## 3 Proposed Deployment Methodology
### First Step: Deterministic Deployment  
Initially, a deterministic deployment is made by locating sensor nodes in predetermined locations in the mine. The sensor nodes are deployed in the RoI, specifically at tunnel crossings, tilt changes, work faces, and portals. The software tool reads an Excel file that contains the coordinates (\(x\) and \(y\) axis), the ground elevation, and the convention per each change in the terrain, e.g., portal (PT), tunnel (TN), and level (LV), or creates the structure from a blueprint image. These data are obtained from total stations. With these data, the software tool constructs the initial blueprint in 2D, locating sensor nodes in the predetermined locations. Table 2 shows the template used to construct the deterministic deployment. The cX col contains the x coordinate, cY contains the y coordinate, and cZ is the ground elevation. All parameters are in meters. Per each change in the ground elevation, one sensor is located due to changes in slope, which weaken signal propagation. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No.** & **cX (m)** & **cY (m)** & **cZ (m)** & **Convention** \\ \hline
1 & 1,024,819,6 & 1,067,344.7 & 2892 & PT \\
2 & 1,024,819.6 & 1,067,344.7 & 2880 & TN \\
3 & 1,024,827.4 & 106,323.1 & 2802 & TN-I-LV1 \\
4 & 1,024,889.5 & 1,067,149.4 & 2802 & LV1-G1 \\
5 & 1,024,928.5 & 1,067,175.5 & 2803 & LV1-G2 \\
6 & 1,024,955.1 & 1,067,193.0 & 2803 & F-LV1 \\ \hline \hline \end{tabular}  
* Conventions: PT: portal; TN: main tunnel; E: level initial; F: level final; and G: gallery.  
\end{table} 
Table 2: Template with coordinates obtained from the total station. However, according to normativity, the user can place other nodes if required. In Colombia, it is mandatory to implement a continuous system to monitor methane in coal underground mines with a high content of grisu gas (category III). Decree 1886/2015 defines three types of underground coal mine regarding the methane concentration [48]:  
* Category I: underground workings for which the methane concentration at any site in the mine does not reach zero percent (0%). * Category II: underground workings for which the concentration of methane at any site in the mine is equal to or less than 0.3%. * Category III: underground workings for which the methane concentration at any site in the mine is more significant than 0.3%. The monitoring system should be implemented in portals, work faces connected to the mine ventilation circuit, and roadways. In addition, it is mandatory to implement a carbon monoxide and oxygen monitoring system at work faces; underground sites with the presence of specialized electric systems, communication systems, and underground electrical substations; vehicles and personnel roadways; communications with old or abandoned works; and close to partitions that isolate burned areas [49]. The distance and location are evaluated to insert nodes in the network, as shown in Algorithm 1. The location refers to the nodes being at the same level or tunnel. Thus, it is necessary to calculate the Euclidean distance between a source node and a destination node. Then, it is determined if there is communication between the sensors according to the communication range (35 m) and, therefore, network connections. The sensing range (12 m) is used, too, to establish coverage areas. Subsequently, the algorithm evaluates if sensors can communicate with their neighborhoods. This evaluation is according to the distance and the location. Figure 3 shows the deterministic deployment in a medium-sized mine. The algorithm adds one sink node in the portal and, in this case, adds fifteen nodes distributed in crossings and slope changes. Figure 3: Deterministic deployment. On the other hand, the same evaluation is carried out with the coverage range. The results are stored in the distance matrix and the connection matrix. The distance matrix contains the distance between connected sensors, and the connection matrix shows if a connection between sensors exists.