bjtn@pdx.edu
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.
GPS Measurements Made on Taylor Valley Glaciers With Help From UNAVCO.
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.
 |
 |
 |
| A. Canada Glacier |
B. Canada Glacier |
C. 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:
| 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 |
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.
| VARIABLE |
TYPE |
DESCRIPTION |
UNITS |
MISSING VALUE INDICATOR |
MINIMUM |
MAXIMUM |
PRECISION |
| 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 |
Gayle Dana making a measurement on the horizontal stake
with a vertical stake visible. The glacier is Canada Glacier.
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
(jenh@snobear.colorado.edu; (303)492-4639) so that the data can be
corrected or qualified. Thus, these data may be modified and future
data will be appended.
