  Natural Resources Canada (NRCan) is responsible for the provision of aerial
radiometric surveys in the event of a radiological or nuclear emergency in
Canada. Manned aerial surveys are an essential element of the planned
consequence management operation, as demonstrated by the recovery work
following the 2011 Tohoku earthquake and tsunami, and their effects in
Fukushima, Japan. Flying lower and slower than manned aircraft, an unmanned
aerial vehicle (UAV) can provide improved spatial resolution. In particular,
hot spot activity can be underestimated in manned survey results as the higher
flight altitude and wider line spacing effectively average the hot spot over a
larger area. Moreover, a UAV can enter an area which is hazardous for humans.
NRCan has been investigating the inclusion of UAV-borne radiation survey
spectrometers into its aerial survey response procedures. The Advanced
Radiation Detector for UAV Operations (ARDUO) was developed to exploit the
flight and lift capabilities available in the under 25kg class of UAVs. The
detector features eight 2.8cm x 2.8cm x 5.6cm CsI(Tl) crystals in a
self-shielding configuration, read out with silicon photomultipliers and
digitized using miniaturized custom electronics. The ARDUO is flown on a main-
and tail-rotor UAV called Responder which has a 6kg lift capacity and up to
40min. endurance. The performance of the ARDUO-Responder UAV system was
characterized in both lab and outdoor trials. Outdoor trials consisted of
aerial surveys over sealed point sources and over a distributed source. Results
show how the directional response of the ARDUO can provide an indication in
real time of source location for in-flight guidance. As well, the results show
how use of the directional information in post-acquisition processing can
result in improved spatial resolution of radiation features for both point and
distributed sources.
