USING UAV-COMPATIBLE GAMMA RAY SPECTROMETRY TO MAP VARIABILITY OF SOIL RADIONUCLIDES

The Kentucky Geological Survey is using a UAV-compatible gamma-ray spectrometer to map local variability in soils and near-surface earth materials. The first application for this effort is to investigate potential microzonation of Kentucky soils for radon hazard assessments. Gamma-ray spectrometry detects the incidence of gamma ray photons, and because of the energy associated with the photons, decay of specific radionuclide species can be inferred. Traditional airborne GRS surveys are conducted from fixed wing aircraft or helicopters with shielded detectors pointing both up (to detect atmospheric radiation levels) and down (to detect ground-sourced photons). Because of the altitude and duration of typical traditional airborne surveys, data must be post-processed to account for cosmogenic contributions, atmospheric radiation, Compton collision effects, and altitude attenuation. Typical best-case resolution of resulting data is on the scale of 100m to 200m. Because of the weight constraints of a UAV compatible system, shielding is not an option, so the detectors are omni-directional. The relatively low altitude (<40m, typically much less) and short duration of UAV flights (<20 min with the current KGS system) mean that several of the considerations in traditional airborne surveys are either less of a factor or cannot be isolated in the available data. As a result, footprint of observation and altitude attenuation are the primary processing considerations. Resolution of 2m to 20m can be achieved with careful and low-altitude data collection. Care must be taken to understand the range of possible gamma-ray sources with the observed environment, so including a handheld GRS for targeted ground-based data collection can increase the value of the recorded data. KGS has successfully mapped variation of near-surface materials and confirmed the data as compatible with findings from the handheld spectrometer.