# UAV Detection and Tracking in Urban Environments Using Passive Sensors: A Survey
## 4 Anti-UAV System
\begin{table}
\begin{tabular}{l c c c c c c c c c} \hline \hline \multirow{2}{*}{**System**} & \multicolumn{3}{c}{**Technology**} & \multicolumn{3}{c}{**Function**} & \multicolumn{3}{c}{**Video**} \\  & **Radar** & **Audio** & **Visual** & **RF** & **Detection** & **Tracking** & **Defense** & **Recording** & \\ \hline DedroneTracker & ✔ & ✘ & ✔ & ✔ & ✔ & ✔ & ✔ & ✔ & 5000 m \\ Droneshield & ✔ & ✔ & ✔ & ✔ & ✔ & ✔ & ✔ & ✘ & - \\ ARDRONIS & ✘ & ✘ & ✔ & ✔ & ✔ & ✔ & ✔ & ✔ & 5000 m \\ AUDS & ✔ & ✘ & ✔ & ✘ & ✔ & ✔ & ✔ & ✘ & 10,000 m \\ ORELIA & ✔ & ✘ & ✘ & ✔ & ✔ & ✘ & ✘ & 100 m \\ Falcon Shield & ✔ & ✘ & ✔ & ✔ & ✔ & ✔ & ✘ & - \\ ELTA & ✔ & ✘ & ✔ & ✔ & ✔ & ✔ & ✘ & - \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Comparison of anti-UAV systems. Based on our observation, the more mature anti-UAV systems are currently mainly focused on military applications, and these systems are often implemented using a combination of multiple sensors. RF monitoring, radar, and vision sensors are the three most commonly used types of multi-sensors. However, radar is not suitable for use in certain locations, such as urban environments, due to its strong radiation characteristics [22]. In urban environments, RF surveillance emerges as a crucial method for locating UAV pilots, while visual surveillance plays a pivotal role in capturing UAV flight videos as evidence of intrusions. This combination of RF and visual surveillance techniques provides a highly competitive solution for UAV detection in urban settings. Although the acoustic-based method has shortcomings such as small detection range and being easily affected by noise, it can also provide an effective supplement for UAV detection under certain conditions, such as poor visual conditions and complex electromagnetic environments. Inspired by the above anti-UAV systems, we propose several suggestions for developing effective and scalable general anti-UAV systems. First, it is essential to consider the specific needs and requirements of the application scenario when selecting and combining sensors. Indeed, various environmental factors can impact the effectiveness of different surveillance methods in urban environments. For instance, visual surveillance may face challenges in locations with low visibility caused by heavy fog, sand, or dust. Similarly, complex electromagnetic environments can negatively affect the performance of RF surveillance. Additionally, acoustic surveillance may not be suitable in areas with strong winds or high levels of ambient noise. It is essential to consider these factors when selecting the most appropriate surveillance method for UAV detection, ensuring optimal performance in diverse urban scenarios. Second, the detection and tracking components of the system should be integrated with appropriate countermeasure capabilities. One of the most prevalent countermeasure equipment against intruding UAVs is the use of RF jamming guns. These devices are designed to disrupt the communication and control signals of the UAVs, forcing them to either land or return to their point of origin. RF jamming guns are widely employed as a common UAV countermeasure. Another commonly utilized countermeasure involves deploying UAVs to capture intruding UAVs. This approach involves using specially designed UAVs equipped with nets, cables, or other mechanisms to physically intercept and capture the unauthorized UAVs. Both RF jamming guns and UAV capture methods serve as effective countermeasures in mitigating the risks and potential threats posed by unauthorized UAV activities. Figure 3: Examples of anti-UAV systems: (**a**) DeDrone, (**b**) Droneshield, (**c**) ARDRONIS, (**d**) AUDS, (**e**) ORELIA, (**f**) Falcon Shield, (**g**) ELTA. The aforementioned images are sourced from multiple official websites of anti-UAV systems. Third, the system should be designed to be scalable and modular, allowing for easy deployment and adaptation to changing conditions. The design concept put forth by Dedrone Company offers valuable inspiration.