# State-of-the-Art Mobile Radiation Detection Systems for Different Scenarios
## 3 Mobile Platforms
### Air-Based Platforms
#### 3.3.2 Unmanned Aerial Vehicle  
UAVs major technological acceleration within the field has been evident since the incident at the FDNPP in March 2011 [17]. Despite the use of only two UAVs (against seven UGVs) during the emergency in FDNPP [11], this event marked the first use of a SUAS, the Honeywell T-Hawk [69; 70], a ducted fan UAV weighing 8 kg used for radiological surveys, structural damage assessment, and to foresee debris removal. The T-Hawk had a camera, a forward-looking infrared and a gamma dosimeter with time stamps readings and global positioning system (GPS) information. Even though this SUAS had autonomous vehicle and navigation capabilities its operation relied on the human-robot teaming. Since radiation intensity is inversely proportional to the square of distance and it is attenuated by the medium (air), it is important to consider SUAS due to their capability to fly at low altitudes and in close proximity to structures [69]. Missions where unmanned fixed-wing are superior compared to other unmanned platforms include radioactive plume tracking, sampling of airborne radioactive material, fallout mapping of large areas, and searching of unshielded sources, e.g., material out of regulatory control, both stationary and moving, from large areas. Despite the fact that rotatory wing has advantages, such as hovering and VTOL capacity, they have relatively shorter operating endurance/range and payload capabilities. Figure 3: Examples of underwater robots developed for inspection of nuclear reactors and other water-filled infrastructures: (**a**) Spherical underwater robot. ©2013 IEEE. Reprinted, with permission, from Reference [60]. (**b**) Underwater robot prototype [62], reprinted by permission of the publisher (Taylor & Francis Ltd, [[http://www.tandfonline.com](http://www.tandfonline.com)]([http://www.tandfonline.com](http://www.tandfonline.com))). VTOL aircrafts have several advantages as they can hover and need less space to launch and recover (do not need runway). They may include [71] multicopters/multi-rotors, such as quadcopters, hexacopters, or octocopters (e.g., quadcopter from Microdrones [72]), aerial robots (e.g., Honeywell T-Hawk [70]), single-rotor helicopter (e.g., Helicopter from UAVOS [73]), and fixed-wing hybrid VTOL, such as PD-1 from UKR SPEC systems (Figure 4a) [74]). Despite their great potential for radiation monitoring near surface, to the best of authors knowledge, no work has been done using hybrid VTOL fixed-wing (complex system) nor blimps or balloons platforms. Due to their hover capability and long endurance (none or low fuel consumption), blimps can be used for environmental monitoring and inspection applications. An example is the project autonomous unmanned remote monitoring robotic airship, which explored many aspects related to the dynamics, control, and guidance methods of an airship [75; 76]. A recently developed VTOL aircraft (2012) was the \"plummet-proof\" plane-blimp hybrid drone, also known as PLIMP (Figure 4b). To lift off, it uses both helium and rotational wings and, in the sky, can hover or maneuver better than a conventional blimp since it poses electric propellers for thrust and flight surfaces, like small wings [77]. In Table 2, a summary of the advantages and limitations of each air-based platform is provided. It is worth noting that, while manned vehicles require a human being, normally, be exposed to radiological risks (among others), the UGV/UUV/UAV can work in a fleet or a swarm of vehicles mitigating that risk for the operators. Figure 4: Examples of hybrid unmanned aerial vehicles (UAVs): (**a**) Hybrid vertical take-off and landing (VTOL) fixed-wing. Reproduced, with permission, from Reference [74]. (**b**) Hybrid plane-blimp (PLIMP). Reproduced, with permission, from Reference [77]. Copyrighted 2021 Plimp Airships, protected by national and international patent numbers D727242, D713320, 201815761, 005665221-0001, and ZL201830546681.0. \begin{table}
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