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Data Set ID:
NSIDC-0507

GPS Ice Flow Measurements, Allan Hills, Antarctica, Version 1

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).

Geographic Coverage

Parameter(s):
  • Glaciers/Ice Sheets > Glacier Mass Balance/Ice Sheet Mass Balance
  • Glaciers/Ice Sheets > Glacier Motion/Ice Sheet Motion
  • Glaciers/Ice Sheets
  • Glaciers/Ice Sheets > Glacier Topography/Ice Sheet Topography
  • Snow/Ice > Ice Motion
  • Snow/Ice > Ice Velocity
  • Snow/Ice
Spatial Coverage:
  • N: -76.66667, S: -76.83333, E: 159, W: 158.25

Spatial Resolution: Not Specified
Temporal Coverage:
  • 4 December 1997 to 19 December 2010
Temporal Resolution: Not specified
Data Format(s):
  • PDF
  • ASCII Text
Platform(s) FIELD INVESTIGATION, FIELD SURVEYS
Sensor(s): GPS
Version: V1
Data Contributor(s): Andrei Kurbatov, Vandy Spikes, Gordon Hamilton, Nicole Spaulding
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.

Kurbatov, A. V., G. S. Hamilton, V. B. Spikes, and N. Spaulding. 2011. GPS Ice Flow Measurements, Allan Hills, Antarctica, Version 1. [Indicate subset used]. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi: http://dx.doi.org/10.7265/N5NS0RSX. [Date Accessed].

Literature Citation

As a condition of using these data, we request that you acknowledge the author(s) of this data set by referencing the following peer-reviewed publication.

  • Spaulding, N. et al. 2012. Ice Motion and Mass Balance at the Allan Hills blue-ice area, Antarctica, with Implications for Paleoclimate Reconstructions, Journal of Glaciology. 58. 399-406. http://dx.doi.org/10.3189/2012JoG11J176

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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.

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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.

Table 1. Data File Description
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.
Table 2. Supplemental File Description
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
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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:

Table 3. File Naming Convention for Raw Data Files
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.
Table 4. Naming Convention for First Four Digits of Raw Data Files
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 baseand 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.
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File Size

Data files range in size from 4 KB to 12 KB.

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Volume

Total volume of the data set is 89 MB.

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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 Description

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.

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Temporal Coverage

1997, 1999, 2004, and 2010

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Parameter or Variable

Parameter Description

Table 5. Parameter Description for the TableS1.csv File
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
Table 6. Parameter Description for the TableS2.csv File
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
Table 7. Parameter Description for the TableS3.csv File
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
Table 8. Parameter Description for the TableS4.csv File
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.

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Software and Tools

Data files are accessible using spreadsheet software. Raw data files require Trimble Business Center software.

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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.

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Derivation Techniques and Algorithms

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.

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.

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Sensor or Instrument Description

Data were collected using GPS sensors of various types. These are described in the Equipment.csv file.

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References and Related Publications

Contacts and Acknowledgments

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

Acknowledgments: 

This research was funded by the National Science Foundation (NSF) Office of Polar Programs (OPP) grant numbers 0838843, 0229245, and 9527571.

Document Information

Document Creation Date

13 December 2011

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