## 3 Satellite Signal Measurements in Various Weather Conditions
### Changing Weather Conditions during the Measurements  
For each measurement, which means every day, the necessary information about the external environment conditions was recorded, such as air temperature, humidity, wind speed, atmospheric pressure, type of satellite systems used/satellites visible, and solar activity (Table 5). Weather conditions were independent of the receiver's operator. To introduce even more variety, the measurements were conducted during various moments of a day: from morning until late at night, which was operator-dependent. Temperature conditions varied from 3 \({}^{\circ}\)C in one evening to 15 \({}^{\circ}\)C, while the measurement was conducted at noon. Based on the measurement performed, it is difficult to draw a precise conclusion regarding temperature influence on positioning error. The pressure varied from 996.36 hPa during one evening measurement, up to 1018 hPa on a forenoon. Humidity was the lowest during measurement no. 12, recorded as 55.4%. This was also the measurement during which the temperature reached the highest value. Humidity was the highest during measurement no. 8, reaching 97.13%, when the pressure also reached the highest value of all. The wind speed was noted from 0.8 m/s up to 5.83 m/s. However, in the authors' opinion, wind strength is dependent on the daytime moment (stronger in the forenoon and weaker in the evening). During one half of the measurements, all satellite systems were available. That is positive. In six cases, satellites from only one satellite system (out of four) were visible to the receiver. For the three measurements (nos. 6, 8, and 14) where it was impossible to obtain required data, only one satellite system was available, and it was always Galileo. What requires additional explanation to sum up the discussion on Table 5 is the last (but not least) column--solar flares. Solar flares are huge explosions on the sun that release energy, light, and high speed particles into space [61]. Adopted classification system divides solar flares according to their strength, based on their brightness in X-rays, measured in W/m\({}^{2}\), and in the band from 0.1 up to 0.8 nm. The smallest ones are A-class (near background levels), then B, C, M, and X. Similar to the Richter scale for earthquakes, each letter represents a ten-fold increase in energy output (is 10 times stronger than the previous one). Therefore, an X is ten times an M and 100 times a C. Moreover, within each \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**No** & **Daytime** & **Temp.** & **Pressure** & **Humidity** & **Wind** & **Satellite Systems** & **Solar Flares** [57] \\  & & [\({}^{\circ}\)C] & **[hPa]** & **[\%]** & **[m/s]** & **Satellite Systems** & [57] \\ \hline
1 & Afternoon & 12 & 997.6 & 58 & 3.61 & All & B9.5 G2 \\
2 & Afternoon & 11 & 1002.9 & 68 & 3.33 & All & C1.3 Kp3+ \\
3 & Forenoon & 8 & 1008.4 & 77 & 2.78 & All & C2.2 Kp2+ \\
4 & Forenoon & 10.2 & 1005.8 & 83.5 & 5.83 & GPS & B1.6 Kp3 \\
5 & Evening & 7 & 1007.3 & 92 & 2 & GPS & B1.6 Kp3 \\
6 & Evening & 8.5 & 1010.5 & 92.5 & 3.2 & Galileo & B4.8 Kp2+ \\
7 & Evening & 3 & 1013.5 & 96.8 & 2.3 & All & B6.3 Kp2\(-\) \\
8 & Forenoon & 3.5 & 1018 & 97.13 & 2.1 & Galileo & B6.2 Kp2\(-\) \\
9 & Evening & 3 & 1017.9 & 97 & 0.65 & Glonass BeiDou & B6.2 Kp2\(-\) \\
10 & Night & 4 & 1008.6 & 91 & 2 & All & C8.5 Kp2+ \\
11 & Evening & 7.5 & 1005.3 & 85.1 & 1.8 & Without BeiDou & M1.5 Kp1+ \\
12 & Noon & 15 & 1005.2 & 55.4 & 3.8 & Without Galileo & M1.5 Kp1+ \\
13 & Night & 12 & 1001.6 & 70 & 3.5 & Glonass & C3.9 Kp4- \\
14 & Morning & 10 & 1003.95 & 80 & 2.4 & Galileo & C3.2 Kp4 \\
15 & Evening & 6.1 & 996.36 & 97.1 & 1.8 & All & C5.3 G2 \\
16 & Forenoon & 9.2 & 1010.8 & 87.2 & 5.2 & Without Galileo & C1.7 Kp4 \\
17 & Night & 8.5 & 1009.5 & 82.3 & 4.8 & All & C1.7 Kp4 \\
18 & Morning & 5.2 & 1008.2 & 96.99 & 2.1 & All & M1.5 Kp1+ \\
19 & Evening & 15 & 999.2 & 95.6 & 0.8 & All & C7.4 Kp4+ \\
20 & Evening & 15 & 999.2 & 95.6 & 0.8 & All & C7.4 Kp4+ \\ \hline \hline \end{tabular}
\end{table}