GLACIER STAKE LOCATIONS

Stake Locations All Rights Reserved. Reproduced with permission.

• The Principal Investigator be sent a notice stating reasons for acquiring any data and a description of the publication intentions.
• The Principal Investigator be sent a copy of the report or manuscript prior to submission and be adequately cited in any resultant publications.
• A copy of any resultant publications should be sent to the McMurdo data manager.
  

MCM LTER Data Manager:	Chi Yang
Address:	Institute of Arctic and Alpine Research, Campus Box 450, University of Colorado Boulder, Colorado 80309-0450
Phone:	(303) 492-4639
E-Mail:	Chi.Yang@colorado.edu

PRINCIPAL INVESTIGATOR:	Andrew G. Fountain
Address:	Department of Geology, Portland State University, Portland OR, 97207-0751
Phone:	(503)725-3022
E-Mail:	fountaina@pdx.edu

OTHERS:	Thomas Nylen
Address:	Department of Geology, Portland State University, Portland OR, 97207-0751
Phone:	(503)725-3355
E-Mail:	nylent@pdx.edu

• To retrieve glacier stake locations, click here (Comma Delimited Ascii Format).
  

• Descriptions of previous adjustments to the data files can be found in the log section of this page.

KEYWORDS: glacier, GPS, global positioning system, latitude, longitude, elevation, Antarctica, LTER

ABSTRACT: As part of the Long Term Ecological Research (LTER) project in the McMurdo Dry Valleys of Antarctica, a systematic sampling program has been undertaken to monitor mass balance and meltwater flow from the Taylor Valley glaciers. This data set contains global positioning system (GPS) measurements of stakes on glaciers. The measurements include both low-quality estimates (+/- 100m) from hand-held GPS units and high precision measurements (+/- 2 cm) using Trimble (4000 SSE) geodetic receivers. The purpose of these measurements was to obtain rough stake locations for use in relocating stakes in the future and precise stake locations for use in calculating stake displacement. The measurements are made relative to the WGS84 ellipsoid.

VARIABLES: dataset code, glstkid, glacier, stake, date, latitude, longitude, elevation (m), comments, file name

RESEARCH LOCATION: Data was collected from the Canada, Commonwealth, Howard, Hughes, Suess and Taylor glaciers, located in the Taylor Valley, McMurdo Dry Valleys, Antarctica. This data file specifies the latitude, longitude, and elevation of the stakes used on those glaciers.

METHODS: Handheld measurements were acquired using either a NAVPRO 5000 or GARMIN 45 GPS unit. Latitude and longitude accuracy are about +/- 100m. The handheld units did not provide adequately accurate elevations, so elevation was acquired from the 1971 map of the valley. There was no special procedure in acquiring the data or exact location relative to the stake.

The precise GPS measurements were acquired with help of UNAVCO. (See photos and further descriptions below). Measurements were made using a Trimble 4000 SSE receiver. A base station was set up prior to measurements in the field. The baseline between the measurements and basestation did not exceed 15 km. The measurements were collected as rapid static surveys.

For the precise measurements, the GPS antenna was mounted on top of a 2 meter tall rangepole. The rangepole was placed next to the each ablation stake on the down-glacier side of the stake, and the tip of the rangepole was placed on the board used for mass balance measurements at that stake to insure that the measured elevation was relative to the same surface used in the mass balance measurements. This system resulted in the rangepole sitting 2-3 cm away from the down-glacier side of the ablation stake. Repeatibility of placement was ascertained to be about +/- 2 cm based on repeat measurements. The rangepole was always vertical, as indicated by a level-bubble.

At each stake, data were collected for 10 - 20 minutes, sufficient to keep the horizontal precision of the GPS results within 2 cm. Accuracy of the resulting measurements are estimated to be 5 cm in the horizontal and vertical, after accounting for set-up error.

During the 1995/96 season, the position of all the ablation stakes on four different glaciers were measured using rapid-static GPS. A re-measurement in the 1996/97 season provided displacements and velocities. These photos show the following:

A. Karl Feaux of UNAVCO and science researcher Paul Langevin conducting a rapid static survey on the Canada Glacier, Taylor Valley.	B. Bjorn Johns of UNAVCO conducting a rapid static survey of the Canada Glacier.	C. ASA mountaineer Steve Dunbar and science researcher Paul Langevin conducting snow accumulation measurements and a GPS rapid static survey on the Howard Glacier, Taylor Valley.
Canada Glacier	Canada Glacier	Howard Glacier
For a more detailed description of how global positioning system measurements were used for the McMurdo Dry Valley research, click here.

TIMING: Handheld GPS measurements were initiated in November of 1993 and have been updated since that time (precise measurements supercede handheld). Precise measurements are intermittently repeated when opportunity permits, to measure rate of stake displacement.

CITATIONS:

COMMENTS:

STATUS: Public Access (Type 1).

VARIABLE DESCRIPTION: Listed below are the descriptions of the three data files:

VARIABLE	TYPE	DESCRIPTION	UNITS	MISSING VALUE INDICATOR	MINIMUM	MAXIMUM	PRECISION
Dataset code	Text	Code representing glacier stake locations dataset	None	Required entry	n/a	n/a	n/a
Glstkid	Text	Code from glacier / stake / date of coordinate measurement (to be used for GIS mapping)	None	Required entry	n/a	n/a	n/a
Glacier	Text	Name of glacier where measurement is made	None	Required entry	n/a	n/a	n/a
Stake	Text	Unique number for each stake on glacier	None	Required entry	n/a	n/a	n/a
Date	Date	Date measurement was made	mm/dd/yyyy (month / day / year)	Required entry	11/01/1993	12/31/2004	n/a
Latitude	Number	Angular distance south of equator	degrees	Null	-90	0	0.000001
Longitude	Number	Angular distance east of Greenwich meridian	degrees	Null	0	360	0.000001
Elevation (m)	Number	Height of stake location above sea level	meters	Null	0	10	0.1
Comments	Text	Comments regarding stake coordinates	None	Null	n/a	n/a	n/a
File Name	Text	Raw data file containing information	None	Null	n/a	n/a	n/a

Note: A stake with an H or V indicates a stake along the ice cliff that forms the boundary of the glacier terminus. An H is a horizontal stake placed into the vertical wall of the glacier terminus, and V is a stake placed into the ice apron at the base of the ice cliff (see photo below). The vertical stakes were installed to support the horizontal stakes and provide a nearby measure of ablation for a surface with a much different slope.

LOG:Data for the original stake locations was submitted by Andrew G. Fountain to the data manager in August, 1997. The column showing "file name" identifies the original file containing that record. These are ascii text files and can be found in the McMurdo LTER data manager's home directory on INSTAAR's Unix system.

Once submitted to INSTAAR, the data manager used Microsoft Excel and Access software to produce files that were in more of a relational mode. The resulting files are represented in the "glstkloc.dat" file (ascii text, comma delimited format), and "glstkloc.txt" file (MS-DOS text format).

Initially, there was no date associated with each record in the data file. However, due to constant movement of ice on glaciers, the stake locations required subsequent measurements during the 1996-97 field season. When this occurred, a field for date was added to this file. Dates from the initial GPS measurements were acquired from the raw data files submitted by Andrew Fountain. If uncertain about what date to use, confirmation was made with Karen Lewis.

Upon verifying altitude corrections for the gps locations with Bjorn Johns of UNAVCO (in March, 1998), Karen Lewis discovered that all of the ellipsoidal heights to sea level obtained by precise GPS measurements were too short by 55.24 meters. Denise Steigerwald therefore adjusted the elevations for these stakes by adding 55.24 meters.

In April, 2000, Denise Steigerwald added fields for dataset code and glstkid. Dataset code would allow the data to be linked to the metadata in a relational database. Glstkid is a code that ties stake records to points on a GIS base map being developed by Michael Prentice at the University of New Hampshire. In addition, Denise:

• Removed records associated with "B" (replacement) stakes. Coordinates for these stakes match those provided for the original stakes. Data sets containing replacement stake records had their stake values divided into 'stake' and 'stk replcmnt' fields, thus allowing the 'stake' fields to be linked between the locations file and the data files.
• Converted all latitudes & longitudes from degrees-minutes-seconds to degrees in decimal format. This would allow them to be stored in numeric format rather than as text.

NOTE: Data contained in these files has been subjected to quality control standards imposed by the investigator. The user of this data should be aware that, while efforts have been taken to ensure that these data are of the highest quality, there is no guarantee of perfection for the data contained herein and the possibility of errors exists. If you encounter questionable data, please contact the MCM LTER data manager (telephone: 303-492-4639) so that the data can be corrected or qualified. Thus, these data may be modified and future data will be appended.