## 3 Sound Source Localization Fusion Algorithm of a Three-Plane Five-Element Microphone Array
### Outdoor Experiment  
The outdoor experiment was carried out on the upper floor aisle of School of Electronic and Information Engineering, Nanjing University of Information Science and Technology. On this occasion, the target of sound source localization was thunder source point. The outdoor experiment scene is shown in Figure 8.  
In Figure 8, the positive half of the x-axis and the y-axis of the three-plane five-element microphone array were respectively aligned in the south and east directions. With the help of the real-time data from the radar chart, the outdoor application effect of the fusion algorithm was analyzed. We set the array element spacing to 1.0 m and conducted two experiments to expect the algorithm to provide data feedback for thunderstorm cloud forecast warnings. The first experimental time was around 19:42 on 22 April 2019, and the data obtained by the fusion algorithm and the radar chart at this time are shown in Table 7 and Figure 9, respectively. The second experimental time was around 20:10 on the same day. Table 8 showed the measured results of the fusion algorithm, and Figure 10 was the real-time radar chart. In addition, the red cross marked in Figures 9 and 10 was the position of the measurement point. In Table 7, the coordinates of the thunder source measured by the fusion algorithm were (4.2 km, 24.1\({}^{\circ}\), \(-\)32.7\({}^{\circ}\)), the thunder source was about 32.7\({}^{\circ}\) west-south, and the elevation angle was relatively small, reaching 24.1\({}^{\circ}\). In addition, the thunder source was 4.2 km away from the array center. This indicated that at around 19:42, the unexpected data was measured by the microphone array due to interference from the external environment, and no thunder source occurred in the upper area of the array. In Figure 9, the radar echo intensity was about 10 dBZ, indicating that a small amount of charge was accumulated in the cloud layer above the array, and no thunderstorm cloud existed. In summary, at 19:42 on 22 April 2019, there was no thunder source generated at the outdoor test point, and the real-time measurement result of the radar chart was consistent with the results obtained by the fusion algorithm, indicating that the method has better application effect. Besides, based on the data of 4.2 km and \(-\)32.7\({}^{\circ}\), we can speculate that the thunderstorm cloud should be active nearby, which is likely to move from the southwest toward the test point. In Table 8, the thunder source point coordinates measured by the fusion algorithm were (1.4 km, 78.5\({}^{\circ}\), 46.9\({}^{\circ}\)). The thunder source was about 46.9\({}^{\circ}\) south by east, and it was only 1.4 km away from the array. In particular, the elevation angle was 78.5\({}^{\circ}\), which was almost perpendicular to the z-axis. At this time, it is considered that the thunder source had occurred in the upper area of the array. At this point, in Figure 10, the radar echo intensity exceeded 40 dBZ, indicating that a large amount of charge was accumulated in the cloud layer above the array, and there was indeed a thunderstorm cloud. In summary, at 20:10 on 22 April 2019, the thunder source was generated over the test point, and the measurement results of the radar chart were consistent with the results obtained by the fusion algorithm. This is a good illustration of the effectiveness of the algorithm, and this experiment also verified the prediction of the previous experiment. The fusion algorithm performs well in outdoor experiments, and the data measured by the algorithm can be consistent with the official radar data, reflecting its good overall performance. \begin{table}
\begin{tabular}{c c} \hline
**Data Source** & **Sound Source Spherical Coordinates** \\ \hline fusion algorithm & (4.2 km, 24.1\({}^{\circ}\), \(-\)32.7\({}^{\circ}\)) \\ \hline \end{tabular}
\end{table} 
Table 7: First experimental results. Figure 10: Radar chart displayed at 20:10.