidc.org