## 4 Avinomics Assessment
### RGB-D Cameras
#### Position sensors  
UAV movements are detected via position sensors, where the latter provide spatial information with respect to a defined reference. Such sensors are generally used in UAVs to pinpoint their precise location in order to later share it with the user/control operator (for cases of semi-autonomous and human-controlled UAVs) or to compute it in the navigation control (for cases of autonomous UAVs). Therefore, position sensors determine the orientation of a UAV in addition to providing odometric information about it [276]. In this paper, position sensors are mainly classified according to their purpose of usage/outcome, characterized as either tracking/localization or proximity/ radar. 1. Tracking/localization The localization-based navigation strategy as well as the target tracking scheme under the control section obtain their inputs from sensors such as GPS, IMU, and Ultra-Wide Band (UWB) [277]. On one hand, GPS sensors provide accurate time-space information for UAVs. Specifically, the Real-Time Kinematic (RTK) GPS technique provides positioning updates with high frequency and is thus able to withstand a UAV's swift velocities and high maneuverability [278]. For instance, a high-precision RTK GPS was used in [279] for the purpose of determining the locations of a ground control target. In addition to  
Figure 8: Sample thermography data obtained from a UAV-embedded thermal camera [275]. localization, GPS modules embedded in UAVs provide temporal information, which can also be used for stabilization. The u-blox NEO-M8N [280] representing a low-power compact form GPS receiver, was used in [281] to solve the problem of wind gusts with their adverse effects on UAV steering while inspecting transmission lines. On the other hand, IMUs are most probably found in UAVs in the form of accelerometers, gyroscopes, and magnetometers [282]. Along with GPS modules, IMUs form INS, which is responsible for localizing, stabilizing, and tracking a UAV. In the work [283], with its UAV shown in Figure 9, the corresponding IMU (i.e., GPS antenna, magnetometer) had the function of attitude determination, localization, and navigation of a UAV. In addition to the GPS and IMU modules, UWB sensors utilize pulses of short-range radio frequency to determine the location of nearby objects. The location of a target is known when the UWB receiver receives (according to a specific frequency spectrum) the corresponding pulses sent by the UWB transmitter [284]. For positioning, UWB utilizes either the time difference of arrival approach [285] or the two-way ranging method [286]. DWM1000 [287] is a commonly used UWB transceiver module, supporting four radio frequencies from 3.5 GHz to 6.5 GHz, with a data rate up to 6.8 Mbps. In the work [288], the DWM1000 orchestrated ranging measurements between a UAV and fixed anchor nodes, eventually localizing the UAV precisely. This suggests how UWB can help in positioning UAVs in GPS-challenging environments. (b) Proximity/radar  
In short, proximity sensors provide spatial information with respect to objects existing nearby in their field (i.e., detecting objects in short ranges via IR and other ultrasonic technologies). Radar sensors, on the other hand, use radio waves to detect objects located at greater distances than those in the previous case. Concerning ultrasonic proximity sensors, HC-SR04 [289] provides from 2 cm to 400 cm of non-contact distance measurements with an accuracy of \(\pm 3\) mm. Such a sensor was used in reference [290] to detect nearby objects of an indoor UAV. As an alternative, MaxSonar MB1222 [291], with a higher range in object-detection than the previously mentioned sensor (i.e., 20 cm to 765 cm), finds application in indoor localization of micro-UAV, with accurate performance [292]. From a different perspective, mmWave radar sensors provide accurate target range and velocity information, surpassing the other alternatives under extreme weather conditions [293].