Drone detection in urban environments
Low-flying drones are hard to spot with the human eye as well as when using technical equipment. It is even harder to detect them when they are flying in urban areas where visibility is restricted. For this reason, armasuisse S+T investigated new ways of detecting drones in the Armed Forces training village in Bure. As part of these efforts, state-of-the-art detectors were installed around the village on rooftops, vehicles and the ground.
09.09.2020 | Research Management and Operations Research, Dr. Peter Wellig
Up until recently, drones were often reserved for use by the military. Small drones have since been able to be purchased at cheap prices from specialist retailers and are being used and misused more by civilians. For example, criminals and terrorists have in the past used small commercially available and also homemade drones for illegal purposes. One well-known event was the blockade of Gatwick Airport in London, where multiple drones were flown illegally in the airport’s airspace for 32 hours. This meant that all aircrafts coming into or leaving the airport were at risk of not being able to take off or land safely. There have been other instances in which drones were used for terrorist attacks during the conflicts in Iraq and Syria, targeting people and infrastructure.
As a result, companies are supplying system solutions for the earliest possible detection of drone risks. These systems can be used to detect low-flying drones from long distances. However, how can drones be successfully detected in urban areas with restricted visibility?
In order to examine new ways of detecting drones in urban areas, armasuisse Science and Technology carried out a field test as part of a research experiment at the Bure military training area in the canton of Jura from 24 to 28 August 2020. During this test, the Nalé Armed Forces training village simulated a situation with urban conditions and restricted visibility in which various detectors such as radar equipment, microphones and cameras were set up to detect drones. The modern detectors used encompassed both commercial systems and experimental systems that are not yet available to purchase commercially.
Microphones and cameras showed promise for being used in urban environments
In order to be able to detect the noises made by drones, even if the drones are, for example, hovering behind a wall, microphones were distributed uniformly around the training village and also installed on a car. Microphones were not the only equipment to show promise in detecting drones in urban areas, as the camera systems used and tested also delivered successful results. For example, a drone equipped with cameras hovered 80 metres over the Armed Forces training village, monitoring the situation and keeping an eye out for any drones flying above the rooftops. The surveillance drone was connected to the ground via a power and data cable and was thus able to monitor the village for hours without having to have its batteries changed. Also of interest was the use of a special camera – the event camera, which can detect quick changes, such as approaching drones. Furthermore, the cameras, which can record images in various spectral ranges, showed that they can work with the systems in complementary fashion. This means that in the future, the contrast between the background and an approaching drone can be increased by fusing the images recorded by different cameras, which would enable drones to be easily detected in urban environments.
The use of innovative transmit-receive geometries for radar equipment
Radar equipment can also be used to detect drones. To this end, new methods were examined in Bure. For example, a multistatic radar network comprising a transmitter and two receiver units used an innovative transmit-receive geometry for detecting drones. In addition to this, a cognitive radar network with four small radar devices was used to monitor the labyrinth of streets and roads within the village. The detection capabilities of a passive radar system were also tested. In this respect, passive means that the radar system did not transmit radar waves itself, but did receive signals from radio transmitters. The signals received had been reflected by drones and should therefore be detected, but only further analysis will show whether this was the case.
After the field test, armasuisse S+T and its research partner will analyse the measurement data recorded and draw up the results. The recommendations derived from these results should illustrate which technologies are better suited for future drone detection than others and which developments should be monitored further.
Various cameras and microphones were distributed around the Armed Forces training village.
The colour of a drone also contributes to the ease at which they are detected, which is why drones of various colours were considered.
On the right in the foreground the visual camera can be seen. In the background, the drone is flying just beyond the forest perimeter and towards the village.