# Analysis of the Impact of Multipath on Galileo System Measurements
## 4 Multipath Analysis
### Phase Multipath Analysis
Identical STD values of 2.3 mm were obtained for the E1 Galileo and L1 GPS observations. Despite slight differences in carrier wavelengths for the individual components of the Galileo E5 band, an identical STD value of 3.2 mm was obtained for all of these observations. On the other hand, for GPS observations at the L2 frequency, different values of the multipath impact were obtained, but the difference may be due to the specific nature of L2W signal tracking. For a satellite elevation of 50\({}^{\circ}\), the multipath impact on the phase observations is at the level of 1 mm. Figures 10 and 11 show the time series of CMC combinations and DD phase residuals for given satellites (in the case of DD, the analyses concern non-reference satellites) as well as signal scalograms, obtained as a result of the performed wavelet transform. In order to facilitate comparisons, the time shown on the horizontal axis of the visualization refers to the duration of the respective observation series, as the observations of the two satellites refer to different times of day. The time-series diagrams additionally show the elevation of a given satellite. Next, using a feature of the multipath effect related to the characteristic periodicity of its impact, the signals were decomposed and reconstructed into components with frequencies typical for the phenomenon: from 0 to 3 mHz for specular reflections, from 3 to 20 mHz for diffuse reflections, and from 0 to 20 mHz for the whole range (see Figures 12 and 13). From the CMC scalograms, it can be seen that the observation series of both satellites show disturbances with similar characteristics at similar times, with frequencies of approximately 10 mHz, mainly in the initial part of the analyzed signals (i.e., for low satellite elevations). What is distinctive is also the disturbance that occurs between the 2400 th and the 3000 th seconds. It is worth noting, however, the presence of low-frequency components in the signal, at approximately 1 mHz, observed for up to about the 3000 th second. In the figures showing the extracted components of the signal, it is clearly visible that it is the components with higher frequencies that are characterized by larger amplitudes. The characteristics of individual disturbances for both satellites are very similar. Table 4 shows the maximum values of amplitudes for given components of the signal. It should be emphasized that these statistics concern only those fragments of observations when the satellite was observed at an elevation of at least 10\({}^{\circ}\) (the figures show the range of observations from an elevation of 5\({}^{\circ}\)). Thus, these amplitudes represent the maximum values of the observation errors due to the multipath effect for given signal reflections. It can be seen that the highest values of the multipath errors have been recorded for the whole frequency range characteristic for this phenomenon. The peak-to-peak amplitudes of the multipath error are equal to 1.094 m for Galileo E1 observations and 1.434 m for GPS C/A code. The impact of specular reflections in the examined case turns out to be more than two times smaller. The errors determined in this way are larger for the GPS signal in almost every case, which confirms the conclusions regarding the superiority of the Galileo code observations with respect to GPS. Figure 9: Skyplot for satellites E18 and G09. In the case of DD phase residuals, the signals are devoid of high-frequency components associated with measurement noise. The scalograms of the analyzed series show mainly two main components of these signals (see Figure 11). As in the case of CMC, these are components with frequencies of approximately 10 mHz, also occurring in the initial part of the signal, as well as components with lower frequencies of approximately 1-3 mHz, occurring for up to about the 3000 th second of the signal.