The aim of these measurements is to locate points along profiles where the ice surface height difference between
high and low tides becomes significant. For that purpose, GPS measurements of the ice surface were performed
both at low and high tides over exactly the same points as displayed on the webmap.
The place where the difference in altitude becomes significant is then considered as a first approximation
of the grounding line along the correpsonding profile.
Carrier-phase differential GPS was used to determine the vertical altitude of the ice surface. A reference GPS receiver was set up on the nearest rock outcrop, while a rover unit was used to acquire positions according to the "Stop and Go" method over the successive points constituting the profiles. The corresponding baseline was short enough (15 km at the most) so as to ensure real time radio transmission of appropriate corrective terms (mostly ionospheric and atmospheric delays) from the reference to the rover and to allow for kinematic ambiguity resolution with "stop" recording phases not exceeding 30 seconds. Each of the measured points was precisely marked on the ground (using paint) in order for the second measurement to be performed at exactly the same place some 12 hours later. More information can be found in Le Meur et al., 2013.
In order to reproduce the altitudinal change along the profiles as displayed in figure 11 in Le Meur et al., 2013, you can use the diagram tool (top bar). You have to select the points you are interested in (preferably from a single profile) with the appropriate drawing tool (polygons are the best way of avoiding undesired points). The image below represents what can be obtained along the downflow profile, as the top panel of figure 11 in Le Meur et al., 2013.
Le Meur, E., M. Sacchettini, S. Garambois, E. Berthier, A. S. Drouet, G. Durand, D. Young, et al. « Two independent methods for mapping the grounding line of an outlet glacier – example from the Astrolabe Glacier, Terre Adélie, Antarctica ». The Cryosphere Discussions 7, no 4 (8th august 2013): 3969-4014. doi:10.5194/tcd-7-3969-2013.
16th to 19th january 2011, and 23th to 24th february 2011.