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

Summary

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.

Data are available via FTP, provided in both ASCII text (.txt) and shapefile (.shp, .dbf, .shx) formats.

Citing These Data

The following example shows how to cite the use of this data set in a publication. For more information, see our Use and Copyright Web page.

The following example shows how to cite the use of this data set in a publication. List the principal investigators, year of data set release, data set title, publisher: NSIDC, and digital media.

Bindschadler, R., H. Choi, and ASAID Collaborators. 2011. High-resolution Image-derived Grounding and Hydrostatic Lines for the Antarctic Ice Sheet. Boulder, Colorado, USA: National Snow and Ice Data Center. Digital media.

The following published journal article provides comprehensive documentation for this data set:

Bindschadler, R., H. Choi, A. Wichlacz, R. Bingham, J. Bohlander, K. Brunt, H. Corr, R. Drews, H. Fricker, M. Hall, R. Hindmarsh, J. Kohler, L. Padman, W. Rack, G. Rotschky, S. Urbini, P. Vornberger, and N. Young. 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. doi:10.5194/tc-5-569-2011.

Overview Table

Category	Description
Data format	ASCII shapefile
Spatial coverage and resolution	Southernmost Latitude: 80°S Northernmost Latitude: 60°S Westernmost Longitude: 180°W Easternmost Longitude: 180°E
Temporal coverage	1999 to 2003
File naming convention	ASAID_GL_full.dbf ASAID_GL_final_full.txt ASAID_island_HL_Final.txt
File size	Files range in size from 1.42 MB to 1367 MB.
Parameter(s)	Grounding Line Hydrostatic Line
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

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

Technical Contact

2. 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.

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.

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.

File Size

Files range in size from 1.42 MB to 1367 MB.

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

Temporal Coverage

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

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. 1: Excellent 2: Semi-excellent 3: Medium 4: Somewhat poor 5: Poor
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

Note: NaN indicates non-number values.

Sample Data Record

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

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

Quality Assessment

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

3. Data Access and Tools

Data Access

Data are available via FTP.

Volume

Total volume of the data is 3665 MB.

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.

Related Data Collections

• ICESat-Derived Grounding Zone for Antarctic Ice Shelves
• Mosaic of Antarctica Image Map
• Radarsat Antarctic Mapping Project Digital Elevation Model Version 2

4. 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 I_b in the diagram, the slope break, because it is derived primarily from optical imagery and secondarily from derived surface elevations.

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

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.

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 principle 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.

5. References and Related Publications

Bindschadler, R., H. Choi, A. Wichlacz, R. Bingham, J. Bohlander, K. Brunt, H. Corr, R. Drews, H. Fricker, M. Hall, R. Hindmarsh, J. Kohler, L. Padman, W. Rack, G. Rotschky, S. Urbini, P. Vornberger, and N. Young. 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 Discussions, 5, 183-227. doi:10.5194/tcd-5-183-2011.

Bindschadler, R., P. Vornberger, A. Fleming, A. Fox, J. Mullins, D. Binnie, S. J. Paulsen, B. Granneman, and D. Gorodetzky. 2008. The Landsat Image Mosaic of Antarctica. Remote Sensing of the Environment. 112, 4214-4226. doi:10.1016/j.rse.2008.07.006

Bamber, J. L., J. L. Gomez-Dans, and J. A. Griggs. 2009. A New 1 km Digital Elevation Model of the Antarctic Derived from Combined Satellite Radar and Laser Data Part 1: Data and Methods. The Cryosphere, 3, 101-111.

Korona J., E. Berthier, M. Bernard, F. Remy, and E.Thouvenot. 2009. SPIRIT. SPOT 5 Stereoscopic Survey of Polar Ice: Reference Images and Topographies during the Fourth International Polar Year (2007-2009). ISPRS Journal of Photogrammetry and Remote Sensing, Vol. 64, p. 204-212.

Liu, H., K. Jezek, B. Li, and Z. Zhao. 2001. Radarsat Antarctic Mapping Project Digital Elevation Model Version 2. Boulder, CO: National Snow and Ice Data Center, Digital media.

Van den Broeke, M. R., W. J. van de Berg and E. van Meijgaard. 2008. Firn Depth Correction along the Antarctic Grounding Line, Antarctic Science, doi:10.1017/S095410200800148X.

The following related documents are available :

Table 5. Related Documents

Document	Description	URL
Antarctic Glaciological Data Center	Data Center Web site	http://nsidc.org/agdc/
ASAID: Antarctic Surface Accumulation and Ice Discharge	ASAID Project Description	http://ipy.arcticportal.org/projects/item/226-asaid-antarctic-surface-accumulation-and-ice-discharge

6. Document Information

Acronyms

The following acronyms are used in this document.

Table 6. Acronyms and Abbreviations

Acronym	Description
ASAID	Antarctic Surface Accumulation and Ice Discharge
ASTER	Advanced Spaceborne Thermal Emission and Reflection Radiometer
DEM	Digital Elevation Model
FTP	File Transfer Protocol
GL	Groundling Line
HL	Hydrostatic Line
ICESat	Ice, Cloud, and land Elevation Satellite
NSIDC	National Snow and Ice Data Center
SPIRIT	SPOT 5 Stereoscopic Survey of Polar Ice: Reference Images and Topographies
URL	Uniform Resource Locator

Document Creation Date

21 April 2011

Document URL

http://nsidc.org/data/docs/agdc/nsidc0489_bindschadler/index.html