Unmanned aerial vehicles ("drones") as tools for small scale radiometric surveys

Abstract

An UAV has been developed by the Federal Office for Radiation Protection (BfS) and tested in the Chernobyl exclusion zone in September 2016. A commercially available hexacopter has been equipped with a 1.5 cm3 CZT gamma spectrometric detector (μSPEC), GPS, data processing unit (Rasperry PI with Linux) and Wi-Fi for data transmission to the ground base. Optionally a camera can be carried. The system records gamma dose rate every 2 seconds and gamma spectra every 10 minutes. The total cost of the system is significantly below 10k€ which includes the detector (6k€), data acquisition system (0.2k€) and the UAV (1.2k€). The system is very mobile, easy to set up and to operate in the field. Results are plausible and easy to interpret, spatial resolution of the gamma dose rate on the ground is surprisingly high. Measurement results from the Chernobyl exclusion zone show that the sensitivity of the detector allows radiation survey in areas where the dose rate level is above 0.3 μSv/h. Limitation of the small system are the relatively short operation range of a few 100 m and the lack of an altimeter to assure constant flight altitude above ground. Among the results of the exercise were that a high gamma dose rate gradient in the field can be well identified and the observation that the measured gamma dose rate depends relatively little on the flight altitude between 3 and about 15 meters above ground, for a large scale contamination field. As a conclusion, the use of UAVs for radiometric surveys is a promising and viable complement to traditional air-borne reconnaissance for small areas, and an alternative to ground-based surveys in case of high radiation levels or difficult access.