## 2 Materials and Methods
### Data Capturing and Processing Software  
All 10 smartphones were equipped with the Android operating system in the latest version available for the respective mobile phone and with all current updates. However, the phones had different versions of the Android system and especially different filters integrated in the analysis of the GNSS raw data, which can affect the analysis of the data. In this study, GNSS NMEA data provided by the Android Location API are used. As part of the Android 6 ('Marshmallow') system, the Location API 23 allows access to the NMEAListener class, providing basic NMEA sentences used in this study. As part of the Android 7 ('Nougat') system, the Location API 24+ provides GNSS raw and computed \begin{table}
\begin{tabular}{c c c c l l} \hline \hline
**ID** & **Latitude** & **Longtitute** & **SP ID** & **FS** & **Conditions and Main Obstacle for Reception** \\ \hline
1 & 48.0651990 & 11.5655060 & 7935 0188 & B & Beech dominated mixed forest, 13 m to forest road, closed dense canopy, trees \textgreater{} 15 m \\ \hline
2 & 48.0502484 & 11.4392006 & 7934 0040 & B & Beech dominated mixed forest, 6 m to forest road, closed canopy with crown gaps towards the road, trees \textgreater{} 12 m \\ \hline
3 & 48.0499501 & 11.4425390 & 7934 0041 & B & Beech dominated mixed forest, 10 m to forest road, closed canopy, trees \textgreater{} 15 m \\ \hline
4 & 47.9962202 & 7.7610121 & 8012 031 & BW & Beech dominated deciduous forest, closed canopy, trees \textgreater{} 20 m \\ \hline
5 & 48.0378690 & 7.9720488 & 7913 163 00 & BW & Fir dominated mixed forest, northeast slope, closed canopy, trees \textgreater{} 30 m \\ \hline
6 & 48.0269512 & 7.9535119 & 7913 134 00 & BW & Beech dominated mixed forest, closed canopy, trees \textgreater{} 25 m \\ \hline
7 & 47.8880590 & 8.1546365 & 8114 034 & BW & Spruce, pure stand, medium dense canopy, trees \textgreater{} 25 m, natural rejuvenation \textgreater{} 4 m \\ \hline
8 & 47.8885525 & 8.1558580 & 8114 034 01 & BW & Spruce, windthrow area with large open sky areas, trees \textgreater{} 25 m \\ \hline
9 & 47.8907364 & 8.1619936 & 8114 269 & BW & Spruce, pure stand, 6 m to forest road, closed canopy with crown gaps towards the road, trees \textgreater{} 25 m \\ \hline
10 & 47.9650230 & 7.8463260 & 8013 025 & BW & Beech dominated mixed forest, northward slope, closed canopy, trees \textgreater{} 25 m \\ \hline
11 & 50.6989621 & 13.1634072 & 5244000100 & S & Spruce, pure stand, hilltop, canopy with greater gaps, trees \textgreater{} 20 \\ \hline
12 & 50.6971547 & 13.1657759 & 5244000101 & S & Spruce, pure stand, 2 m to forest road,closed, very dense canopy, crown gaps towards the road, trees \textgreater{} 12 m \\ \hline
13 & 50.7170483 & 13.1437748 & 5244002201 & S & Beech dominated mixed forest, closed canopy with small gaps, trees \textgreater{} 20 m \\ \hline
14 & 50.6900370 & 13.1400410 & 5344006100 & S & Spruce, pure stand, 4 m to forest road, closed canopy, crown gaps towards the road, trees \textgreater{} 25 m, \\ \hline
15 & 50.7026740 & 13.1225790 & 5244001201 & S & Spruce, pure stand, 5 m to forest road, closed canopy with crown gaps towards the road, trees \textgreater{} 25 m \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characteristics of the different study sites (SP ID: Official ID of the local survey point; FS: Location in federal state [B: Bavaria; BW:Baden-Württemberg; S: Saxony]). information via Android classes. Therefore, e.g., GNSS clock, receiver time, clock bias, received satellite time, and code- and carrier-phase data are accessible. The Location API 24+ is backwards compatible. Therefore, used functions, such as NMEA sentences, are also available in higher versions [75,84]. With the NMEA data provided by the smartphone's Android Location API, single point positioning (SPP) can be assumed for internal determination of the position. The app 'GPStest' from the developer 'barbeauDev' was used to record the GNSS data. The program code is open source and available on GitHub [85].