# Noises in Double-Differenced GNSS Observations
## 3 Data Description  
The ZB DD observation combinations were derived using the GNSS measurements from reference station WUT1, which is situated on the roof of the Main Building of the Warsaw University of Technology (approx. location: 52\({}^{\circ}\)13\({}^{\prime}\)15\" N, 21\({}^{\circ}\)00\({}^{\prime}\)37\" E, see Figure 1). The Multi-GNSS measurements from the GPS, GLONASS, and Galileo systems, including the code and carrier phase observations on the L1, L2 and L5 bands, were carried out for the 0\({}^{\circ}\) elevation mask and 1 Hz interval using two identical Trimble R9s receivers connected to a single Leica Choke-Ring AT504 antenna through a GNSS signal splitter. The observations covered seven subsequent daily sessions for the year 2019, DOY: 055-061. A detailed description of the observed signals is presented in Table 1.  
The noise parameters of the individual GNSS observations were determined based on the ZB DD combination during a daily regime, obtaining seven independent sets of results. The mean values for the weekly solution were presented as the final values of the derived variance, autocorrelation, modified Allan deviation, and spectral indexes based on the linear regression of the Lomb-Scargle periodograms. Figures 2 and 3 present the noise statistics for one daily solution (2019, DOY:055) for the code and carrier phase observations for all of the satellites. The results are presented using a box plot, where the median is indicated as a central mark in the box, and the 75 th and 25 th percentiles of the errors are marked as the top and bottom edges of the box, respectively. The whiskers indicate the most extreme values, omitting outliers with a confidence level of about 99%. \begin{table}
\begin{tabular}{c c c c} \hline \hline
\begin{tabular}{c} **System/** \\ **Observation Type** \\ \end{tabular} & **L1** & **L2** & **L5** \\ \hline GPS & C1C/L1C & C2L/L2L C2W/L2W & C5Q/L2Q \\ \hline GLONASS & C1C/L1C C1P/L1P & C2C/L2C C2P/L2P & \\ \hline Galileo & C1C/L1C & & C5Q/L5Q C7Q/L7Q C8Q/L8Q \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Types of the observations used for the analysis for each GNSS system (notation according to RINEX 3.04 format [54]). Figure 1: GNSS reference stations on the roof of the Main Building of the Warsaw University of Technology—WUT1 station on the right side. The statistics for the mean weekly solution are presented in Table 2. The results show that there is a large amount of variation in the measurement noise level depending on the GNSS system and type of observation. For the code measurements, the GLONASS C1C and C2C signals are characterized by the highest noise, with standard deviations of \(\pm\)0.89 m and \(\pm\)0.44 m, respectively. On the other hand, the Galileo C7Q and C8Q and GPS C5Q observations have the lowest noise level, not exceeding \(\pm\)0.10 m. For the carrier phase measurements, the variability is smaller, and the noise level ranges from \(\pm\)1.5 mm for the GPS L1C and Galileo L1C observations to \(\pm\)3 mm for the GPS L2W and GLONASS L2C observations. For all of the observations, the mean value is very close to zero. However, it should be remembered that the presented standard deviation values refer to the double-differenced observations, which are increased in relation to the undifferenced observations by a factor of 2 and decreased by the common antenna LNA noise for the zero-length baseline configuration. The repeatability for the mean obtained from processing of the seven daily sessions did not exceed \(\pm\)3 mm for the code observations of \(\pm\)0.001 mm for the carrier phase observations, proving that the consistency of the daily solution is very high. A lower weekly repeatability at the level of \(\pm\)0.08 mm was only obtained for the GLONASS carrier phase L2C and L2P observations.