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This data set includes ice motion and topography measurements that were taken by measuring movement and altitude of poles set in the West Antarctic Ice Shelf. The data was acquired by Global Positioning System (GPS) measurements of poles. The position of the poles was measured twice; once in 2000, and again in 2002. Movement of the poles in that time show the ice motion velocity and direction.
GPS pole positions are given in latitude and longitude, and elevations are given in meters above the WGS1984 ellipsoid. The data are presented as tables in ASCII text files. Three maps of the area are included with the data tables.
The National Science Foundation (NSF) funded this work under grant number OPP-9909469.
Scambos, T., C. Raymond, H. Conway, and G. Catania. 2003. Ice Motion and Topography Near Margin Areas of Kamb Ice Stream. Boulder, CO: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N5WS8R52.
|Data format||Data are in ASCII text files and JPG image files.|
|Spatial coverage||the pole locations covered an area bounded by the following coordinates:
|Temporal coverage and resolution||Two measurements were taken for each location, the first between 11 November and 7 December 2000, the second between 11 January and 28 January 2002.|
|File naming convention||Ice Motion file names start with the line area covered and contain the word "motion"
Position file names contain the year, the line name, and either "GPS" or "pole"
Topography file names start with the line name, can include partial line designations, and the word "topo"
Map names contain line names
|File size||Text files range from 1 to 262 KB. Image files range from 248 to 462 KB.|
|Parameter(s)||GPS measurements were taken for position, elevation, and pole top elevation. Height from snow surface to the top of the poles was taken manually.|
|Procedures for obtaining data||Data are available via FTP.|
T. Scambos, National Snow and Ice Data Center; G. Catania, H. Conway, A.M. Gades, and C.F. Raymond, Earth and Space Sciences, University of Washington.
NSIDC User Services
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Thanks to Maurice Conway, for his work as Field Safety Officer and assistance in gathering GPS data.
Most of the GPS pole locations are shown in the images in the "maps" directory. The poles were set in 2000 and their positions were measured again in 2002. The "positions" directory contains the measurements taken in both years. The "topography" directory contains the data regarding the altitude of the poles. Based on the position data from 2000 and 2002, the location and elevation change data are located in the "icemotion" directory. The images in the "maps" directory also illustrate these changes.
Data are in ASCII text files. Image files in JPG format are provided as additional material.
Directory structure consists of four subdirectories:
The naming conventions for files are as follows:
|icemotion||Files are named for the a, b, c, and d lines shown in the scartrek_map.jpg map. All file names contain the word "motion." Example: cline.motion.txt|
|maps||There are three maps:
aandb.jpg - shows points along the A and B lines
bandc.jpg - shows points along the C and D lines
scartrek_map.jpg - shows a larger area encompassing all lines
|positions||File names consist of the measurement year (2000 or 2002), the location (line or area), the type of measurement (GPS or poles). Some files have two parts; for example: 2000aline1GPS.txt and 2000aline2GPS.txt.|
|topography||All files are named for the lines (a, b, c, etc.). Names include the "topo" to designate them as topographic file. Some file names also include the range of pole names (AE1552HtoAE15N2H) the file covers. There are also topography files that include the word "zigzag." These indicate the topography profile in and around the poles and give a regional representation of the topography.|
Text files range from 1 to 262 KB.to 262 KB. Image files range from 248 to 462 KB.
Data were collected along four traverses near Antarctica's Kamb Ice Stream (formerly known as Ice Stream C). See the images in the "maps" directory for precise traverse locations.
The map is taken from AVHRR EASE-Grid 25-KM 5:4 scale data
Two measurements were taken for each location, one in 2000 and one in 2002.
Most measurements were taken twice; once during the 2000 field season (between 11 November and 7 December) and again during the 2002 field season (between 11 January and 28 January).
GPS location poles were set and measured in 2000. These poles were left in place and measured again in 2002 to gather data on ice movement and to gather kinematic profiles of topography elevations between poles. GPS measurements were taken for position, elevation, and pole top elevation. Height from snow surface to the top of the poles was taken manually.
|Parameter||Unit of Measurement|
|Elevation||meters above WGS1984 ellipsoid|
|Distance from snow surface to top of pole||meters|
The following tables describe the columns of each type of table, and the parameter sensor, where applicable.
|pole||ID of the pole|
|lat||Latitude||Trimble SSE GPS receiver|
|long||Longitude||Trimble SSE GPS receiver|
|surfelev wgs1984||Surface elevation with respect to the WGS1984 ellipsoid||Trimble SSE GPS receiver|
|speed m/yr||Ice motion speed||Calculated from the difference in location between 2000 and 2002 measurements|
|bearing deg||Bearing degree||Calculated from the difference in location between 2000 and 2002 measurements|
|errsp m/yr||Error in speed (meters per year)||The net error of 2000 and 2002 measurements|
|errbr deg||Error in bearing degree||The net error of 2000 and 2002 measurements|
|vertvel m/yr||Apparent vertical displacement of the pole top (meters per year)||Calculated from the difference in location between 2000 and 2002 measurements|
|errvert m/yr||Estimated error of vertical motion (meters per year)||The net error of 2000 and 2002 measurements|
|pole||ID of the pole|
|lat 4-digit year||Latitude||Trimble SSE GPS receiver|
|long 4-digit year||Longitude||Trimble SSE GPS receiver|
|wgs1984 (pole top)||Elevation in meters of the pole top in relation to the WGS1984 ellipsoid||Trimble SSE GPS receiver|
|dxy||Error in meters in the latitude-longitude plane|
|dz||Error in meters for vertical measurement|
|pole ht (4-digit year)||Pole height in meters above snow surface||Manual measurement|
|file||GPS file name|
|epochs||Number of GPS epochs used to determine positions|
|lat (4-digit year)||Latitude||Trimble SSE GPS receiver|
|long (4-digit year)||Longitude||Trimble SSE GPS receiver|
|WGS1984 elevation||Surface elevation in meters with respect to the WGS1984 ellipsoid||Trimble SSE GPS receiver|
|distance||Distance in meters along the survey track from the central pole|
The following is a sample from the icemotion data file "abline1.motion.txt."
Typical GPS errors include ionosphere refraction, cycle skip, multipath errors. Errors associated with pole and antenna setup (wobble) are estimated to be less than 1 cm.
Accuracy of the measurements varied. Most pole measurements were accurate to within 1 - 8 cm in horizontal, and 2 - 20 cm vertical. A few measurements had lower accuracy (>0.5 meter error) due to interference from field radar measurement or ionospheric disturbance. In these cases, the vector in the JPG images is indicated in yellow. Topography surveys were generally accurate (repeatable) to ~15 cm vertical.
Data are available via Data are available via FTP.
Total volume of 37 text files is 1014 KB. Total volume of 3 image files is 1073 KB.
View the files using a Web browser or other compatible program. No special software is needed.
Investigators used the following naming convention for labelling the ice motion poles:
For topography-only surveys, the pole names consist of the line name and consecutive numbers. Some of these locations are not stationary, so the measurement was made from a snowmobile mount pole. These locations are labelled "RV" for rove.
GPS data were acquired using Trimble SSE GPS receivers. All data were collected with L1/L2 antennas with a ground plane. Surveys for most pole traverses and topography profiles were conducted in a stop-and-go kinematic style (Hulbe and Whillans, 1993) using two base stations. Some individual poles were measured using a fast static approach. Base station GPS data sets of (usually) 1 hour or more were processed using the AutoGIPSY service at the Jet Propulsion Laboratory (JPL). With precise coordinates from this service, GPSurvey was used to locate other poles and kinematic topography profiles.
GPS surveys were conducted in locations on the south side of Siple Dome and along Ridge B/C, which is now called the Englehardt Ice Ridge. An earlier field party set up the Siple Dome poles (see Antarctic Ice Velocity Data). These Siple dome poles were remeasured in 2000 and 2002.
In the Englehardt Ice Ridge, four regions (A, B, C, and D lines) were surveyed in 2000 and 2002 to determine ice motion at set poles and topography along pole traverses. Additional areas (BM, E, F, GL, L, M, and OH lines) were surveyed only once to determine precise topography.
Map of the entire study area. This image is a smaller version of "scartrek_map.jpg."
The three figures in the "maps" directory are derived from Moderate Resolution Imaging Spectroradiometer (MODIS) data. All images were acquired on 7 December 2000. The image "aandb.jpg" is a close-up view of the A and B lines in the Englehardt Ice Ridge and the Kamb Ice Stream area. This image shows ice motion pole grids and some pole IDs. Vectors in yellow had reported errors. Topography in this image comes from GPS only.
The image "candd.jpg" is a close-up view of the C and D lines of the Englehardt Ice Ridge and the Kamb Ice Stream area. This image shows ice motion pole grids and some pole IDs. Vectors in yellow had reported errors. Topography in this image comes from a combination of GPS and photoclinometry.
The image "scartrek_map.jpg" shows the entire study area. This images was processed to highlight the subtle ice topography. Red lines indicate GPS data locations. The solid red lines show lines or small grids of ice motion measurements (with topography traverses). Dashed red lines indicate topography-only surveys. (Blue dots and numbers show water accumulation measurements for another project. Yellow dots indicate sites of interest, including automated weather stations (AWS) and long-term ice motion sites acquired by Sridhar Anandakrishnan.) See Ice Velocity Data from Ice Stream C, West Antarctica for more information.
Anandakrishnan, S. 2001. Ice Velocity Data from Ice Stream C, West Antarctica. Boulder, CO: National Snow and Ice Data Center. Digital media.
Catania, G., H. Conway, A. Gades, C. Raymond and T. Scambos. 2001. GPR and RES reveal disturbed internal stratigraphy on Ridge B/C, Antarctica. 2001 WAIS Conference, Maryland.
Catania, G., H. Conway, A. Gades, C. Raymond, and H. Engelhardt. 2003. Bed-reflectivity beneath inactive ice streams in West Antarctica. Annals of Glaciology (37).
Conway, H., G. Catania, A. Gades, C. Raymond, and T. Scambos. 2001. Paleo-Ice Stream C0. 2001 WAIS Conference, Maryland.
Conway, H., G. Catania, C. Raymond, A. Gades, T. Scambos, and H. Engelhardt. 2002. Switch of flow direction in an Antarctic ice strean. Nature, (419), 465-467.
Hulbe, C., and Whillans, I. 1993. Stop-and-Go GPS in Anarctica. Surveying and Land Information Systems 53(2):151-158.
Scambos, T., H.Conway, C. Raymond, A. Gades, G. Catania, M. Fahnestock. 2001. The last thousand years of ice flow in the Siple Coast. 2001 WAIS Conference, Maryland.
All About GPS from Trimble Navigation, Ltd.
The following acronyms and abbreviations are used in this document.
|AWS||Automated Weather Stations|
|FTP||File Transfer Protocol|
|GPS||Global Positioning System|
|JPL||Jet Propulsion Laboratory|
|MODIS||Moderate Resolution Imaging Spectroradiometer|
|NSF||National Science Foundation|