# GNSS Profile from the Greenland Korth Expeditions in the Context of Satellite Data
## 2 Greenland Korth Expeditions  
In 2002 the project \"Spurensuche\" (in English: search for tracks), hereinafter called the Greenland Korth Expeditions (Greenland Korth Expeditions), was started. A four-person German expedition team under the direction of [PERSON] crossed the Greenland ice sheet from Isotora on the east coast to Port Victor (historically Quervains Havn) at Disko Bay on the west coast. The historical model for this expedition was the 1912 Swiss Greenland expedition under the direction of [PERSON]. After [PERSON] in 1888, this expedition was the second successful crossing of the Greenland ice sheet. They took a 700 km long traverse. Since the beginning, the Swiss expedition was meant to be a scientific exploration of the Greenland ice sheet. The group of four researchers carried out numerous geodetic and meteorological measurements. [PERSON] (meteorologist and expedition leader), [PERSON] (doctor), [PERSON] (engineer) and [PERSON] (architect, responsible for geodetic measurements) were members of the expedition that crossed the ice sheet using dog-sledges (Figure 1). As a result of this expedition, the first elevation profile of the ice sheet was published [10]. Ninety years later, this historic route was taken again and measured with modern GNSS technology. The scientific director was [PERSON] from the Technical College of Higher Education in Berlin (today: Beuth University of Applied Sciences Berlin). Since the Greenland ice sheet is an important sensor for climate change, the results of repeated measurements over longer periods (e.g., height comparisons) can provide insight into this process. For this reason, in 2006 a group of six people crossed the ice sheet again [11]. As in 2002, the direction of the expedition was given to [PERSON] and the scientific direction to [PERSON]. Every four years, a group led by [PERSON] followed the footsteps of [PERSON] [12]. In 2010 a three-person group crossed the ice sheet and in 2012 a four-person anniversary expedition was planned, which had to be cancelled after about 100 km due to material damage [13]. For the expeditions described above, a similar measuring program was implemented [11]. The GNSS measurements were carried out with a Trimble Zephyr Geodetic antenna and the Trimble 5700, and later the Trimble R7, served as the receiver. Static GNSS measurements were carried out with observation times of several hours overnight at the campsites. In total, 35 measurements were made, together comprising the elevation profile presented here. Therefore, the following expeditions were tied to the places given in 2002. The expedition members had to reach them and use them as a campsite, even if the conditions were significantly worse or better. This procedure allowed made it possible to make an estimate about the shrinking or growing of the ice sheet at specific positions based on the differences in elevation. Certain tendencies can already be read from the repeated measurements, e.g., an increase in the melting process in the coastal areas. In addition to the static measurements overnight, kinematic GNSS measurements were carried out at the camps. This was done in a radius of more than 100 m around the camp. The scatter plot of coordinates was then interpolated to a fitted plane. This  
Figure 1: Participants of the historic Swiss Greenland expedition in 1912 (from left: [PERSON], [PERSON], [PERSON], [PERSON]). simple adjustment with a standard deviation of a few centimeters is possible on snow and ice surfaces. Roughness does not disrupt the results [14]. With the help of the grid and the interpolated plane, the points of the static measurement can be verified and the comparison with earlier measurements is possible with higher quality. This works also when the subsequent measurement does not take place at exactly the same point. If the amount of ice movement is known in addition, by means of this approach a specific mass balance can be estimated [14]. The inclination of the surface can be determined from the middle plane.