FOR SOMETHING weighing only a few kilograms and costing less than $2,000, even for a sophisticated model, a small consumer drone can cause an awful lot of havoc. On January 22nd flights in and out of Newark airport, near New York, were suspended temporarily after reports of a drone being aloft nearby. On January 8th Heathrow, London’s biggest airport, also shut briefly because of a drone sighting. And in the busy run-up to Christmas London’s second airport, Gatwick, was closed for more than 36 hours after drones were spotted flying near its runway. EasyJet, the biggest operator at Gatwick, said this week that the grounding of flights had cost it £15m ($19.3m).
Airport incursions are not the only danger posed by drones. A growing number of close encounters with drones are being reported by airline pilots. On December 12th a Boeing 737 belonging to Aeromexico managed to land safely at Tijuana after its nose was badly damaged in a collision with what may have been a drone. Elsewhere, drones are being used to smuggle goods across borders, drugs into prisons, to attack military bases with explosives and in assassination attempts, like that which took place last August on Nicolás Maduro, the president of Venezuela.
The authorities are increasingly concerned. Christopher Wray, the director of America’s Federal Bureau of Investigation, said recently that the threat to his country from attacks by rogue drones “is steadily escalating”. There are no easy answers to the problem, although it helps to define the nature of the threat. Irresponsible drone pilots might be kept in check by better education, tough penalties and more manufacturers installing features such as “geofencing” in drones’ mapping software, to prevent them straying into restricted areas. But terrorists and their like will not take any notice of rules and regulations, and they will hack software restrictions or build their own drones from readily available components to try to defeat countermeasures. To combat rogue drones will therefore require better technology.
The most extensive review of counter-drone products, by Arthur Holland Michel, co-director of the Centre for the Study of the Drone at Bard College, New York, and his colleagues, is now a year old, having been published in February 2018. Even then, though, at least 235 such devices and systems were on sale or in active development. The most popular methods of drone detection were radar, locating the radio frequencies used by drones, and watching out for them with cameras. But other approaches, including infrared sensors and acoustic devices that can recognise the sounds produced by a drone’s electric motors, were also employed. The most frequently used countermeasure was radio-jamming. Because of a lack of industry standards, the report concluded, there was wide variation in the effectiveness and reliability of the technology.
Some anti-drone systems are based on military hardware, and may be more suitable for use on a battlefield than in civvy street. Firing missiles, bullets or high-energy lasers to bring down a drone in the vicinity of a commercial airport is dangerous. Besides the risk of hitting unintended objects, or even people (a rifle bullet can still be travelling at lethal velocity several kilometres from where it was fired), there is also the possibility that a target drone may not be knocked out completely, and may thus spin out of control to crash somewhere that causes serious damage or injury. Nor are small drones easy to hit. One that was flown into Israeli airspace from Syria in 2016 survived two attacks using Patriot missiles, as well as rockets fired from a fighter jet.
Countermeasure for measure
Airport operators also need to be careful about electronic countermeasures, warns Iain Gray, director of aerospace at Cranfield University, in Britain. Signal-jamming can block the link between a drone and its operator, or overwhelm a GPS-based navigation system. But unless such jamming is carried out carefully it might also damage an airport’s sensitive radio and navigation equipment, and the instruments on aircraft, says Dr Gray. If every plane at an airport had to be checked to ensure it was safe to fly after electronic countermeasures were deployed, that would cause extensive delays in resuming operations.
Anti-drone technology is, nevertheless, improving. This week Indra, a big Spanish technology company, said it had completed extensive testing in “dangerous” places of an anti-drone system called ARMS. Once the system’s sensitive radar has picked up a drone, ARMS uses infrared cameras to confirm and identify the type of drone. Electronic-warfare sensors then sweep the radio spectrum to determine what signals the drone is using. This permits ARMS to attempt a “soft kill”—a carefully targeted form of jamming. Indra claims that the system is precise enough to disable either a single drone or a swarm of them, by modulating the level of response, without affecting other electronic equipment on an airfield. Like other approaches, it can also use various “spoofing” techniques, which involve generating bogus signals that can be used to try to seize control of a drone.
Such counter-drone systems can be made portable, permitting them to be used at special events. And they will become increasingly sophisticated. QinetiQ, a British defence firm that makes a counter-drone system called Obsidian, has found ways to use signals to disrupt the electronic circuits within a drone, allowing it to disable a drone’s camera or turn off its electric motors. Obsidian can also analyse a drone’s flight characteristics and the loading of its electric motors. That helps determine how heavily laden the drone is, and thus whether it might be carrying explosives.
Both Indra and QinetiQ use an advanced form of radar that operates in three dimensions. Such 3D radars will be particularly valuable at airports, says Dr Gray. Existing airport radars are bad at picking up small things like drones. Even if they do spot them, they struggle to distinguish them from birds. Conventional 2D radar scans an area using a narrow rotating beam and detects objects when the signal is bounced back, providing range and direction. Height can be determined by a second radar. A 3D radar combines all three measurements, sometimes by using a fixed array that floods an area continuously with a signal. The returning signals are processed to create a three-dimensional model of the entire airspace surrounding an airport.
One firm making an anti-drone system that uses 3D radar is Aveillant, based in Cambridge, Britain. Aveillant says Gamekeeper, as it dubs its equipment, can detect and classify a small drone up to 5km away. As drones can be difficult to spot by eye, even when they are only a few hundred metres away, 3D radars of this sort would allow airports to detect drone incursions more quickly and be more confident about when it is safe to resume flights.
There are plenty of other ideas for dealing with drones. These include launching defence drones to capture villainous craft by entrapping them in a net; hand-held bazooka-like guns that fire nets propelled by a blast of compressed air; and portable radio-jamming equipment, similarly shoulder-mounted and hand-aimed. In the Netherlands, the police have even tried using trained eagles to attack and bring down small drones, although the idea was eventually dropped. All these methods, though, share a flaw. They usually require operators to be at hand and fairly close to an intruding drone.
That is also true of what might seem the most obvious and simplest way to deal with a drone: a shotgun. Some folk nevertheless think this could be worth a go. Snake River Shooting Products, a firm in Idaho, sells cartridges it says are specially designed to knock a small drone out of the sky. But as the firm scrupulously reminds its customers, they need to use their common sense and obey all laws. One of which is that in America a drone is considered to be an aircraft, and people are not, as a rule, supposed to shoot at aircraft.