Glacier stake locations, McMurdo Dry Valleys, Antarctica (1993-2023, ongoing)

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.

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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.