# GNSS Profile from the Greenland Korth Expeditions in the Context of Satellite Data
## 2 Greenland Korth Expeditions
The repeated measurement in 2006 showed no changes in inclination, which suggests a locally uniform melting or growth [15]. Reference data from the International GNSS Service were used to correct the data [11; 16]. An exception is the expedition in 2006, during which a reference station on the coast of Greenland was monitored by two students. The evaluation was carried out by different people with different software. _Trimble Total Control_, _Trimble Business Center_ and _Bernese GNSS Software_ from the Astronomical Institute of the University of Bern were used. Handheld GNSS devices were also used during each expedition since 2006. In addition to the geodetic measurements, meteorological data (temperature, atmospheric pressure, wind velocity, etc.) were recorded during the expeditions. Permanent magnets with a diameter of 45 mm, a thickness of 9 mm and a known magnetic moment were used as marks [11]. After a return to the same location during the following expedition, these magnets reached a new position and depth due to the ice movements and accumulation. An area the size of a football/soccer field (100 m \(\times\) 70 m) was scanned with a magnetometer at a grid spacing of 3 m in order to determine magnetic anomalies caused by the movement of the magnets. According to theoretical considerations, depth can be estimated from the maximum value of the magnetometer measurement at the surface (for more details, see [11]). The signal gets weaker with increasing depth, and in the present case the limiting depth is about 5 m below the surface. In 2006 one particular magnet was dug up to check the real position and depth against the estimates of these two coordinates based on surface magnetometer measurements. Both the position (a position error of less than 30 cm) and the depth (magnetometer estimate: 4.1 m; actual depth: 4.12 m) were extremely precise. With this method, exact ice movements and the annual accumulation can be determined [11]. A differentiation can be made between the accumulation area (increase; snow remains) and ablation area (loss of mass). In between, there is the equilibrium line or equilibrium zone. Another successful crossing of the ice sheet took place in 2015 by a group of four under the direction of [PERSON] [17]. For the first time, the route was examined with kinematic GNSS measurements in order to generate an almost continuous profile. With this method it is possible to compare the entire profile and not only the positions of the campsites. The Trimble R7 receiver and the NavXperience 3G+C antenna were used on the expedition. The antenna was screwed onto a frame that was braced on the pulka (Figure 2a). Since this system was being tested for the first time, the static measurements continued overnight. A great advantage of the kinematic method was that the camps and measurement points set up in 2002 did not necessarily have to be reached and the length of the daily stages could be made dependent on the conditions. Nevertheless, a relatively large number of previous camps were reached enabling repeated measurements, so that the static measurements also remained significant. In addition, meteorological data were recorded several times a day and scanning retro-reflectors were measured by InSAR and Remotely Piloted Aircraft Systems (RPAS) on the west coast. Two of the reflectors are located on the mainland and the other two are on the ice sheet (data courtesy of Prof. [PERSON], Czech Technical University, Prague). After the expedition, satellite images of the area were evaluated in order to determine the speed and direction [18; 19]. In 2017 a smaller expedition took place on the east coast of Greenland [12; 20]. The group of three followed the crossing route almost until the Arctic Circle and returned to the coast along the old route of de Quervain. Nearly continuous kinematic GNSS measurements took place. Static measurements were carried out at some campsites and cross sections were recorded with the GeoExplorer 6000. Meteorological and glaciological data were also collected.