GPS survey of 11 points for the David Glacier and its Drygalski Ice Tongue

Drygalski Ice Tongue is the largest ice tongue in Ross Sea. It is 70 kilometers
long (43.4 miles) and 20 kilometers wide (12.4 miles) and drains David Glacier.
This ice tongue is large enough to show up on maps of the Antarctic continent.
Drygalski Ice Tongue has been growing seaward 150 to 900 meters per year (492
to 2952 feet) for the past few decades.

Static GPS measurements were made starting from 1991 on the David Glacier and
on its Drygalski Ice Tongue. As reference station was adopted a 3D benchmark
installed on a rocky emergence at Hughes Bluff, while on the ice were fixed 8
alluminium pipes with distances to the reference station ranging from 3 to 120
km. During the survey the GPS antennas were fixed, by adapters for classical
tribach, directly on the top of the aluminum pipes permitting in this way a
solid and reliable autocentering positioning of the antennas. On the basis of
the reliable results obtained with this kind of benchmark the GPS measurements
were repeated in successive years, to investigate if seasonal or yearly
variations occur on the flow speed.

The same approach was used also to obtain information about Priestley and
Reeves Glaciers. Currently the numbers of points systematically measured are 11
for the David Glacier and its Drygalski Tongue, 3 for the Priestley Glacier and
Nansen Ice Sheet, 2 for the Reeves Glacier. In two successive days during the
1993/1994 expedition, 24-hour-long measurements using the GPS continuous
kinematic technique were performed on five points of the David Glacier and its
Drygalski Ice Tongue. At the same time two other GPS receivers were located,
the first on a fixed reference station , the second on the fast ice close to
Terra Nova Bay Station. The purpose of these measurements was to record the
response of floating Drygalski Ice Tongue to the ocean tide, in order to
individuate the position of the grounding line and the hydrostatic equilibrium
of floating area. Measurements of the same points have been repeated in
1992/1993, 1993/1994, 1994/1995 and 1995/1996.Data have been processed by
Geotracer v.2.25 software.