## 3 Satellite Signal Measurements in Various Weather Conditions
### Measurements, Data Conversion Techniques  
The measurement plan assumed 20 measurement days. Selected days were not consecutive, as different space and weather conditions were to be taken into account, but all of them occurred between October-December 2021. Once a day, GNSS data were collected using a satellite receiver. Every day, the necessary information about the external environment conditions was recorded, such as air temperature, humidity, wind speed, atmospheric pressure, and type of satellite systems used/satellites visible (see Section 3.2). Additionally, solar activity was recorded [57]. Measurements were conducted based on the absolute method, using one receiver and the satellite systems. The following steps (described in detail in the subsequent paragraphs of this chapter) of the data analysis procedure for each measurement were implemented:  
1. Data aggregation, geographic coordinates determination at each measurement point;
2. Conversion of coordinates from World Geodetic System-84 (WGS-84) to flat Coordinate System 1992;
3. Calculation of the traveled trajectory in two directions: north-south, east-west, trend line, and its mathematical equation setting;
4. Determination of the arithmetic mean (in each direction), as well as the standard deviation;
5. Analysis, repetition of the procedure for subsequent measurements. Ad 1. The receiver used was GPS UBLOX \"P031717\" receiver [58] (see Figure 1), which allows the recording of real-time trajectory traveled with the device. It is equipped with a GNSS module and may have an antenna attached. Every measurement was conducted on a straight road. The measurements were saved by the u-center software [58] in ubx format, an intuitive and easy-to-use application (see Figure 2). It contains many functions, such as a map of deviations, the ability to observe satellites' position and their signals' strength, as well as a compass or speedometer, for example. In addition, during real-time measurements it is possible to read the current latitude, longitude, altitude above the sea level, and DOP values. After necessary conversions, it was possible to specify the number of satellites that were visible to the receiver during the measurements as well as from which satellite system they came from. Furthermore, signal strength, DOP factors, geographical coordinates, and altitude above sea level could also be determined. In order to analyze the measurement results, it was decided to determine the measurement uncertainty related to the course of the distance measured by the satellite receiver. Ad 2. Geographical coordinates of each measurement needed to be converted from World Geodetic System-84 (WGS-84) to flat Coordinate System 1992 in order to obtain the north-south and east-west directions (with assigned specific time). The coordinate conversion tool, available on website [59], was used to fulfill the task (see Figure 3). The input data represent geographic coordinates from the receiver, with the first number for longitude and the second for latitude. The output data show the x, y coordinates properly converted from the input data. Figure 1: GNSS receiver used. Figure 2: U-centre software interface. Ad 3. Thanks to the x, y data obtained (Table 1), it was possible to calculate the travelled trajectory in two directions: north-south, east-west. At the same time, the trend line and its mathematical equation was set. Trend lines and their mathematical equations are presented on Figure 4--Equation (5) and Figure 5--Equation (6):  
\[y=-0.0022x-2579.5 \tag{5}\]  
\[y=-0.0001x+4104 \tag{6}\]  
Figure 4: Geographical coordinates conversion, y axis. \begin{table}
\begin{tabular}{c c c} \hline
**Time [s]** & **y [km]** & **x [km]** \\ \hline
0 & \(-2579\),463661 & 4104,031343 \\
17 & \(-2579\),510050 & 4104,031565 \\
47 & \(-2579\),576051 & 4104,028103 \\
77 & \(-2579\),640251 & 4104,025706 \\
107 & \(-2579\),706555 & 4104,021771 \\
137 & \(-2579\),772036 & 4104,019176 \\
155 & \(-2579\),808401 & 4104,013526 \\ \hline \end{tabular}
\end{table}