# Wind Source Localization System Based on a Palm-Sized Quadcopter
## 4 Wind Source Localization Experiment
### Experimental Results  
The trajectories of each scenario are depicted in Figure 5a-c. Figure 5a-c correspond to Scenarios 1-3, respectively (see Supplementary videos). We indicate the start and end positions of WSL using \"\(\blacksquare\)\" and \"\(\bullet\)\", respectively. The red areas in Figure 5a-c represent the goal areas, while the blue and black lines denote successful and failed localizations, respectively. The trajectory shows that in Scenario 1, the quadcopter moved to various places and exceeded the time limit in most cases. In Scenarios 2 and 3, while instances of incorrect movements occurred, the quadcopter was confirmed to move upwind direction in most trials. To statistically evaluate these trajectories, the localization success rates, localization times, and upwind movement selection rates (hereafter referred to as upwind rates) for 10 repeated experiments in each scenario are shown in respective Figure 6a-c. The localization success rate was 0% in Scenario 1. In Scenarios 2 and 3 with environmental winds, success rates were 70% and 90%, respectively, indicating a higher success rate under the stronger environmental wind conditions of Scenario 2. Significant differences between Scenarios 1, 2, and 3 were observed in localization success rates ([PERSON]'s exact test, \(p<0.05\)). The calculations of localization times for successful localizations in Scenarios 2 and 3 showed no significant difference despite variations in environmental wind strength. Thus, we found no significant increase in localization time due to reduced movement speeds influenced by environmental winds (Wilcoxon rank-sum test, \(p<0.05\)). The degree to  
Figure 4: The environment of the wind source localization experiment. (**a**) Schematic diagram of the experimental field. (**b**) Flow for constructing wind speed distribution. (**c**) Wind speed distribution for Scenario 2 (low wind speed). (**d**) Wind speed distribution for Scenario 3 (high wind speed). which the quadcopter selects to move upwind during the localization behavior is evaluated by comparing the upwind rate. The upwind rate is calculated as follows:  
\[\text{Upwind Rate} = \frac{\text{Upwind movement}}{\text{All movement}}. \tag{1}\]  
The calculation of the upwind rate based on this equation showed a significant difference between environments with no wind and those with environmental wind. However, no significant difference was observed between Scenarios 2 and 3, confirming no significant change in behavior selection with the strength of the environmental wind (Steel-Dwass test, \(p<0.05\)). Overall, these results confirm that even under the low-speed conditions of Scenario 2, the quadcopter could extract only the ambient wind from the wake and move in the upwind direction. The trajectory in the windless condition of Scenario 1 shows that the quadcopter always moves randomly because it cannot detect the ambient wind, and the search fails because the quadcopter moves out of the search area. This indicates that the combination of the wind direction sensor arrangement and the anemotaxis algorithm can be used to detect the ambient wind and localize the wind source. Next, we analyzed the wind direction sensor values during WSL. Figure 7a shows histograms of wind speed values measured in 10 repeated experiments for each scenario. The blue lines in Figure 7a represent the thresholds for calculating the mode of wind speeds. The different colors in the histograms represent each scenario, illustrating varying distributions of measured wind speeds under different wind conditions. Even in the windless condition (Scenario 1), slight wind speeds were measured due to wake effects, suggesting that threshold processing suppressed anemotaxis behavior, resulting in random behaviors. Additionally, rose plots of measured wind direction values are shown in Figure 7b-d. The amplitude of the rose plots represents occurrence frequencies,  
Figure 5: Trajectory of wind source localization experiments (see Supplemental Videos).