Appl. Sci. 2023, 13, 1872 
90{17 
Table 1. Distance between the transmitters and the centre point of the test area. 
Station Name Lat [deg] Lon [deg] Distance [km] 
Hoburg 56.9209 18.1520 
Rozewie 54.8308 18.3347 
Holmsjö 56.4440 15.6551 
Helgoland 54.1859 7.9052 
Hammerodde 55.2981 14.7738 
Groß Mohrdorf 53.3740 12.9344 
58 _00°N 
‘est Area 
MF Station 
An Julg 
„1510 
" 
U 
DD, 56.00°N 
Als 
ww 
5 
meraodde 
5 
[4] 
5 
„VOZEWIE 
Jroß !Johrdorf 
leere 
54 .00°N 
Q0°EH 
15 00° 
:$ 00°B 
18 .00°E 
Longitude [deg] 
Figure 6. MF transmitters (yellow triangles) available during the campaign and test area (red rectangle). 
The DLR receiver was operating with a sampling frequency of 1 MHz, and the observa- 
tion time for the Fast Fourier Transform (FFT) algorithm, which provides phase estimates, 
was set to 1s. Measurements with 1 Hz frequency resolution were therefore obtained. A 
GPS-stabilized rubidium clock, which ensured the synchronization with GPS time, was 
used in the setup. This is in general not required, but it is relevant in a research and 
development phase to assure stable measurements, helping in the identification of further 
problems or issues. Additionally, the setup included a Saab R5 GNSS receiver operating 
in a real-time kinematic (RTK) mode by using the Hemisphere Atlas Global Correction 
Service, which assured a very accurate reference track, with an accuray of 8 cm (95%) [28], 
and was used to determine the R-Mode horizontal positioning error. 
4.1. Daytime Results 
The results presented in this section are related to data recorded during the day. 
Moreover, the impact of the AGDF for this data set was almost negligible, due to the 
limited area in which the vessel was operating. We therefore rate the scenario as “optimal” 
ın the sense that the achievable accuracy depends mainly on the receiver noise and the 
signals’ received power. The data set was recorded between 7:56 UTC and 14:00 UTC, and 
at least one signal per radio beacon was usable during this time. This means that all the 
transmitters were used in the positioning solution. The signals used are visible in Table 2 
with the “h” flag, which stands for healthy, whereas the unusable signals are indicated as 
unhealthy with the “uh” flag. The unhealthy flag was set for some of the signals due to the 
observed transmitter instabilities, as explained in Section 3.3.