FIELD TESTS OF A UAV-COMPATIBLE SPECTROMETER TO EVALUATE ITS SUITABILITY FOR DETAILED SOIL RADON POTENTIAL MAPPING

As part of our ongoing research on radionuclide mapping and radon hazard characterization, we performed field tests to evaluate the suitability and limitations of a sUAV-compatible gamma spectrometer. To date, we have completed stationary data collection, mobile ground collection, and multi-level sUAV flights over a known material transition, as well as redundant ground and multi-level UAV data collection over a relatively uniform area. We chose to use total counts as a measure of soil radionuclide levels for our data collected above background because, although our test sites were in regions underlain by bedrock with high indoor radon levels, uranium counts were barely above background levels. The spectrometer can delineate obvious surface material contrasts (e.g., grass versus asphalt or concrete) analogous to boundaries such as faults juxtaposing different rock units. As the height of the instrument increases above a single surface type, the sensitivity of the spectrometer decreases linearly above the ground while the on-ground footprint increases geometrically. This limits the ability to resolve geologic boundaries. In areas covered by distinctly different surface types, the variation in counts is a function of both altitude and the proportion of each surface type within the footprint of the spectrometer at that location and height. In some cases, height appears to contribute to an increase in counts if the instrument is over a low-count surface material, but the complete spectrometer footprint is dominated by a high-count surface material. Our ongoing research will quantify background variability to help identify local variations in a low signal-to-noise (low gamma) environment, including the feasibility of stacking results from multiple single-height flights or profiles to cancel noise and amplify changes across geologic boundaries. Results from multi-level flights will also contribute to our understanding of instrument sensitivity and spatial resolution as functions of flying height. This publication was made possible by Grant P30 ES026529 from the National Institute of Environmental Health Sciences. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIEHS.