Performance of UAV-based airborne gamma-ray spectrometry for wide-area radiation monitoring of contaminated sites

This study presents the development and field validation of a UAV-based airborne gamma-ray spectrometry system (MARK-M1), designed by the Korea Atomic Energy Research Institute for rapid radiological assessment in post-accident scenarios. The MARK-M1 integrates two LaBr₃(Ce) detectors, global positioning system, and a laser altimeter, with data transmission ensured via Bluetooth communication. Field surveys were conducted in collaboration with the Japan Atomic Energy Agency around the Fukushima Daiichi Nuclear Power Plant. An attenuation correction factor was derived from hovering flights at multiple altitudes and applied to convert aerial measurements to dose rates at 1 m above ground level. The results showed that flight speed had little effect on dose rate estimation when appropriate detector sensitivity and flight line spacing were ensured. However, in low-lying areas with sloped terrain, significant discrepancies were observed between airborne and ground-based measurements, indicating the limitations of flat-ground assumptions in attenuation models. Incorporating terrain data such as digital elevation models is suggested to improve estimation accuracy in complex topographies. These findings demonstrate both the practical utility and necessary refinements for UAV-based gamma-ray surveys in real-world emergency response applications.