## 3 Results
### Systematic Content Review Results for Sensors Monitoring Mine Tailings Storage Facilities  
#### 3.3.1 Content-Based Data Perspective Analysis  
In this chapter of this systematic review, the answers to the research questions, determined through an exhaustive content analysis of the 52 selected articles, are presented. The main engineering disciplines where sensors are used to monitor TSFs are represented in Figure 13. The most prominent of these engineering disciplines are geotechnics, mining, and civil engineering, with 10, 8, and 7 documents on these topics, respectively. As Figure 13 shows, geotechnics, mining, and civil engineering represent more than 50% of the analyzed documents. Conversely, structural engineering, geodesy, hydraulics, costs, electrical engineering, computer engineering, mechanics, and seismology each represent only one document. Three of the study documents do not specify any engineering discipline. Figure 14 depicts the timescale of sensor data collection, considering automatic data collection as real-time and manual data collection as not real-time measurements. The graph shows that of 47 documents, the data are predominantly automatically collected in real time; only one document reports manual, non-real-time data collection, and two documents do not specify a data collection timescale. Figure 14 shows the main applications of sensors in TSF monitoring, highlighting the modern trend of making real-time automatic measurements (90% of sensor usage). The space scale of data measurements performed with sensors (remote or on-site) for monitoring TSFs is represented in Figure 15, which shows that the most common method is remote measurements at 67% of the analyzed documents. Figure 14: Timescale used to record measurements from sensor technologies used to monitor tailings storage facilities. Figure 13: The main engineering disciplines where sensors are used to monitor tailings storage facilities. Figure 15 shows the main applications of sensors for tailings storage facilities monitoring, highlighting 35 mentions of remote measurements, 15 mentions of on-site measurements, and 2 documents that do not specify. The graph in Figure 16 depicts the different types of sensors used for monitoring tailings storage facilities according to the analyzed literature: Water level sensors (piezometers) lead the count with 8 mentions, followed by pressure sensors with six mentions and displacement sensors with 5 mentions. According to the information presented in Figure 16, there is a tendency to monitor aspects related to dams' physical stability, such as the key infrastructure of a TSF. Only 3 documents do not mention the type of sensors used. Several types of sensors are mentioned only once, such as InSAR, radar, UAVs, air quality sensors, and others. The type of data transmission implemented for sensor connectivity to monitor mine TSFs is shown in Figure 17. The three main types of data transmission are satellite (11 applications), Zigbee (eight applications), and 4G (mobile cellphone) with 6 applications, all wireless connection formats. Notably, among the data presented in Figure 17, 5 documents do not specify the connectivity technology used. Figure 16: The type of sensor technology used to monitor tailings storage facilities. Figure 15: Space scale of data measurements performed with sensors to monitor tailings storage facilities. The use of cables or wireless systems for sensor connectivity is shown in a pie chart in Figure 18. Wireless systems are mentioned in 35 documents and wired systems are mentioned in 7 documents; 10 documents do not specify the system type. To transmit the information captured by a sensor or monitoring system and make it available in real time, some communication system technologies stand out. * Fiber optic and/or coaxial cable. Communication systems based on fiber optics and/or coaxial cable have been used routinely in the telecommunications and mining industries.