Get Data

Data Set ID:
NSIDC-0518

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.

Geographic Coverage

Spatial Coverage:
  • N: -75, S: -80, E: -90, W: -120

Spatial Resolution: Not Specified
Temporal Coverage:
  • 7 December 2004 to 31 January 2005
Temporal Resolution: Not specified
Parameter(s):
  • Glaciers/Ice Sheets > Glacier Elevation/Ice Sheet Elevation
  • Glaciers/Ice Sheets > Glacier Thickness/Ice Sheet Thickness
  • Glaciers/Ice Sheets > Glacier Topography/Ice Sheet Topography
Platform(s) AIRCRAFT
Sensor(s): RADAR
Data Format(s):
  • PDF
  • ASCII Text
Version: V1
Data Contributor(s): Sasha Carter, Duncan Young, Donald Blankenship

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.

Carter, S. P., D. A. Young, and D. D. Blankenship 2012. Subglacial water flow paths under Thwaites Glacier, West Antarctica, Version 1. [Indicate subset used]. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi: http://dx.doi.org/10.7265/N5RJ4GC8. [Date Accessed].

Back to Top

Collapse All / Open All

Detailed Data Description

Format

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

Background color on
File and Directory Structure

The FTP directory ftp://sidads.colorado.edu/pub/DATASETS/AGDC/nsidc0518_carter_V01 contains two files:

  • drains.xyz, an ASCII text file that contains the flow path data;
  • drains.xyz.pdf, a Portable Document Format file that contains a map of the flow paths.
Background color on
File Size

drains.xyz and drains.xyz.pdf are 48 KB and 125 KB, respectively.

Background color on
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.

Background color on
Temporal Coverage

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

Background color on
Parameter or Variable

Table 2 below provides a description of each column in drains.xyz.

Table 2. Column descriptions for drains.xyz
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)
Background color on
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 drains.xyz:

sample data block

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

sample data map
Background color on

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.

Background color on

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.

Background color on
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.

Background color on

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
USA

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

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

Acknowledgements: 

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

Document Information

DOCUMENT CREATION DATE

May, 2012

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

Access complete Knowledge Base

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