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Radiation mapping using a double exponential attenuation model for UAV sensing in forest area

Changing amount of radiation dose has been a great concern by citizen near the difficult-to-return area after the Fukushima Daiichi nuclear disaster. Rigorous assessment of public safety including inaccessible forest areas at a meter level is one of the keys in the disaster recovery plan. Each measurement point near the ground surface in UAV (Unmanned Aerial Vehicle) sensing are exposed from the effects of radiation emission from various angles in the fields including forest and plain, and thus acquisition of the attenuation characteristics on site is not realistic by simply using the spatial integration of point-kernels. The proposed method in this paper utilizes a double exponential curve for the least-squares fitting. The field test at a resident in the forests near the difficult-to-return area was performed, and we found not only a strong correlation between measured value and estimation result of the proposed method (r = 0.86, p < 0.01) but also the improvement of more than 10% in RMSE (root mean squared error) from results of the existing methods using an exponential decay function. Importantly, the experimental result suggested that the proposed method completely accepts to use the different measurement data, both measurement points near the ground surface and the flight heights during the UAV sensing.