# An Internet of Things (IoT) Application on Volcano Monitoring
## 4 Results and Discussion
### Data Records
First of all, drained batteries were replaced by 3.7-V non-rechargeable batteries, whose range of operation was more suitable for this application (Table 4). Then, in order to improve the batteries' cooling, they were changed in thermometers T2 and T8 from their initial position (Figure 4) to the top of the PVC tube. In addition, a thermal insulator was placed at half height inside the tube to reduce the heat transmission from its bottom. After these changes, T8 was poorly sealed, allowing water to filter inside the PVC tube, deteriorating the electronics little by little. This thermometer began to show a malfunction two months later, failing to acquire temperature values and showing some communication issues (which increased the error percentage in the T8 packets reception, Figure 18), until it finally stopped working. With regard to the rest of the network, it became fully operational again, and since then, data has been recorded without problems thanks to favorable weather conditions (Figure 13). Figure 17 and Table 8 show the RSSI levels of each thermometer measured at the repeater side. In general, RSSI levels remained quite stable and above the sensitivity limit of \(-123\) dBm according to LoRa parameters of the repeater-thermometer link (SF = 7 and BW = 125 kHz). However, Figure 16 displays different periods in which, due to the worsening of the weather conditions, a drop in the RSSI levels associated with a decrease in signal strength takes place. If high signal attenuations occur, these can lead to interruptions in the operation of the network (grey dashed rectangles in Figures 13 and 14). As these conditions gradually improve (possible ice sheets melted, visibility between devices was greater, etc. ), the network recovers and continues with normal operation (red rectangles in Figure 17). An estimation of the error in the reception of each thermometer packages was done computing the received and theoretical received packages ratio as follows:  
\[\text{ERROR}=\ 1-\frac{NRM}{TNM}\cdot 100\% \tag{2}\]  
Where NRM stands for the Number of Recorded Measurements in a specific time period, and TNM stands for the Theoretical Number of Measurements in the same period. Equation (2) was applied  
Figure 17: RSSI levels of each thermometer in areas A and B measured at the repeater side. Red rectangles point out periods in which the reception of packets in the repeater gets worse due to adverse weather conditions. to the period of time in which all the thermometers have been working, and the results were plotted in Figure 18.  
T2 and T8 percentages of error in 24 h are the highest ones due to the problem with batteries already mentioned. The percentages of transmission errors of the remaining thermometers were quite low (below 2% in 24 h). A percentage of error so low allows to maintain a suitable temperature sampling when the weather conditions are sufficiently favorable, revealing the robustness of the designed network. Differences between thermometers were due to the different characteristics of the sites in which they were settled, the weather conditions, the distance to the repeater, whether there was direct vision with the repeater or not, and the incidence of the sun (related to the melting of the ice that could form).