Package delivery, media work, entertainment and recreation, drones are known for their seemingly innocent applications. Often overlooked by the general public, is their potential usage for criminal, malicious or terrorist activities which due to the effectiveness and efficiency of drones, is also very convenient.
To address the issue, drones are banned in some areas around the world and are shot down at certain proximities to certain buildings. But just detecting a drone in an area flying at a high altitude, let alone shooting it down, is easier said than done. Most conventional radars are incapable of detecting objects as small as a drone, not only that, the maneuverability and the ability to blend in and avoid detection by radar is very easy for a drone that is small in size.
The research letter titled, ‘Consumer Drones Targeting By SODAR (Acoustic Radar)‘, attempts to innovate the radar system so as to make it an efficient tool of detecting objects like consumer drones and small unmanned aerial vehicles (UAV).
As the researchers studied different means of detection like the usage of cameras to even detect drones and UAVs camouflaged as birds, they argue that very fine and accurate detection is not feasible. On top of that, cameras can only detect drones or flying objects over a small distance. Outside of that range, a detection system based on cameras is not accurate enough for effective application. Thus, the researchers decided that developing a radar system based on acoustics would be the most effective means to detecting drones and UAVs.
In this letter, the researchers demonstrated through a field experiment how a well-assessed active acoustic remote sensing technique, widely used in atmospheric studies, can be tuned and adapted to both detect as well as track UAVs.
The detection and tracking device deployed in the research experiments was a custom-made mini-SoDAR (Sonic Detection And Ranging), an instrument widely used in a number of atmospheric applications spanning from wind and turbulence profiling to surface and boundary layer studies.
They did not just theorize, hypothesize or propose the usage of sonar for drone detection and tracking, they did practical experiments to observe the shortcomings in the model developed for Acoustic Sodar radar. The UAV to be detected was allowed to take off from a distance of 50 m from the mini-sodar antenna, and flew inside its FOV cone for approximately 9 min, a time long enough to perform a convincing statistical analysis. During this period, the UAV reached a maximum distance of about 146 m from the antenna. The location of the UAV detected and tracked by the sodar system in a certain time interval was compared with the actual, standard location of the UAV continuously reported by the GPS module installed in the drone. The considerable agreement between the two different readings practically confirms and verifies the proposed idea of an Acoustic radar as well as its feasibility of application.
To ensure the Acoustic Radar’s performance during the heavy noise of the rotors of the drone or any aircraft or even residual noise is very important. The feat was achieved by preventing saturation of signals due to the loud noise caused by the UAV rotors, the analog signal from the antenna was amplified as little as possible
In their letter, they demonstrated how a the acoustic technique commonly and almost exclusively utilized in atmospheric physics could be utilized for not only detecting but also tracking drones in real time, continuously. The height of the UAV reported by the mini-sodar profiles matched the onboard GPS between 60 and 150 m from the ground, which can be considered as highly accurate, with an error almost equal to unity and no significant bias.
This study in radar technology, or to be more precise, in acoustic radar systems, stirs encouragement in further experiments based on the said technique, as in principle a tri-axial system would be capable of tracking UAVs speed and 3-D position with acceptable accuracy. Despite that, the comparatively low velocity of sound in the air represents a limitation that cannot be overcome, since the instrument temporal resolution is closely related to the maximum detectable range.
It has to be acknowledged and noticed that besides detecting unidentified aircrafts in any designated vicinity, working on drone detection and tracking could also contribute to improve the discrimination between atmospheric and non-atmospheric targets in the programmed algorithms as the drones process the data they capture.
Citation: Casasanta, Giampietro & Petenko, Igor & Mastrantonio, G & Bucci, Simone & Conidi, Alessandro & M. Di Lellis, Andrea & Sfoglietti, Giulio & Stefania, Argentini. (2018). “Consumer Drones Targeting by Sodar (Acoustic Radar)”. IEEE Geoscience and Remote Sensing Letters. PP. 1-3. 10.1109/LGRS.2018.2858930. https://ieeexplore.ieee.org/document/8430530/