GPS Ice Flow Measurements, Allan Hills, Antarctica
Summary
This data set includes includes high-precision GPS measurements of steel poles within the Allan Hills Main Ice Field, Near Western Ice Field, and extending to the eastern edge of the Middle Western Ice Field, in Antarctica. These data were collected between December 1997 and December 2010. The extended survey period allowed for vertical and horizontal velocities to be calculated with low associated error. Parameters include locations of poles in latitude and longitude, as well as elevation, ice velocity, and accumulation rates.
Data are available via FTP as ASCII text files in comma separated value (.csv) format. Raw data are also provided as Trimble raw data, compressed in .zip format, and supplementary information is provided in .csv format and portable document format (.pdf).
Citing These Data
Data Citation
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, dates of the data you used (for example, March to June 2004), publisher: NSIDC, and digital media.
Kurbatov, A, G. Hamilton, V. Spikes and N. Spaulding. 2011. GPS Ice Flow Measurements, Allan Hills, Antarctica. [list the dates of the data used]. Boulder, Colorado, USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N5NS0RSX.
Reference
The generation of this data set is discussed in the following article. We request that you acknowledge the use of this data set by referencing the following citation:
Spaulding, N. E., V. B. Spikes, G. S. Hamilton, P. A. Mayewski, N. W. Dunbar, R. P. Harvey, J. Schutt, and A. V. Kurbatov. 2012. Updates on Ice Motion and Mass Balance at the Allan Hills Icefield, Antarctica, with Implications for Paleoclimate Reconstructions. Journal of Glaciology. Vol. 58, No. 208, doi:10.3189/2012JoG11J176.
Overview Table
| Category | Description |
|---|---|
| Data format | ASCII text files in comma separated value (.csf) format Trimble raw data files compressed in .zip format Portable document format (.pdf) |
| Spatial coverage and resolution |
Southernmost Latitude: 76°50' S Northernmost Latitude: 75°40' S Westernmost Longitude: 159° E Easternmost Longitude: 159°15' E |
| Temporal coverage and resolution | 1997 to 2010 |
| File naming convention | TableS1.csv |
| File size | Files range in size from 4 to 12 KB. |
| Parameters | Latitude Longitude Elevation Time Ice flow vertical velocity Ice flow horizontal velocity Accumulation rates Point mass balance measurement Firn and ice density |
| Procedures for obtaining data | Data are available via FTP. |
Table of Contents
- Contacts and Acknowledgments
- Detailed Data Description
- Data Access and Tools
- Data Acquisition and Processing
- References and Related Publications
- Document Information
1. Contacts and Acknowledgments
Investigators
Dr. Andrei Kurbatov
Climate Change Institute
University of Maine
303 Bryand Global Science Building
Orono, Maine 04469
USA
Dr. Gordon Hamilton
Climate Change Institute
University of Maine
303 Bryand Global Science Building
Orono, Maine 04469
USA
Dr. Vandy Spikes
Earth Science Agency, LLC
PO Box 2858
Stateline, Nevada 89449
USA
Nicole Spaulding
Climate Change Insitute
University of Maine
303 Bryand Global Science Building
Orono, Maine 04469
USA
Technical Contact
NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org
Acknowledgements
This research was funded by the National Science Foundation (NSF) Office of Polar Programs (OPP) grant numbers 0838843, 0229245, and 9527571.
2. Detailed Data Description
Format
Data are provided as ASCII text files in comma separated value format. Raw data from the GPS sensors are provided as Trimble raw data files compressed in .zip format. Supplementary information is available in text format and PDF format.
File and Directory Structure
Data are available on the FTP site in the ftp://sidads.colorado.edu/pub/DATASETS/AGDC/nsidc0507_kurbatov_V01/ directory. Within this directory, there are four data files and four supplementary files. The directory also contains a folder (RawData) with the raw GPS data from all stations and years, in native Trimble format.
| Filename | Description |
|---|---|
| TableS1.csv | This data file provides the daily latitude, longitude, elevation, error and processing software used to calculate mean base station position each season. See Processing Steps for more information. |
| TableS2.csv | This data file shows the position of each pole, along with horizontal and vertical velocity and direction, and estimates of accumulation rates via the change in the height of the pole above the snow surface. |
| TableS3.csv | This file provides the error associated with each reported position. See Error Sources for more information. |
| TableS4.csv | This file provides ice motion and surface balance data. |
| Filename | Description |
|---|---|
| DecimalYearsCalc.csv | Shows the days during which surveys were conducted and the calculated median day. Calculated median day is used to determine the decimal year value used in the calculation of velocities, accumulation rates and mass balance. |
| Equipment.csv | Shows the receiver and antenna types, as well as the processing software used each season. |
| DensitySupplement.pdf | Appendix D from Spikes, V.B., 2000. Laser altimetry, mass balance, and meteorites: A two part study of ice streams and blue ice, (Master's thesis), Ohio State University. Shows location and range of density measurements, used to determine density values for mass balance calculation. |
| Files.txt | Contains a description of each of the files in the data set |
File Naming Convention
Data and supplementary files are named as described above. Raw data are provided as .zip files, and are named according to the following convention.
xxxxDDDN.bin
Where:
| Folder Name | Description |
|---|---|
| xxxx | Equipment used: Codes for data change yearly. See Table 4. |
| DDD | Julian day of data collection |
| N | File number for day: 0 refers to the first file of a day. |
| .bin | File extension: .dat is for processing, .o and .n are the RINEX files, all others for satellite position corrections. |
| Year | Information |
|---|---|
| 1997 and 1999 | Only base files are included. In these year the first four characters (referring to the equipment) were changed to reflect that they were base stations, thus base and aln0 have no real meaning. |
| 2004 | As in 1997 and 1999 the first four characters of the file have been changed. BASE indicates that it is a base station file. In this year two separate rover units are used, the first four characters of their files are ROLL and ROYC. Each rover file has multiple positions: when processed the name of each pole for each position will be visible. |
| 2010 | t01 is a base file, t00 is a rover file. Both must be converted to .dat to use in GPS processing software. They can also be converted directly to Receiver Independent Exchange (RINEX) files (.obs, .nav and in earlier years .o and .n) for use in precise positioning. The file naming convention stays the same so for the base the first four digits (1948) refers to equipment type, same for the rover (1503). Each rover file has a single position, and the readme file provides the name of each station (pole) the position is ascribed to. |
File Size
Data files range in size from 4 KB to 12 KB.
Spatial Coverage
Data were collected in the Allan Hills region of Antarctica, at the Allan Hills Main Ice Field, Near Western Ice Field, and extending to the eastern edge of the Middle Western Ice Field.
Southernmost Latitude: 76°50' S
Northernmost Latitude: 75°40' S
Westernmost Longitude: 159° E
Easternmost Longitude: 159°15' E
Projection
All positions are provided in WGS 1984 South Polar Stereographic Projection with a standard parallel of -71S, 0E and a false Easting and Northing of 0.
Temporal Coverage
1997, 1999, 2004, and 2010
Parameter or Variable
Parameter Description
| Parameter | Description |
|---|---|
| Station | Name of GPS station (pole) |
| Year/Day | Year and Julian day of data collection |
| Longitude(dddmmss.ss) | GPS longitude position in degrees minutes seconds |
| Latitude(ddmmss.ss) | GPS latitude position in degrees minutes seconds |
| Elevation (m) | Ice sheet elevation in meters |
| SigX | Error in longitude |
| SigY | Error in latitude |
| SigZ | Error in elevation |
| Software | Software used to determine precise position |
| StdDevElev | Combined error for average elevation |
| Parameter | Description |
|---|---|
| Pole |
Name of GPS station (pole) |
| X(km) Y(km) Z(m) | Coordinate in WGS 1984 South Polar Stereographic projection with a standard parallel of -71°S, 0°E, and a false Easting and Northing of 0 |
| PoleHeight(m) | Height of pole from ice surface to antennae phase center (meters) |
| hor.vel.(m/a) | Horizontal ice velocity in meters per year |
| azimuth(rad) | Direction of ice motion in radians |
| azimuth(deg) | Direction of ice motion in degrees |
| ver.vel(m/a) | Vertical ice velocity in meters per year |
| dPoleHeight(m) | Change in pole height between years |
| dPoleHeight(m/a) | Change in pole height per year |
| Parameter | Description |
|---|---|
| Station |
Name of GPS station (pole) |
| 3D-RMS(m) | Combined root mean square error for pole position (east/west, north/south, and up/down) |
| dNorth(m) | Change in north/south pole position |
| dEast(m) | Change in east/west pole position |
| dHorizontal(m) | Change in ice elevation |
| dUp(m) | Change in combined north/south and east/west position |
| std.dev. (hor) | Standard deviation of change in ice elevation |
| std.dev. (up) | Standard deviation in change in combined north/south and east/west position |
| Parameter | Description |
|---|---|
| pole name | Name of GPS station (pole) |
| X | Easting coordinate in WGS 1984 South Polar Stereographic with a standard parallel of -71S, 0E and a false Easting and Northing of 0 |
| Y | Northing coordinate in WGS 1984 South Polar Stereographic with a standard parallel of -71S, 0E and a false Easting and Northing of 0 |
| Z | Ice sheet elevation |
| vel | Horizontal ice velocity |
| dZ | Change in pole height |
| bdot | Accumulation rate |
| bdot | Surface density adjusted accumulation rate |
| surf_den | Surface snow/firn density |
| 1m_den | Snow/firn density at 1 meter |
| bdot/den | Final adjusted accumulation rate |
| slope | Slope of ice surface at station |
| azimuth | Direction of ice motion |
| slope*vel | Slope multiplied by ice velocity |
| Hdot | Rate of thickness change of the ice surface |
| uncertainties | Error calculated in each of the above |
Sample Data Record
| Station | Year/Day | Longitude(dddmmss.ss) | Latitude(ddmmss.ss) | Elevation (m) | SigX | SigY | SigZ | Software | StdDevElev |
| ALN0 | 1997/338 | 159o31_42.543__ | 76o42_38.969__ | 1961.31 | 0.0014 | 0.0017 | 0.0041 | APPS | |
| ALN0 | 1997/340 | 159o31_42.543__ | 76o42_38.969__ | 1961.31 | 0.0016 | 0.0019 | 0.0047 | APPS | |
| ALN0 | 1997/Avg. | 159o31_42.543__ | 76o42_38.969__ | 1961.31 | 0.0015 | 0.0018 | 0.0044 | APPS | 0 |
This sample data record shows the first four rows in the TablesS1.csv file.
Error Sources
Error information is provided in the TableS4.csv file. 3D-RMS includes dNorth, dEast and dUp. dHorizontal is the 2D-RMS and therefore includes dNorth and dEast. Std.dev.(hor) and std.dev.(up) is the total error associated each pole position.
3. Data Access and Tools
Data Access
Data are available via FTP.
Volume
Total volume of the data set is 89 MB.
Software and Tools
Data files are accessible using spreadsheet software. Raw data files require Trimble Business Center software.
4. Data Acquisition and Processing
Theory of Measurements
Surface balance and ice motion were derived from high-precision GPS measurements at a network of steel poles at three areas in the Allan Hills Blue Ice Area. Detailed description of the measurement methods is provided in Spaulding et. al. 2012.
Sensor or Instrument Description
Data were collected using GPS sensors of various types. These are described in the Equipment.csv file.
Processing Steps
All base station data were processed using JPL's Automatic Precise Positioning Service (APPS) system in 2011 to ensure the same International Terrestrial Reference Frame (ITRF) 2005 version was used. The 1997 and 1999 data were previously processed using Generalized Information Processing System (GIPSY) and the 1995 ITRF, so the vertical positions had a bias when compared to the 2004 and 2010 data. As a result the 1997 and 1999 data have been shifted vertically down 0.141 m to account for the bias introduced by different ITRF versions. This shift was also applied to each survey pole, as they had previously been shifted to account for this bias in 1999. In 2010 only the base station data from days when pole surveys were conducted is used, resulting in a height that is 0.022 m higher than previously determined, so all 2010 pole data were shifted up 0.022 m.
5. References and Related Publications
Spaulding, N. E., V. B. Spikes, G. S. Hamilton, P. A. Mayewski, N. W. Dunbar, R. P. Harvey, J. Schutt, and A. V. Kurbatov. 2012. Updates on Ice Motion and Mass Balance at the Allan Hills Icefield, Antarctica, with Implications for Paleoclimate Reconstructions. Journal of Glaciology. Vol. 58, No. 208, doi:10.3189/2012JoG11J176.
Spikes, V. B. 2000. Laser Altimetry, Mass Balance, and Meteorites: A Two Part Study of Ice Streams and Blue Ice. Master's thesis: Ohio State University.
6. Document Information
Acronyms
The following acronyms are used in this document.
| Acronym | Description |
|---|---|
| AGDC | Antarctic Glaciological Data Center |
| APPS | Automatic Precise Positioning Service |
| ITRF | International Terrestrial Reference Frame |
| GIPSY | Generalized Information Processing System |
| GPS | Global Positioning System |
| JPL | Jet Propulsion Laboratory |
| NSIDC | National Snow and Ice Data Center |
| RINEX | Receiver Independent Exchange |
| URL | Uniform Resource Locator |
Document Creation Date
13 December 2011
Document URL
http://nsidc.org/data/docs/agdc/nsidc0507_kurbatov/index.html
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