Fluorescence-based detection of field targets using an autonomous unmanned aerial vehicle system

Abstract

Here we describe a proof-of-concept autonomous unmanned aerial vehicle (UAV) system that utilizes the fluorescence characteristics unique to different materials to scan and acquire targets in the field that includes fossils, rocks and minerals, organisms and archaeological artefacts. This is possible because these targets are often highly fluorescent against lower fluorescence backgrounds and may exhibit different colours. To detect these targets from a moving UAV, we utilize laser-stimulated fluorescence. This involves an intense laser beam that—unlike regular UV light—can project greater distances and generate sufficient fluorescence for targets to be detected on the UAV camera many metres above the ground. The system involves a lightweight UAV programmed to fly a waypoint pattern autonomously at night over the area of interest. LIDAR maintains its height above the terrain. A near-UV laser is projected across the ground as a horizontal line directly below the UAV. Co-mounted with the laser is a small highly sensitive video camera stabilized on a motion-controlled gimbal that records the laser line during the flight. An intermittent, powerful white light strobe flashes during the flight to record the UAV's ground position in the scanned area. The UAV returns with the laser video at the end of each autonomous mission. This video is post-processed, extracting the laser line data into a long continuous scan image showing the fluorescing ground targets. Initial analysis determines what colour the targets fluoresce so that a specific colour range can be extracted from the image to identify the locations of the detected targets. The white light strobe images are then used to quickly follow-up on the detections. This system holds the promise of becoming the lowest ‘ground truth’ layer in the mix of high-altitude map data produced by satellite- and airplane-based Geographic Information Systems. With centimetre resolution and the geochemical differences shown via fluorescence, this system will increase the scale and efficiency of data collection involving fossils, rocks and minerals including mineable materials, fluorescent organisms including biogenic mineral producers like shellfish as well as archaeological artefacts. Thus, the fields of evolution, ecology, Earth and planetary science, archaeology and other subjects involving fluorescent targets would all benefit from this new system.