GPS and GPR Data: Characteristics of Snow Megadunes and Their Potential Effect on Ice Core Interpretation

Summary

The Antarctic megadune research was conducted during two field seasons, one in November 2002 and the other in December 2003 through January 2004. The megadune field site is located on the East Antarctic Plateau, southeast of Vostok station. The objectives of this multi-facetted research are to determine the physical characteristics of the firn across the dunes including typical climate indicators such as stable isotopes and major chemical species and to install instruments to measure the time variation of near-surface wind and temperature with depth, to test and refine hypotheses for megadune formation. It is important to improve our current understanding of the megadunes because of their extreme nature, their broad extent, and their potential impact on the climate record. Megadunes are a manifestation of an extreme terrestrial climate and may provide insight on past terrestrial climate or on processes active on other planets.

Snow megadunes are undulating variations in accumulation and surface texture with wavelengths of 2 to 5 km and amplitudes up to 5 meters. The features cover 500,000 km² of the East Antarctic plateau, occurring in areas of moderate regional slope and low accumulation on the flanks of the ice sheet between 2500 and 3800 meters elevation. Landsat images and aerial photography indicate the dunes consist of alternating surfaces of glaze and rough sastrugi, with gradational boundaries. This pattern is oriented perpendicular to the mean wind direction, as modeled in katabatic wind studies. Glaze surfaces cover the leeward faces and troughs; rough sastrugi cover the windward faces and crests.  The megadune pattern is crossed by smooth to eroded wind-parallel longitudinal dunes. Wind-eroded longitudinal dunes form spectacular 1-meter-high sastrugi in nearby areas.

This data set contains ground penetrating radar (GPR) data showing surface morphology and internal layering structure along with global positioning system (GPS) data collected within an area of 60 km². GPS data are provided in space-delimited ASCII text Microsoft Excel formats, while GPR data are in JPEG format. Data are available via FTP.

Citing These Data

Scambos, T., and R. Bauer. 2006. GPS and GPR Data: characteristics of snow megadunes and their potential effect on ice core interpretation: GPS and GPR data. Boulder, Colorado USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N5Q23X5F.

Overview Table

Category	Description
Data format	Data are provided as space-delimited ASCII text files, Microsoft Excel (.xls) file, and JPEG image files.
Spatial coverage and resolution	Southernmost Latitude: 80.7802° S Northernmost Latitude: 80.5304° S Westernmost Longitude: 124.0218° E Easternmost Longitude: 126.0302° E
Temporal coverage and resolution	Data was collected on various dates during two field seasons; one in November 2002 and the other in December 2003 through January 2004.
Tools for accessing data	GPS data are viewable with a text editor or Microsoft Excel. GPR data can be viewed with image viewing software capable of opening JPEG files that are up to 16 MB in size.
File naming convention	See Directory Structure and File Naming Convention.
File size	File sizes range from 1 KB to 16 MB.
Parameters	Surface morphology and internal layering
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

Ted Scambos
National Snow and Ice Data Center
449 UCB, University of Colorado
Boulder, CO 80309-0449

Rob Bauer
National Snow and Ice Data Center
449 UCB, University of Colorado
Boulder, CO 80309-0449

Technical Contact

Acknowledgements

This research was supported by the National Science Foundation (NSF) Office of Polar Programs (OPP) grant OPP-0125276.

2. Detailed Data Description

Format

GPS data are available in Microsoft Excel format or in ASCII text format; GPR data are in JPEG format.

Directory Structure and File Naming Convention

GPR/

• mdunes_fdsfdn_250t_j10_rdr.jpg
• mdunes_n3mgd_250t_j09_20m_rdr.jpg
• mdunes_s1n1_100t_j07_rdr.jpg
• mdunes_s1n1_250t_sizes.jpg
• n3mgd.jpg
• s3mgdj08.jpg

GPS/

• GPS_data.xls - This file includes all of the data within this directory formatted as a spreadsheet workbook.
• mdunes_fdsfdn_250t_j10b_gps.txt
• mdunes_mgd-fds-fdn_gps_j10.txt
• mdunes_mgdn3_250t_j09b_gps.txt
• mdunes_mgd-n3_gps_j09.txt
• mdunes_mgd-s3-s1_gps_j08.txt
• mdunes_s1n1_100t_j07b_gps.txt
• mdunes_s3mgd_250t_j08b_gps.txt
• MGDpole_03jan04.txt
• MGDpole_04jan04.txt
• MGDpole_05dec02.txt
• MGDpole_08jan04.txt
• MGDpole_14jan04.txt
• MGDpole_17jan04.txt

File Size

File sizes range from 1 KB to 16 MB.

Spatial Coverage

Southernmost Latitude: 80.7802° S
Northernmost Latitude: 80.5304° S
Westernmost Longitude: 124.0218° E
Easternmost Longitude: 126.0302° E

Click on the thumbnail to view the regional GPR/GPS traverses (JPEG file, 120 KB).

Spatial Resolution

Investigators surveyed approximately 60 kilometers in distance during their traverses.

Temporal Coverage

GPS data were collected on 5 December 2002 and on various dates from 3 January 2004 through 17 January 2004.

GPR data were collected on 7 January 2004 through 10 January 2004. The profiles extend to approximately 50 m below the surface, a depth that corresponds to approximately 2,000 years before present.

Temporal Resolution

GPS data were recorded every 15 seconds during a traverse.

GPR samples were collected at 100 MHz and 250 MHz. For the resulting profiles, each dune layer represents approximately 400 years.

Parameter or Variable

Parameter Description

Dunes accrete into the wind and form stacked but tilted sequences that are approximately 10 m to 15 m thick with "glaze" areas that represent accumulation hiatuses of approximately 250 years.

Parameter Range

Dune structure is seen up to 60 m below the surface. This is confirmed by density profiles from ice cores.

Sample Image

Click on the thumbnail to view the radar profile (GIF file, 288 KB) collected on a traverse from the S1 pole to the N1 pole.

3. Data Access and Tools

Data Access

Data are available via FTP.

Volume

The entire data set is 37.7 MB.

Software and Tools

GPS data are viewable with a text editor or Microsoft Excel. GPR data can be viewed with image viewing software capable of opening JPEG files that are up to 16 MB in size.

See Also

• Antarctic Megadunes: Research at the Edge of the Earth
• AWS Data: Characteristics of Snow Megadunes and Their Potential Effect on Ice Core Interpretation

4. Data Acquisition and Processing

Sensor or Instrument Description

GPR:

• Used RAMAC System
• 100 MHz shielded
• 250 MHz shielded
• 32 stacks, ~700 - 1024 nsec
• 1 stacked trace/sec (1.35 sec)
• 60 km+ surveyed

GPS:

• Used Trimble 4400i, kinematic Base station at MGD Camp pole

Derivation Techniques and Algorithms

MATLAB code was used to process radar data and correct for surface elevation and density. Time of acquisition was converted to distance.

Processing Steps

GPR Post-processing:

• Removed local mean trace (200 traces running)
• Normalized by the mean absolute magnitude of mean the mean trace
• Smoothed by averaging traces (3-trace running mean)
• Corrected time-depth-density using density from main core
• Corrected for topography and converted time to distance using GPS profiles

5. References and Related Publications

Fahnestock, M. A., T. A. Scambos, C. A. Shuman, et. al. 2000. Snow megadune fields on the East Antarctic Plateau: extreme atmosphere-ice interaction. Geophysical Research Letters 27(22): 3719-3722.

6. Document Information

List of Acronyms

The following acronyms are used in this document:

ASCII: American Standard Code for Information Interchange
AWS: Automated Weather Station
FTP: File Transfer Protocol
GPR: Ground Penetrating Radar
GPS: Global Positioning System
JPEG: Joint Photographic Experts Group
NSIDC: National Snow and Ice Data Center
NSF: National Science Foundation
URL: Uniform Resource Locator
WGS84: World Geodetic Data System 1984

Document Creation Date

May 2006

Document URL

http://nsidc.org/data/docs/agdc/nsidc0282_scambos/index.html