Glacier stake locations, McMurdo Dry Valleys, Antarctica (1993-2020, ongoing)

Summary

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.

Date Range:

November 7, 1993 to January 29, 2020

Data Citation

Gooseff, M.N., Fountain, A.G. 2022. Glacier stake locations, McMurdo Dry Valleys, Antarctica (1993-2020, ongoing). Environmental Data Initiative. DOI: 10.6073/pasta/58c83eb53200c698cf6164a0b6ae92bf. Dataset accessed 18 April 2024.

Dataset(s)

Description:

Glacier stake locations

Variables (click to expand):

DATASET CODE

Label:
Definition: Code representing stake heights location dataset
Type: Nominal
Missing values: None specified

GLSTKID

Label: Glacier - Stake ID
Definition: Code formed with the Glacier, Stake and Date of measurement, used for legacy GIS mapping.
Type: Nominal
Missing values: None specified

GLACIER

Label: Glacier Name
Definition: Name of glacier where measurement was made
Type: Nominal
Missing values: None specified

STAKE

Label: Stake number
Definition: Unique number for each stake on glacier
Type: Nominal
Missing values: None specified

DATE_TIME

Label:
Definition: Date of data measurement.
Type: Date/time
Date format: MM/DD/YYYY
Missing values: None specified

LATITUDE

Label: Latitude
Definition: Sample Latitude
Type: Physical quantity
Unit: degree
Maximum: Not specified
Minimum: Not specified
Precision: Not specified
Missing values:
- Null = None given

LONGITUDE

Label: Longitude
Definition: Sample Longitude
Type: Physical quantity
Unit: degree
Maximum: Not specified
Minimum: Not specified
Precision: Not specified
Missing values:
- Null = None given

ELEVATION (m)

Label: Elevation
Definition: Elevation of sample site - from map.
Type: Physical quantity
Unit: meter
Maximum: Not specified
Minimum: Not specified
Precision: Not specified
Missing values:
- NULL = None given

COMMENTS

Label: Comments
Definition: Comments about the overall data or STAKE COORDINATES
Type: Nominal
Missing values: None specified

FILE_NAME

Label:
Definition: Name of file in which data was submitted
Type: Nominal
Missing values: None specified

File:

mcmlter-glac-stklocs-20220224.csv (39.97 KB)

Short name:

glstkloc

Dataset ID:

2000

People

Principal Investigator(s):

Michael N. Gooseff

Andrew G. Fountain

Contact:

McMurdo Dry Valleys LTER Information Manager

Associated Personnel:

Field Technician

Data Manager

Former Field Crew

Former Data Manager

Methodology

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.

Instrumentation:

NAVPRO 5000

GARMIN 45 GPS unit.

Trimble 4000 SSE receiver

Maintenance:

In 2015, Inigo San Gil moved these data to the Drupal Ecological Information Management System, thus modernizing a bit the way data is managed and distributed.

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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 and longitudes from degrees-minutes-seconds to degrees in decimal format. This would allow them to be stored in numeric format rather than as text.

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