## 4 Results
### GNSS Data Processing: Quality and Reliability
#### 4.2.2 Alert Assessment Based over a Long-Term Period Trend  
Another automatic control made by the algorithm is searching for anomalous acceleration trends in a long-term period. In this case, an alarm must be provided if the displacement rate, calculated from the linear regression, exceeded fixed ST and GT. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Alarm** & **Alarm** & \multicolumn{3}{c}{**Number of Alarm**} & \multicolumn{3}{c}{**\% of Alarm**} & \multicolumn{3}{c}{**\% of Fixed Alarm**} \\ \cline{3-11}
**Color** & **Code** & **E** & **N** & **h** & **E** & **N** & **h** & **E** & **N** & **h** \\ \hline Not Fixed & 0 & 37 & 37 & 37 & 22\% & 22\% & 22\% & - & - & - \\ Green & 1 & 127 & 127 & 120 & 77\% & 77\% & 72\% & 98.5\% & 98.5\% & 93.0\% \\ Yellow & 2 & 2 & 2 & 2 & 1\% & 1\% & 1\% & 1.5\% & 1.5\% & 1.5\% \\ Red & 3 & 0 & 0 & (7) & 0\% & 0\% & (4\%) & 0\% & 0\% & (5.5\%) \\ Validated & - & - & - & No & - & - & No & - & - & No \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The alarm code for East, North, and vertical components the for the period December 2018–May 2019 for the GNSS SAS a. After having computed the parameters of the trend line, the statistical significance of the velocity is calculated using a probability value setting parametrically. This value is set at 90%, and this means that the measurement must be with low noise from the regression line to avoid to have spike measure. The software procedure, developed in Matlab language, also calculates the absolute value of this speed, using as an index the number of millimeters of displacement every hundred theoretical days of measurement. In addition, in this case, a vector of three components is written in an output file and, for each baseline, indicates with zero the non-significativity of the estimate speeds. A value not equal to zero, with the sign, indicates that the speed in mm/100 days on that coordinate. Any speed that, in absolute value, does not exceed 3 mm/100 days is considered non-significative, based on the results of topographic monitoring and Colombero studies. In addition, this parameter and the probability value of significance are variable parametric indices. The preliminary results of GNSS monitoring have too short temporal time series to make a reliable analysis. In further studies, it would be possible to analyze the entire seasonal cycle. Figure 11 shows an example of the daily automatic output of GNSS processing: Figure 11A shows graphs of displacement time series of one of the two stations of Madonna del Sasso (SAS b). In Figure 9B, we see the time series of the deformations. For deformation, we intend the difference of displacement between the two stations, both placed on the Madonna del Sasso landslide (SASa-b). All the graphs are also located daily in the shared Google Drive directory and a daily email that contains the link to a shared cloud directory and sends an ASCII file of the \"traffic light\" synthesis to geologists specialized in deformation analysis. The short-term analysis of displacement did not show critical acceleration, and the movement is all inside the noise (2\(\sigma\)) of the measurements. Also, the short-term GT was not yet defined as the more extended time series of data is necessary. Even if the long-term displacement has too short temporal series (less than half seasonal cycle) to make reliable interpretation of data, we try to make a preliminary analysis of available data (December 2018-June 2019) and a comparison with ARPA Piemonte topographic measurements (T2 benchmark). Unfortunately, lighting damages limited the possibility to have a more extended and continuous GNSS time series. In the figure (Figure 12A), it is possible to see that the period of continuous GNSS measures only one interval between two topographic measures. Despite the short period of measure, the magnitude of planimetric displacement is similar. Figure 11: An example of displacement and deformation time series output sent to a monitoring expert.