# UAV Detection and Tracking in Urban Environments Using Passive Sensors: A Survey
## 4 Anti-UAV System  
In recent years, there has been a significant amount of literature on anti-UAV systems, and several anti-UAV systems have been used commercially and militarily. One such system is DedroneTracker [113], a multi-sensor platform (RF, PTZ camera, radar) with countermeasure capabilities (jamming) released by Dedrone. The system can be extended and customized to meet specific field requirements and can automatically capture a portfolio of forensic data, including UAV make, model, time and length of UAV activity, and video verification. Dedrone also offers RF sensors and jammers, with a detection range of up to 1.5 km (up to 5 km in special cases) and a maximum jamming range of about 2 km. Droneshield [114] is another system that provides anti-UAV defense solutions, offering a range of standalone portable products as well as rapidly deployablefixed-site solutions. It employs a variety of surveillance technologies, including radar, audio, video, and radio frequency, to detect UAVs and provide effective countermeasures. Droneshield's jammer can immediately cease video transmission back to the UAS operator and allow the UAV to respond to a live vertical controlled landing or return to the operator controller or starting point. Another RF-based UAV detection system is ARDRONIS [115], developed by Rohde and Schwarz. ARDRONIS performs detection for frequency-spread spectrum (FHSS) signals and WLAN signals, with a detection range of up to 7 km for commercial off-the-shelf remote signals and up to 5 km for UAVs such as the DJI Phantom 4 under ideal conditions. The AUDS [116] system, on the other hand, uses radar technology, video, and thermal imaging to detect and track UAVs and has directional radio frequency inhibition capabilities. With its Air Security Radar, the range of detection can be up to 10 km. The ORELIA Drone-Detector system [117] consists of an acoustic sensor and software for protected object monitoring, target tracing, and sensor adjustment. The detection range is about 100 m, and multiple acoustic detectors can be installed to detect UAVs in all directions. Falcon Shield [118] is a rapidly deployable, scalable, and modular system that combines electro-optics, electronic surveillance, and radar sensors. ELTA Systems [119] is another solution that combines radar, RF, and photoelectric sensors to detect and track UAVs more than 5 km away and to take soft and hard kill measures against them. Each system uses different surveillance techniques and implements various functions, as summarized in Table 8. The examples of these systems are shown in Figure 3. These systems have demonstrated their effectiveness in UAV detection and tracking. To enhance their detection capabilities, the majority of anti-UAV systems opt to utilize multiple types of sensors. These systems primarily find application in scenarios such as airport operations and military protection. However, Dedrone stands out as a rare system provider that specifically addresses urban settings, including sports events and outdoor concerts. DeDrone and ARDRONIS are two anti-UAV systems that offer video evidence recording capabilities, although they employ different methods. DeDrone utilizes the visual monitor within the system to directly record video evidence when a UAV is detected. On the other hand, ARDRONIS obtains the UAV's field of view by intercepting the visual transmission signal of the UAV. It is important to note that while DeDrone can record and save evidence whenever a UAV is detected, ARDRONIS can only achieve video recording when it successfully cracks the visual transmission signal of the UAV. Dedrone's products and design concepts serve as a valuable source of inspiration for tackling the challenges of anti-UAV systems in urban environments. Their emphasis on scalable software platforms and leveraging existing infrastructure offers valuable insights for research and development in this field. By incorporating such approaches, it is possible to enhance the effectiveness and adaptability of anti-UAV systems in urban settings.