Enhancing Uncrewed Aerial Vehicle Techniques for Monitoring Greenhouse Gas Plumes at Point Sources

The urgency of the global climate crisis necessitates advanced monitoring of greenhouse gases, with an emphasis on capturing their spatial and temporal variability. This study explores techniques to enhance plume detection and concentration measurements using uncrewed aerial vehicles (UAVs) for monitoring at point sources, specifically at an incineration stack. Through preliminary site investigations, our approach employed strategically designed flight paths and an autopilot system to optimize flight operations within the constraints of limited flight time due to battery capacity. We combined a UAV-mounted anemometer with a plume rise model to localize the plume center at a distance of 30 m from the stack center and evaluated its performance by comparing the model-based estimations at different altitudes and angular directions with the observation results. The comparison demonstrated that the results obtained by localizing the plume center using a plume rise model and a UAV-mounted anemometer aligned well with observations based on CO₂ concentration analysis. The comparative analysis showed a RMSE of 8.44 m and a MAE of 7.26 m for altitude, and a RMSE of 32.31${}^{\circ }$ and a MAE of 25.78${}^{\circ }$ for angular direction. Furthermore, we assessed the effectiveness of hovering UAV flights, in which a UAV remains stationary at a fixed point in the air, compared to non-hovering flights in capturing pollutant concentration. While both methods performed similarly in detecting the plume center, non-hovering flights underestimated the CO₂ concentration due to insufficient time for measurement despite a sensor response time of less than three seconds. Overall, our proposed hybrid monitoring strategy integrates non-hovering and hovering flights, enhancing both plume detection efficiency and concentration measurement accuracy at point sources.