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Since their initial deployment during the First World War, drones have fast become an integral division of the aviation industry. Accelerated in recent years by the continuous reduction in size and weight of electronics, UAVs have proved their worth in areas such as aerial surveillance, disaster relief, and safety inspection. However, as their commercial availability increases, so does the threat of facilitated access to high-security locations and the accompanying anonymity of the pilot.
With incidents ranging from unintentional airport disruptions to the more meticulous implementation as a mode of drug smuggling, the development of systems capable of detecting drones has become a matter of national security.
The Challenge of Drone Detection
Drone detection may seem a manageable task when considering the long-established systems already in place for aircraft, yet this is not the case. A fundamental principle behind effective radar operation is that the dimension of the object is greater than the wavelength of the emitted radio signal. Hence, due to the smaller scale of drones, the current radar systems optimized for conventional aircraft are insufficient.
Furthermore, the similarity in size between drones and birds means the solution is not as simple as reducing the radio wavelength, but the capability to differentiate between aircraft and wildlife must also be designed. Additional complexity is introduced by the lower flight altitude of UAVs resulting in radar “clutter” as the signal is echoed from the ground, buildings, and other surrounding obstacles.
At present, the prevailing solution to such a challenge is the integration of multiple detection methods. Such an approach allows the multiple benefits of radar systems to continue to be exploited but with the limitations detailed above addressed through the coinciding employment of radio frequency, acoustic, infrared, and optical sensors. This article will cover the operation and advantages of optical detection systems.
Principals of Optical Detection Systems
An optical detection system refers to the recognition of an object via both the visible and infrared portions of the electromagnetic spectrum. In its most simple form, visible detection could refer to a soldier using binoculars to carry out surveillance from the ground or, as is the case for the integrated drone detection systems, the implementation of cameras.
Alongside this, the infrared spectrum is harnessed using infrared cameras to sense the radiation characteristic of an object’s temperature. For both visible and infrared cameras, the general operation consists of first measuring the radiation intensity before converting this into an electric signal to display the identified body on the chosen user interface.
These sensors are key to tackling platforms designed to have minimal radio frequency transmission, a common technique employed by stealth aircraft. As of yet, the ability to become optically invisible remains the stuff of fantasy.
It is during the initial object detection phase that infrared systems provide their greatest contribution. Their independence to adverse environmental conditions ensures constant operation day or night, unwavering in the face of rain or fog. As a result, any drone entering within the range of the camera will be automatically revealed by its heat signature on the thermal display.
An additional competitive advantage under investigation is the potential to determine the launch location of the drone. By recording the temperature of the vehicle’s monitor, the length of operation time may be deduced providing a key piece of data in the determination of the drone’s origin.
The use of visible light cameras becomes crucial in the identification of the detected target, especially for discrimination between vehicle and nature. As advances in optical technology continue to rocket, with the average detection precision increasing from 0.22 in 2013 to 0.8 in 2016, the cameras currently employed can zoom in to present high-resolution 3D images for object classification to be made.
The Spynel IR sensor offered by security system company HGH boasts 30x optical zoom capability. An additional direct consequence of such rapid progress in this field is the comparatively low cost of high-performance equipment as cutting-edge camera technology rapidly becomes commercially available, making them an economical solution.
Continuing Research
Despite the clear advantages provided by the employment of optical sensors, a perfect drone detection system is yet to be developed. As demonstrated last year with the 33-hour shut down of Gatwick airport, UAVs are still slipping through the clutches of air traffic control.
In direct response to this airport anarchy, defense technology company Raytheon has partnered with the counter-drone specialists Black Sage in the hope that the combined expertise could result in an answer to this crucial challenge.
Setting this collaboration apart from current systems is the provision of AI and radio-frequency jammers by Black Sage combined with Raytheon’s Windshear command and control system, resulting in the ability to, if necessary, take control of UAVs and land them safely. Only time will tell whether this promised solution soars above the others.
Sources and Further Reading
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