Vision-Based UAV Navigation Using Multi-Intensity Illumination and Fiducial Markers in GPS-Denied Environments

In hazardous or restricted environments, such as tunnels, industrial facilities, or mountainous terrains, conventional inspection tasks pose significant risks. Leveraging the high mobility of unmanned aerial vehicles (UAVs), such tasks can be performed more safely and efficiently. While GPS provides reliable positioning in outdoor settings, its absence in GPS-denied environments presents substantial challenges for autonomous navigation. This study proposes a vision-based UAV navigation system utilizing fiducial markers and a multi-intensity illumination scheme to enable accurate localization in GPS-denied scenarios. The system operates through a three-stage guidance framework: long-distance, short-distance, and target-shift. A custom illuminator enhances marker visibility under varying lighting conditions, while the YOLOv5 model facilitates target recognition throughout the flight. As the UAV approaches the marker, the ArUco Marker-Based Positioning System (AMBPS) ensures precise positioning and stable hovering. Experimental results demonstrate that the UAV can successfully navigate from an initial position 50 meters away to the predefined location marked by the ArUco board. Across 120 recorded measurements, the system achieved a positioning error within ±0.15 meters. The core technique of this navigation framework has been patented under ROC Patent No. I862216.