Data Set ID:

Subglacial water flow paths under Thwaites Glacier, West Antarctica, Version 1

This data set contains subglacial water flow paths beneath Thwaites Glacier, West Antarctica, interpreted from ice thickness and bed elevation measurements collected between 7 December 2004 and 31 January 2005 by the Airborne Geophysical Survey of the Amundsen Embayment (AGASEA) expedition.

NSIDC does not archive these data.

  • Glaciers/Ice Sheets > Glacier Elevation/Ice Sheet Elevation > GLACIER ELEVATION/ICE SHEET ELEVATION
  • Glaciers/Ice Sheets > Glacier Thickness/Ice Sheet Thickness > GLACIER THICKNESS/ICE SHEET THICKNESS
  • Glaciers/Ice Sheets > Glacier Topography/Ice Sheet Topography > GLACIER TOPOGRAPHY/ICE SHEET TOPOGRAPHY
Data Format(s):
  • PDF
Spatial Coverage:
N: -75, 
S: -80, 
E: -90, 
W: -120
Spatial Resolution:Not SpecifiedSensor(s):RADAR
Temporal Coverage:
  • 7 December 2004 to 31 January 2005
Temporal ResolutionNot specifiedMetadata XML:View Metadata Record
Data Contributor(s):Sasha Carter, Duncan Young, Donald Blankenship

Geographic Coverage

Please contact the data provider for the correct Data Citation for this data set.

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Detailed Data Description


Data are provided as an ASCII text file with a corresponding .pdf map.

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File and Directory Structure

The FTP directory contains two files:

  •, an ASCII text file that contains the flow path data;
  •, a Portable Document Format file that contains a map of the flow paths.
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File Size and are 48 KB and 125 KB, respectively.

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Spatial Coverage

Thwaites Glacier, West Antarctica:

  • Northernmost Latitude: 75°S
  • Southernmost Latitude: 80°S
  • Westernmost Longitude: 120° W
  • Easternmost Longitude: 90° W

Spatial Resolution

Ice thickness data are spaced on a 15 km by 15 km ice thickness grid over the entire catchment of the glacier and sampled at approximately 15 m along track.

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Temporal Coverage

The AGASEA radar data from which this data set was derived were obtained between 7 December 2004 and 31 January 2005.

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Parameter or Variable

Table 2 below provides a description of each column in

Table 2. Column descriptions for
Column Description
1 Northing (polar stereographic -71 degrees)
2 Easting (polar stereographic -71 degrees)
3 Longitude (decimal degrees)
4 Latitude (decimal degrees)
5 Hydraulic Head (meters, WGS-84)
6 Surface Elevation (radar derived; meters, WGS-84)
7 Bed Elevation (radar derived; meters, WGS-84; 169 m/usec, no firn correction)
8 Flow Path Name (text)
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Sample Data

ASCII data are arranged in blocks, each representing a separate flow path. Blocks are separated by a line that begins with the ">" character followed by the flow path name, as illustrated by the following example from

sample data block

Figure 1 is a map showing the flow paths. The file contains a high-resolution version.

sample data map
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Software and Tools

Data can be read using standard spreadsheet software or with Global Mapping Tools, an open source collection of approximately 65 tools for manipulating geographic and Cartesian data sets.

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Data Acquisition and Processing

Data Acquisition Methods

Radar data were acquired by the Airborne Geophysical Survey of the Amundsen Embayment (AGASEA) expedition between 7 December 2004 and 31 January 2005, using the High Capability Radar Sounder Version 1 (HiCARS 1) VHF ice-penetrating radar system developed by the University of Texas Institute of Geophysics. HiCARS, which uses an 8 kW transmitter with a 1 μs FM chirp and a pulse repetition frequency of 6400 Hz, was operating with a 60MHz center frequency and 15 MHz of bandwidth. Across track beam width is controlled by the antenna beam pattern, and has a main cross-track half-power beam width of 12 degrees and side lobes at ±22 degrees.

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Derivation Techniques and Algorithms

Processing Steps

Radar data were down converted to a 10 MHz center frequency and recorded on two gain offset channels sampled at 50 MHz. Total dynamic range between the 2 channels is 90 dB. The data were coherently stacked 32 times to yield 16-bit, 3200-sample coherent records at 200 Hz, and during post-processing were range compressed with a synthetic chirp and filtered to remove 10 MHz coherent system noise.

Subglacial water flow paths were inferred by first using gridded ice thicknesses and bed elevations to generate a course map of hydrostatic potential, and then converting line-based ice thicknesses and bed elevations, derived from focused radar data, into lines of hydrostatic potential. Flow lines were constructed by selecting minima at obvious nickpoints and connecting them along fall lines of the grid.

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References and Related Publications

Contacts and Acknowledgments

Dr. Sasha P. Carter
Scripps Institution of Oceanography
University of California, San Diego
9500 Gilman Drive
La Jolla, CA 92093

Dr. Duncan A. Young
University of Texas at Austin
Institute for Geophysics
Mail Code R2200
10100 Burnet Road
Austin, TX 78758

Dr. Donald D. Blankenship
University of Texas at Austin
Institue for Geophysics
Mail Code R2200
10100 Burnet Road
Austin, TX 78758


This research was supported by the National Science Foundation (NSF) Office of Polar Programs (OPP) grant number 0636724.

Document Information


May, 2012

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