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Data Set ID:
NSIDC-0075

GEOSAT Radar Altimeter DEM Atlas of Antarctica North of 72.1 degrees South, Version 1

The Antarctic atlas consists of 28 digital elevation maps which cover
all of Antarctica north of 72.1 degrees south at a resolution of
three kilometers. Each map contains surface elevations and
coordinates for one atlas page covering 16 degrees of longitude. Data
were acquired by the Geodetic Satellite (GEOSAT) Geodetic Mission
(GM) from March 1985 through September 1986 and are available in both
Universal Transverse Mercator (UTM) coordinates, and in latitude and longitude coordinates.

Data were mapped using the UTM projection in atlas form to decrease
the distortion that usually occurs at the poles. Many features of the
Antarctic Ice Sheet are shown in more detail than in previous digital elevation models, especially along the margin of the East Antarctic
Ice Sheet. A geostatistical mapping technique (Herzfeld et al. 1993)
improved the accuracy of surface elevations compared to previous
GEOSAT elevation data sets. This atlas will facilitate the monitoring
of changes in surface elevation that could indicate mass changes in
the Antarctic Ice Sheet.

Geographic Coverage

Parameter(s):
  • Topography > Contours
  • Glaciers/Ice Sheets > Glacier Elevation/Ice Sheet Elevation
  • Glaciers/Ice Sheets > Glaciers
  • Glaciers/Ice Sheets > Glacier Topography/Ice Sheet Topography
  • Glaciers/Ice Sheets > Ice Sheets
  • Topography > Landforms
  • Topography > Surface Roughness
  • Topography > Terrain Elevation
Spatial Coverage:
  • N: -65, S: -72, E: 180, W: -180

Spatial Resolution: Not Specified
Temporal Coverage:
  • 1 April 1985 to 30 September 1986
Temporal Resolution: Not specified
Data Format(s):
  • ASCII Text
Platform(s) GEOSAT
Sensor(s): RADAR ALTIMETERS
Version: V1
Data Contributor(s): Ute Herzfeld
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.

Ute Christina Herzfeld, Michael S. Matassa 1999. GEOSAT Radar Altimeter DEM Atlas of Antarctica North of 72.1 degrees South, Version 1. [Indicate subset used]. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi: http://dx.doi.org/10.5067/8SH7MO0Z9589. [Date Accessed].

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Data Set Overview

>63 to 68 deg. S 97 to 113 deg E

>67 to 72 deg S. 73 to 89 deg E.

>67 to 72 deg S. 97 to 113 deg E

>67 to 72 deg S. 109 to 125 deg E.

>63 to 68 degrees south
97 to 113 degrees east
>67 to 72 degrees south
73 to 89 degrees east
>67 to 72 degrees south
97 to 113 degrees east
>67 to 72 degrees south
109 to 125 degrees east

Discussion

Although the importance of Antarctica in the global system has long been recognized and discussed in the literature, data as basic as topographic maps of a resolution amenable to geophysical analysis are still lacking for large parts of Antarctica. This investigation adds to the knowledge of Antarctica by using the improved evaluation of satellite altimetry from the GEOSAT Geodetic Mission to build a more accurate atlas of Antarctica north of 72.1 degrees south.

The following samples are visual representations of several map pages. Click on the thumbnail version to view the full-sized map page.

Refer to the Data Format section for more detailed information on how files are stored.

Detailed Data Description

The quality and detail of the maps in this data set makes them particularly useful to scientists for:

documenting more ice margin details.
showing ice drainage areas and troughs.
identifying ice shelves.
studying ice dynamics and changes in Antarctic ice-stream and ice-shelf systems.
correcting satellite images for effects of slope and elevation.

The kriging method used in producing this atlas would also be applicable to future altimetry data and therefore will facilitate monitoring the changes in the ice streams and ice-surface elevation that are critical for a determination of mass balance and stability of the Antarctic Ice Sheet.

Format

The data for the UTM coordinates are stored a file called dtm.tar, which contains 28 files compressed by the UNIX gzip compression utility. Each file is named for the map area it covers. For example, the file named "m69e61_77n67_721.g.dtm.gz" contains data for the map area with central meridian of 69 degrees bounded east-west between 61.0 and 77.0 degrees and bounded north-south between -67.0 and -72.1 degrees.

The files are in ASCII format and contain the following 3 tab-delimited columns:

1 E-W UTM coordinate
2 N-S UTM coordinate
3 elevation value for grid node defined by columns 1 and 2

The data for latitude and longitude coordinates are stored in a file called dtm-11.tar. The files are in ASCII format and contain the following 3 tab-delimited columns:

1 Latitude
2 Longitude
3 elevation value for grid node defined by Columns 1 and 2


Grid Description

For the atlas, the Antarctic is divided into rows of map sheets (72.1 degrees to 67 degrees south; 68 degrees to 63 degrees south).

Map Sheet Parameters

Row (degrees) East Min. (UTM) East Max. (UTM) North Min. (UTM) North Max. (UTM) No. of grid nodes E-W No. of grid nodes N-S Map Size (km) E-W Map Size (km) N-S
67 - 72.1 227000 773000 -7998000 -7455000 183 182 546 543
63 - 68 167000 833000 -7542000 -7011000 223 178 666 531

Each of the 28 maps covers 16 degrees of longitude and overlaps two degrees with the maps on either side, so each map center is offset from the next one by 12 degrees of longitude. The map names (e.g., m69e61-77n721-67) give central meridian (69 degrees) and extent of the nominal map area (61 degrees to 77 degrees east, 72.1 degrees to 67 degrees). All the maps use the same projection with respect to the central meridian, and maps in the same row are the same size. For Antarctica, east coordinates always have six digits, while north coordinates have seven.

The files for the UTM coordinates are stored in the the dtm.tar file which expands to the dtm directory. The files for the latitude and longitude coordinates are stored in the dtm-ll.tar file which expands to the dtm-ll directory.

Atlas Maps by Name and Coordinates

The 28 Antarctic Atlas Maps are listed below with the coordinates and name of each map.

Coordinates  Map Name 
Central Meridian East Coordinates South Coordinates
45 37 to 53 63 to 68 Casey Bay
57 49 to 65 63 to 68 Napier Mountains
69 61 to 77 63 to 68 Mawson Coast East
81 73 to 89 63 to 68 Leopold and Astrid Coast
93 85 to 101 63 to 68 Queen Mary Coast
105 97 to 113 63 to 68 Knox Coast
117 109 to 125 63 to 68 Sabrina Coast
129 121 to 137 63 to 68 Claire Coast
141 133 to 149 63 to 68 Adelie Coast
153 145 to 161 63 to 68 Ninnis Glacier Tongue
297  289 to 305  63 to 68 Antarctic Peninsula (Graham Land)
15W 23W to 7W 67 to 72.1 Ekstrom Ice Shelf
3W 11W to 5 67 to 72.1 Fimbul Ice Shelf
9 1 to 17 67 to 72.1 Princess Astrid Coast
21 13 to 29 67 to 72.1 Erskine Iceport
33 25 to 41 67 to 72.1 Riiser-Larsen Peninsula
45 37 to 53 67 to 72.1 Prince Olav Coast
57 49 to 65 67 to 72.1 Mawson Coast West
69 61 to 77 67 to 72.1 Lambert Glacier
81 73 to 89 67 to 72.1 Ingrid Christensen Coast
93 85 to 101 67 to 72.1 Wilkes Land e85to101
105 97 to 113 67 to 72.1 Wilkes Land e97to113
117 109 to 125 67 to 72.1 Wilkes Land e109to125
129 121 to 137 67 to 72.1 Wilkes Land e121to137
141 133 to 149 67 to 72.1 Wilkes Land e133to149
153 145 to 161 67 to 72.1 Cook Ice Shelf
165 157 to 173 67 to 72.1 Pennell Coast
292 284 to 300 67 to 72.1 Antarctic Peninsula (Palmer Land)

Data Source

The data originate from the GEOSAT Geodetic Mission. Refer to the radar altimeter document for more information about the instrument.

Data Granularity

A general description of data granularity as it applies to the IMS appears in the EOSDIS Glossary. The data granularity for this data set is one map for every 16 degrees of longitude.

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File Size

Data File Size (in compressed tar file format):

File with UTM coordinates 
(dtm.tar.gz)
     8.0   MB
File with latitude and longitude coordinates 
(dtm-ll.tar.gz)
   11.68 MB
 

Unit of Measurement

UTM coordinates - meters [m]

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Spatial Coverage

This data set covers all of Antarctica from 60 degrees south to 72.1 degrees south at a resolution of three kilometers.

Projection 

The data were mapped using the Universal Transverse Mercator (UTM) Projection (Snyder, 1987). Data are stored as UTM coordinates and as latitude and longitude coordinates. The southern hemisphere UTM coordinates are negative numbers.

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Temporal Coverage

The data points for this data set were collected by the radar altimeter on the GEOSAT satellite from March, 1985 to September, 1986.

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Parameter or Variable

Sample Data Record

UTM version:
1 E-W UTM coordinate
2 N-S UTM coordinate
3 elevation value for grid node defined by columns 1 and 2
     233000.   -7.05900E+06   -1.30000   
     239000.   -7.05900E+06   -1.83622   
     242000.   -7.05900E+06   -1.97845   
     245000.   -7.05900E+06   -2.11752   
     248000.   -7.05900E+06   -2.11752   
     251000.   -7.05900E+06   -2.25113   
     254000.   -7.05900E+06   -2.33926   
     257000.   -7.05900E+06   -2.34469   
     260000.   -7.05900E+06   -2.64000   
     200000.   -7.06200E+06   -1.16000   
	 

Latitude/Longitude version:

1 Latitude
2 Longitude
3 elevation value for grid node defined by columns 1 and 2
  -63.559808       99.621068   -1.30000  
  -63.564277       99.741325   -1.83622  
  -63.566474       99.801469   -1.97845   
  -63.568646       99.861624   -2.11752   
  -63.570793       99.921789   -2.11752   
  -63.572914       99.981964   -2.25113   
  -63.575010      100.042149   -2.33926   
  -63.577081      100.102343   -2.34469   
  -63.579127      100.162548   -2.64000  
  -63.560204       98.954757   -1.16000   
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Software and Tools

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Data Acquisition and Processing

Theory of Measurements

Please see the section on Data Manipulations for more information on how data were processed.

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Data Acquisition Methods

The data were collected during the GEOSAT Geodetic Mission by a radar altimeter.

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Derivation Techniques and Algorithms

Satellite radar altimeters measure the time it takes an electromagnetic signal to travel from the altimeter antenna to the ice sheet surface and back to the altimeter's receiver. This "range measurement" allows investigators to determine the satellite's height above the ice sheet. NSIDC's Radar Altimeter document describes the instrument and how it works.

Corrections are applied to the range measurements to account for the fact that returns are different over ice than over the ocean. The correction for interpreting the data over ice is called "retracking," and is described in papers by Davis and Zwally (1993), and Zwally, et al. (1983).

Over sloping terrain, the radar altimeter measurement needs to be corrected because the return comes from a point not directly below the satellite, but to the uphill side. The elevation indicated by the return time in this case is higher than that directly below the satellite. The data are slope-corrected to reduce the errors, using the slope correction algorithm from Brenner et al. (1983).

For this data set, elevations were derived from the slope-corrected data and grid values were calculated using a geostatistical technique (Herzfeld et al. 1993) and individual atlas pages were created using UTM coordinates. The Universal Transverse Mercator (UTM) Projection (Snyder 1987) compensates for the distortion of areas far away from the central meridian.

After the UTM coordinates were calculated, the data were gridded using ordinary kriging with search algorithms developed for geographical track-line data (Herzfeld et al. 1993 and Journel and Huijbregts 1978). The particular kriging algorithm used for this data are described in Herzfeld (1990).

Map sheets were overlapped by two degrees to ensure that each point of Antarctica is contained in at least one map.

The UTM coordinates were converted to latitude and longitude coordinates after the data was gridded.

Error Sources

The maps are not accurate in mountainous terrain but are sufficiently accurate to determine surroundings and general shape of small glaciers.

Limitations of the Data

Orbital coverage of the GEOSAT Geodetic Mission did not extend to the poles.

Known Problems with the Data

Some offshore contours are caused by ice shelves and ice islands. Contour lines that resemble ground-track patterns may be artifacts, or may occur when there is over-representation of isolated higher elevations in regions of generally low relief, such as islands or larger ice bergs in the sea.

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References and Related Publications

Contacts and Acknowledgments

Investigator

Ute Christina Herzfeld

Geomathematik, Fachereich 
Geographie/Geowissenschaften, 
fachbereich 6 Universitaet Trier, 
D-54286 Trier, Germany
OR
Institute of Arctic and Alpine 
Research (INSTAAR) 
University of Colorado, 
Boulder, CO 80309-0450, USA

Document Information

DOCUMENT REVISION DATE

July, 1999

DOCUMENT REVIEW DATE

June, 1999

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