The effective mitigation of all threats posed by either careless or malevolent UAS operations begins with the ability to detect the presence of a drone within the three-dimensional perimeter surrounding critical infrastructure or events.
Passive C-UAS measures employing radar, RF, or EO/IR sensing technologies can enhance physical overwatch to detect and track threatening UASs overhead. But these technologies are not without limitations.
Small drones like the DJI Phantom drone flown at lower altitudes at speeds close to 100 mph can be hard to detect by radar and other detection sensing technologies. Likewise, passive C-UAS technologies can be optimal when operated within a clear skyline and uncluttered background. Still, they become less effective if an operator of a threatening drone is navigating in overcast, cloudy airspace, or among tall trees and other environmental barriers. The physical landscape can provide cover and concealment for a threatening drone, impeding the direct line of sight necessary for successful drone detection.
For example, if a threatening drone passes behind a tall building or a swarm of small drones is among other airborne objects like birds, passive C-UAS technologies may lose their ability to detect and track the drones be unable to distinguish the drones from other airborne debris accurately.
Furthermore, technologies analyzing acoustics within the environment to detect unauthorized drones may have limitations due to the quantity and quality of microphones onboard and their tolerance of ambient noises. Perhaps, a prevailing limitation of acoustic C-UAS systems is their limited internal library of sounds emitted only by commonly used drones of today.
Although active C-UAS technology is intended to interdict and disrupt UAS communications links, they too have proven ineffective in specific environments, such as busy airspace, where the officials need to be mindful that the jamming technology is not pointed at or near other authorized aircraft and does not affect other RF and GPS signals. Besides, it is challenging in airports to account for multiple variables, such as speed, travel direction, and the altitude of the target drone.
Even with their impressive history, the effectiveness of laser weapons systems is also limited by the complexity of technology and environmental factors, such as weather, smoke, and other airborne debris.
Regarding kinetic C-UAS measures, using technology, such as a net gun to intercept a drone or to arm an interceptor drone with a net gun to chase and capture a drone, seems to be gaining popularity. However, studies show that the effectiveness of kinetic measures is dependent on the competency of the C-UAS operator because today’s drones are capable of reaching speeds over 100 miles per hour.
Unintended consequences of C-UAS
Although C-UAS technologies seem to be the only current countermeasure authorized for state and local law enforcement, they are not absolute and have drawbacks. Therefore, before implementing C-UAS, public safety entities should assess the potential consequences when deployed within their urban communities.
According to studies, all C-UAS detection systems can generate both false negatives and positives, and these false alarms can have negative consequences. False reports from EO/IR detection technology that senses a bird rather than a drone may be a nuisance. At the same time, radar systems with reduced sensitivity can result in missing the detection of small UAS threats. Either of these consequences, over time, could reduce overall confidence in the technology’s accuracy.
To be effective, the noise emitting from an RF jammer are at a power level high enough to cover up the radio communication signal between the drone and the pilot. This countermeasure can cause collateral damage to authorized users of the same airspace by unintentionally interrupting their communications systems. Unintentionally jamming communications signals of other RF-enabled systems can be hazardous.
Manned aircraft may not be the only thing affected by active C-UAS technologies, such as spoofing or jamming signals. Instances have occurred in which the disruption of radio wave communications has not only caused the loss of autopilot systems of manned aircraft but has also caused doors of commercial businesses to randomly open and close.
An overarching consequence of kinetic means to counter a threatening drone is the possibility of causing a drone to fall to the ground, damaging other property, or worse, further endangering the public’s safety in crowded urban areas.
The below table will summarize the limitations and unintended consequences of C-UAS technologies.
| C-UAS technologies | Limitations |
| Radar | Smaller drones may be hard to detect. |
| Radio-frequency (RF), Electro-Optical (EO)/Infrared (IR) and Acoustic | Cloudy, overcast skylines, and the existence of other airborne debris or birds may decrease the effectiveness of RF, EO/IR, and acoustic technologies. Generation of false negatives and false positives, creating low confidence in the technologies capabilities that results in complacency and the potential to miss credible UAS threats. |
| RF and GNSS Jamming | Environmental factors, such as crowded airspace, make deployment of jamming technologies complicated because of multiple variables, such as speed, the direction of travel, and altitude of the target drone, and the existence of authorized aircraft in the area vulnerable to signal jamming. Collateral damages, such as interference with authorized manned aircraft and their navigational aids or radio waves, supported security measures taken by businesses and individuals within an urban environment. |
| Spoofing | UASs with inertial navigation systems can be immune to spoofing technologies since GPS signals are unnecessary for successful navigation. |
| Laser | Can be limited due to environmental factors, such as weather and smoke in the atmosphere. Because of a limited interaction time to engage a threatening drone, the operator of C-UAS laser technology must be well trained to achieve an accurate beam deployment. |
| Netting | Limited range of approximately 49 feet. With drone speeds reaching over 100 mph, interceptor drones may not actually catch threatening drones. The complete destruction of or loss of control of UAS platforms can cause a drone to fall from the sky, endangering life and property on the ground. |
