## 3 Data and Setup  
E6B data demodulation performance was assessed using real data collected by a high-end receiver mounted on board a Hurtigruten vessel. The vessel regularly sails along the Norwegian coast from Bergen to Kirkenes, and a full loop is completed in seven days. The sailing is performed at very high latitudes and most of the trip is within the Arctic Circle--the ship reaches latitudes higher than 71 degrees North. In addition, the vessel trajectory is surrounded by mountain peaks, steep cliffs, and fjords. The environmental conditions in which the data were collected make the observations unique and extremely valuable for assessing the E6B demodulation performance at high latitudes.  
To collect E6B data, a dedicated multi-constellation multi-frequency Septentrio PolarRx5S receiver was installed on the vessel. The receiver implements joint data (E6B) and pilot (E6C) tracking and was configured to collect data at one hertz. The antenna used for the data collection was a Trimble Zephyr Model 2 Geodetic GNSS and covers all Galileo frequency bands. A view on top of the vessel towards the Trimble antenna is provided in Figure 2.  
This setup allowed the collection of GNSS data at very high latitudes. A total of 50 GB of data were collected from January to March 2021 and used for analyses presented in this paper.  
Because the whole data collection was carried out at high latitudes, a reduction of about 15 degrees in the maximum satellite elevation was observed. To further showcase the latitude impact on the satellite geometry, the skylpot for users at different latitudes is shown in Figure 3 for a sample day and considering only Galileo satellites broadcasting E6 signals. The skylplots were obtained using almanac data from a reference station and considering users at different latitudes varying between 60 and 75 N degrees with a step of 5 degrees. Because the reference station collected data under ideal conditions, the satellite trajectories in the skylplots of Figure 3 correspond to ideal open sky conditions.  
The reduction of the satellite elevation when moving toward North is evident; in addition, the lack of satellites in the northern part of the skylpot is visible for users located at around 60 degrees latitude (e.g., Oslo). This gap is partially filled when further moving toward North. A similar trend can be observed for the entire period under observation.  
Figure 2: GNSS antenna mounted on board the Hurtigruten vessel sailing from Bergen to Kirkenes.  
The number of visible Galileo satellites is a crucial element in the estimation of the TTRD. For this reason, the number of visible satellites observed along the vessel trajectory is shown in the left part of Figure 4. The figure was produced by considering a full week of data collected on the vessel and considering observations with an epoch rate of five minutes. The number of satellites was determined considering an elevation mask of five degrees. For this reason, the number of visible satellites ranges from seven to twelve. Most of the satellites, however, have a low elevation and their number is significantly reduced when a mask of 15 degrees is applied. In this case, the number of satellites ranges from four to ten. In some part of the trajectory, a low number of satellites is recorded, and this is due to obstacles (fjord cliffs, mountains) blocking signal reception. The right side of Figure 4 shows the trajectory of the vessel color coded as a function of the Position Dilution Of Precision (PDOP) for the Galileo satellite constellation; the PDOP value varies according to the number of visible satellites and its median value is 1.83.  
Figure 4: Vessel trajectory color coded as a function of the number of satellites (**left**) and PDOP (**right**) based on Galileo satellite constellation.  
Figure 3: Skyplot for users at different latitudes. Different satellite passages are depicted with different colors.