BACKGROUND

Aerial measurements and monitoring of radiological nature have been around for some time as has been demonstrated for instance by a joint comparison study of such systems between the US and Israel. However, until of recent, the focus has been in using large monitoring systems lifted by large aircraft such as helicopters flying at relatively high altitudes.

In recent years with the growing introduction of unmanned aerial vehicles (UAV), also sometimes referred as unmanned aerial systems (UAS), proposals of the usage of smaller detector units coupled with UAVs of various kinds including fixed wing systems, have started appearing, albeit in principle UAVs of all sizes may be used.

The growing interest in, and research and utilization of small autonomous multi-rotor UAVs (mostly quadcopters) for disaster scenarios and for routine inspection and monitoring has been particularly booming in recent years. Around the same time, the occurrence of the Fukushima nuclear accident has contributed to development of UAVs specific for radiation monitoring and mapping. Such usage of multi-rotor UAVs has the advantage of being able to fly at lower altitudes than fixed wing UAVs and at lower speeds, demonstrating that a good resolution for ground contamination can be achieved despite the usage of small detectors. It was also recognized that UAVs are advantageous over manned vehicles (both ground and aerial) in rough terrain and in minimizing radiation exposure to personnel.

Another recent development has been the usage of multiple UAVs in communication with each other, i.e. in swarms that can be utilized for mapping of radiation fields in 3D, which may be of significant advantage in a scenario of a prolonged plume-type release of radionuclides.

CONSIDERATIONS

From the survey of literature some distinct advantages for the usage of UAVs can be identified. First, the cost of such small systems, in light of commercialization in recent years, is negligible compared with traditional piloted aircraft. Immediately following is the ease of launching and operation of UAVs which are mostly automated and do not require extensive pilot training. In this regard the first advantage of multi-rotor over fixed winged systems becomes clear, owing to their much greater ease of deployment, maneuvering and hovering-in-place capabilities. A second advantage of copters over fixed-wing planes is their ability to fly at lower speeds and altitudes (a fixed wing plane must maintain a relatively high velocity), allowing for high resolution mapping with small detectors. On the other hand with the higher velocities and energy efficiency achievable by fixed-winged aircraft, it is possible to air sample at much higher rates and volumes compared with multi-rotor copters. Given the above advantages and the wide-spread and growing commercial availability of copter systems, it was concluded the work conducted that in most scenarios a multi-rotor UAV system is preferable over a fixed-wing system.

The use of such UAVs is versatile and a single system can assist in various measurements that would previously require several types of air and ground based systems. These include measuring of ground contamination concentration, plume 3D distribution, gamma spectrometry, and volumetric air sampling for radionuclide concentration.

IDENTIFIED REQUIREMENTS

The literature survey identified and suggested the following equipment for carrying aboard an UAV equipped for a radiological mission: Hi-Res Camera, Thermal Camera, Compton camera, Spectral detector, High gamma field detector (Geiger), Air sampling filter and volume monitor. Suggested autonomous navigation capabilities that were identified are: Scanning, Obstacle avoidance, Contour following, Environment-aware return to home, Return to highest reading. Another automatic requirement identified was the ability to operate multiple UAV systems simultaneously as a swarm although the exact nature of a multi-UAV mission has yet been characterized.