## 3 Materials and Methods
### Design, Implementation, and Installation of a Low-Cost GNSS Monitoring System
#### 3.3.2 GNSS Data Processing  
The processing of data from low-cost sensors took place using open source software from the \"RTKLIB\" library ([[http://www.rtklib.com](http://www.rtklib.com)]([http://www.rtklib.com](http://www.rtklib.com))). This software is installed both inside the minicomputer that transmits the RTCM stream of the uBlox receiver, and at the control center.  
In the control center, the STR2 STR program stores the RTCM flow received every second from the monitoring stations, in a data file packaged both hourly and daily. Even the automatic GNSS data processing techniques mainly refer to a series of RTKLIB free-use package programs as well as to some software, specifically built and necessary for these purposes, aimed at scheduling a different operation:  
1. Automatic data acquisition from Ublox single-frequency receivers;
2. Daily packaging of these data according to standard RINEX formats;
3. Data acquisition of real or virtual master stations for post-processing;
4. Automatic post-processing of the rover stations with master stations or with virtual stations for movement monitoring;
5. Post-processing of the data of stations close to each other, for deformation monitoring;
6. Automatic sending of a reasoned report of the post-processing results both via email and to web platform;
7. Construction of graphs of displacements and deformations and sending it specialized technicians to interpret the results.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Instrument** & **Unit Cost** \\ \hline GNSS uBlox EVK8T Receivers & 70 \(\upcels\) \\ Garmin antenna & 50 \(\upcels\) \\ Tri-axial accelerometer + temperature sensor & 150 \(\upcels\) \\ Micro PC mainboard, plastic box and dongle Wi-Fi & 200 \(\upcels\) \\ Installation cost & \(\approx\)500 \(\upcels\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Madonna del Sasso site. The unit cost of instrumentations and the estimate installation cost.  
Figure 6: The prototypal multisensor box and the Garmin Antenna. 1 = Micro PC mainboard, 2a = Dongle Wi-fi and relative antenna (2b), 3 = GNSS mass-market uBlox EVK8T Receivers, 4 = Power supply, 5 = Tri-axial accelerometer + temperature sensor, 6 = Garmin antenna.  
Another topic is the real-time transmission of data. Even if post-processing involves daily processing data, for which acquisition rates of 30 s are sufficient, data transmission in the RTCM 3.01 format at a rate of 1 s does not require special equipment. This can allow for post-processing as well as future real-time control. These files in RTCM format every hour and every day are converted into a RINEX format measurement file through the \"CONVBIN\" command. Finally, it is necessary to treat this data with the same periodicity; this is possible through the \"RNX2 RTKP\" command. However, differential post-processing requires the use of data from at least one master station. For the stations of Madonna del Sasso, the master station is the permanent station of Gozzano, about 9 km away. At the end of the conversion, and the differential processing in post-processing, the RINEX observation and navigation files must be compressed and archived. The results of the differential positioning come together in ASCII files. Finally, a file that contains a summary of the results of all daily treatments for all stations and for any treatment is created. Processing is considered to be failed if the complete fixing of the phase ambiguities, and the ratio test [32] is not achieved.  
Finally, a report is sent by e-mail of the daily post-processing outputs. This report is sent to people with expertise in GNSS processing and in landslide monitoring. These outputs and the statistical controls are also deposited in the cloud, together with the graphic drawings and the hourly processing reports.  
Alert information is provided through a table containing codes similar to traffic light signals, which will be described later.  
All these commands are scheduled on the computer and are completely automatic.