Ask Hackaday: How Would You Detect A Marauding Drone?

The last few days have seen drone stories in the news, as London’s Gatwick airport remained closed for a couple of days amid a spate of drone reports. The police remained baffled, arrested a couple who turned out to be blameless, and finally admitted that there was a possibility the drone could not have existed at all. It emerged that a problem with the investigation lay in there being no means to detect a drone beyond the eyesight of people on the ground, and as we have explored in these pages already, eyewitness reports are not always trustworthy.

Not much use against a small and mostly plastic multirotor. Sixflashphoto [CC BY-SA 4.0]
Not much use against a small and mostly plastic multirotor. Sixflashphoto [CC BY-SA 4.0]

Radar Can’t See Them

It seems odd at first sight, that a 21st century airport lacks the ability to spot a drone in the air above it, but a few calls to friends of Hackaday in the business made it clear that drones are extremely difficult to spot using the radar systems on a typical airport. A system designed to track huge metal airliners at significant altitude is not suitable for watching tiny mostly-plastic machines viewed side-on at the low altitudes. We’re told at best an intermittent trace appears, but for the majority of drones there is simply no trace on a radar screen.

We’re sure that some large players in the world of defence radar are queueing up to offer multi-million-dollar systems to airports worldwide, panicked into big spending by the Gatwick story, but idle hackerspace chat on the matter makes us ask the question: Just how difficult would it be to detect a drone in flight over an airport? A quick Google search reveals multiple products purporting to be drone detectors, but wouldn’t airports such as Gatwick already be using them if they were any good? The Hackaday readership never fail to impress us with their ingenuity, so how would you do it?

Can You Hear What You Can’t See?

It’s easy to pose that question as a Hackaday scribe, so to get the ball rolling here’s my first thought on how I’d do it. I always hear a multirotor and look up to see it, so I’d take the approach of listening for the distinctive sound of multirotor propellers. Could the auditory signature of high-RPM brushless motors be detected amidst the roar of sound near airports?

I’m imagining a network of Rasberry Pi boards each with a microphone attached, doing some real-time audio spectrum analysis to spot the likely frequency signature of the drone. Of course it’s easy to just say that as a hardware person with a background in the publishing business, so would a software specialist take that tack too? Or would you go for a radar approach, or perhaps even an infra-red one? Could you sense the heat signature of a multirotor, as their parts become quite hot in flight?

Whatever you think might work as a drone detection system, give it a spin in the comments. We’d suggest that people have the confidence to build something, and maybe even enter it in the Hackaday Prize when the time comes around. Come on, what have you got to lose!

Ooops, Did We Just Close An Airport Over A UFO Sighting?

Picture this: it’s late in the evening on a freezing cold, dark, and windy December night in southern England, and an airport worker at Gatwick — London’s second international airport — sees something fly past in the gloom above the floodlights. The weather and darkness makes it difficult to see what the object was, but the report is phoned in to security. What was it? A flock of birds? A piece of plastic litter caught by the wind and blown through the night? In this case, the call is recorded as a drone. Because the magic D-word has been uttered, a security plan swings into action, the airport is put on a high state of readiness, and flights are suspended.

Gatwick by night, on an evening far less inclement than last week. News Oresund [CC BY 2.0].
Gatwick by night, on an evening far less inclement than last week. News Oresund [CC BY 2.0].
Thousands of people across the site are put on alert, watching for the drone. And of course, the drone reports roll in, and the story takes on a life of its own. People who have no idea what a drone looks like in the air are now expecting to see one, so of course when a flock of birds or a plastic bag caught by the wind crosses their peripheral vision they too are convinced that it is the drone. Night turns into day, there is a lull in the reports so the airport re-opens, only to be closed again following a fresh spate of sightings. Flights are diverted all across the country, and tens of thousands of passengers are stranded in the terminals.

No, it's not a speck of dirt on your screen, it's a drone! BBC (Fair use)
No, it’s not a speck of dirt on your screen, it’s a drone! BBC (Fair use)

There follows three days of airport closure drama. No photos emerge despite almost every one of the many thousands of people on the site having a camera phone from which they are Tweeting about the queues in the terminal. There is a grainy video, but it is indistinct, and crucially it doesn’t have anything in it that is identifiable as Gatwick. Meanwhile the police are frustrated in their search for the drone operators, who like their drone, prove difficult to pinpoint

During the third night a pair of arrests are announced, a local couple. The police have saved the day, the culprits are under lock and key. Everyone breathes a sigh of relief, the airport re-opens, and that’s the end of that. Except of course it isn’t, because inconveniently the pair are found to be blameless and released. When pressed during an interview, a police spokesman then makes the embarrassing admission that there is a possibility that there may never have been a drone at all.

You Couldn’t Make It Up

If these are the drone parts they've found, they're doing it wrong. Francis Wood [CC BY-SA 3.0]
If these are the drone parts they’ve found, they’re doing it wrong. Francis Wood [CC BY-SA 3.0]
You might imagine that this was the fictional plot of a thriller novel, but sadly not. All of the above is a tale of the last few days of events in the British news, save for most of the first paragraph which is our guess at how the first drone sightings may have happened. At the time of writing there remains the possibility that there could have been a drone over Gatwick, but given the current dearth of evidence it is one that seems tenuous. There are reports of drone wreckage, but since readers with long memories will recall UK police once identified RepRap parts as a 3D printed gun we’ll wait until we see it before we call it that.

If there was indeed a drone then of course we would like to see its operators brought to justice forthwith. But what concerns us at Hackaday are the implications the episode could still have for those of our community with an interest in multirotors. The usual clamour was made for Government to do something about it, and we know that would have meant a fresh set of onerous regulations for responsible multirotor owners while doing nothing about the criminals, because of course criminals have little regard for laws.

So if we are to glean anything from this sorry mess, we must examine it from several angles. Why is there a lack of drone detection technology in place? How should drone reports initially be treated and investigated on the ground? How should they be dealt with in official inquiries, and how then should lawmakers see them? This will inevitably have a British flavour to it because of the incident in question, but the points are just as valid worldwide.

When a Drone Report Comes In, We Need a Reliable Way to Evaluate It

An oft-shared drone identification guide for airline pilots, of uncertain provenance (phantompilots.com).

When we are told something new, it passes a process of evaluation in our minds. We look at the source, and weigh up the story itself. If a guy with crazy hair in the street tells us that the aliens have landed and are controlling the Prime Minister with a ray gun, it will probably be discounted. But if Hackaday tells us that someone has hacked a VGA chipset to work as a software-defined radio we’re guessing most of you would be very interested indeed.

When a fresh drone incident is reported it appears that this evaluation process has historically been defective. We have previously discussed official incident reports that come with no physical evidence of a drone, but contain descriptions of drones with capabilities unmatched even by jet fighter aircraft. It seems like any eyewitness report in which the culprit is named as a drone is automatically taken at face value no matter how unlikely it may be. The fact that a report may have come from a pilot is sometimes mentioned as a boost to its credibility, but that is a false assumption. A pilot who is not familiar with either how drones appear from a distance or what the capabilities of a drone are in the air can only be considered an unreliable witness, because while they may know a lot about aircraft they lack the required expertise for this judgement. So what can be done to help boost the quality of reporting and to immediately highlight credible reports while requiring more for dubious ones?

In the case of a near miss in open airspace there may be little effect on ground-based facilities, but at an airport such as Gatwick there can be no chances taken by the authorities. A drone collision on an aircraft on final approach could cause hundreds of fatalities, so upon receipt of a report they must have had little choice but to close the runways. There appears to have been a lack of drone detection technologies in place at Gatwick which means that the only source available to the airport would have been the eyewitnesses themselves, and since we have amply demonstrated the potential for eyewitness reports being unreliable then the current confusion becomes an inevitability. It is imperative that more reliable detection technologies be fitted or developed if necessary. This is especially true when precautionary shut-downs stretch past minutes or hours into world-news-making delays as happened in this instance.

Competent Police Investigations and Responsible Journalism on Drone Reports

The mass media tech story cycle. Our apologies to Gartner. Curve image: Jeremykemp [ CC BY-SA 3.0 ]
The mass media tech story cycle. Our apologies to Gartner. Curve image: Jeremykemp [ CC BY-SA 3.0 ]
Once an incident has started and news of it emerges there is a consequent effect upon members of our community. Legitimate drone fliers away from the airport will find themselves under more scrutiny, and since it is already a common tale to hear of police being called when flying is under way that means they could face harassment and wrongful arrest. Indeed though we do not know all the details of the pair arrested near Gatwick it smacks of their being arrested in a round-up of convenient local drone enthusiasts rather than as a result of meaningful investigation. That the names of the pair were leaked and they became the subject of a media frenzy further shows the danger in which they were placed, as well as the irresponsibility of the reporters who covered their plight.

Perhaps Most Importantly: We Need Accurate Official Incident Reports

Whatever happens in a drone report, whether it be an arrest or an embarrassing debacle, there will inevitably be an official incident report from the Civil Aviation Authority, the regulator of British civilian airspace. This will form the official record of the event, and thus should strive to be as accurate as possible, but here the process falls short for the final time. There appears to be no evaluation step performed on the available evidence and no requirement for physical proof. So if an eyewitness reports behaviors about the drone that no drone ever built could possibly be capable of, it is solemnly recorded as fact. Our previous article on this subject highlights multiple such accounts, and this is an important point because as the official record these reports are what informs legislators. When they make laws pertaining to drones it is imperative that their decisions are based upon accurate evidence, and it is clear that this is not the case. Given that they will no doubt be reviewing drone legislation in the wake of this fiasco it is particularly important that the investigators consult people with specialist knowledge in the field, demand physical proof rather than heresay, and most importantly question accounts that stretch credibility.

It seems obvious that the multirotor hobbyist is caught in a perfect storm of incompetent authorities, deeply flawed investigations, shoddy journalism, and clueless legislators. This incident has laid bare some of the shortcomings, and it is to be hoped that a few lessons might be learned to produce less of a debacle surrounding future drone incidents. It is still a developing story so there may be a breakthrough and the whole narrative will change, and if that turns out to be the case then we hope they find the correct perpetrator this time and send them away at Her Majesty’s pleasure for a very long time. We’re guessing though that every effort will be made to push it as far under the carpet as possible to save red faces among officialdom. As multirotor enthusiasts we must keep the issue of poor investigation alive though, for if we let it be buried once more it will come back to trouble us again.

London Gatwick Airport Shuts Its Doors Due To Drone Sighting

If you could pick a news story you would prefer not to be woken with, it’s likely that a major airport being closed due to a drone sighting would be high on the list. But that’s the news this morning: London’s Gatwick airport has spent most of the night and into the morning closed due to repeated sightings. Police are saying that the flights appear to have been deliberate, but not terror-related.

We’ve written on reports of drone near-misses with aircraft here back in 2016, and indeed we’ve even brought news of a previous runway closure at Gatwick. But it seems that this incident is of greater severity, over a much longer period, and even potentially involving more than one machine. The effect that it could have on those in our community who are multirotor fliers could be significant, and thus it is a huge concern aside from the potential for mishap in the skies above London’s second largest airport.

It is safe to say that if there was indeed a multirotor above Gatwick last night then its operator should be brought to justice and face the appropriate penalty without delay. Responsible fliers are painfully aware of the rules involving multirotor flight, and that airports of any description are strictly off-limits. It matters not whether this was a drunken prank or a premeditated crime, we hope you’ll all join us in saying that anybody flying outside the law should be reported to the authorities.

Continue reading “London Gatwick Airport Shuts Its Doors Due To Drone Sighting”

An Englishman’s Home Is His (Drone-Defended) Castle

Retiring to the garden for a few reflective puffs on the meerschaum and a quick shufti through the Racing Post, and the peace of the afternoon is shattered by the buzz of a drone in the old airspace,what! What’s a chap to do, let loose with both barrels of the finest birdshot from the trusty twelve-bore? Or build a missile battery cunningly concealed in a dovecote? The latter is what [secretbatcave] did to protect his little slice of England, and while we’re not sure of its efficacy we’re still pretty taken with it. After all, who wouldn’t want a useless garden accoutrement that conceals a fearsome 21st century defence system?

The basic shell of the dovecote is made from laser cut ply, in the shape of an innocuous miniature house. The roof is in two sliding sections which glide apart upon servo-controlled drawer runners, and concealed within is the rocket launcher itself on a counterweighted arm to lift it through the opening. The (toy) rocket itelf is aimed with a camera pan/tilt mechanism,and the whole is under the control of a Raspberry Pi

It’s understood that this is a rather tongue-in-cheek project, and the chances of any multirotors falling out of the sky are somewhat remote. But it does serve also to bring a bit of light back onto a theme Hackaday have touched upon in previous years, that of the sometimes uneasy relationship between drone and public.

Fail of the Week: Two Rotors Are Not Better Than Four

Fair warning: [Paweł Spychalski]’s video is mostly him talking about how bad his “dualcopter” ended up. There are a few sequences of the ill-fated UAV undergoing flight tests, most of which seem to end with it doing a reasonable impression of a post-hole auger. We have to admit that it’s a pretty poor drone. But one can only truly fail if one fails to have some fun doing it, [Paweł] enjoyed considerable success, at least judging by the glee with which he repeatedly cratered the craft.

The overall idea seems to make sense, with coaxial props mounted in the middle of a circular 3D-printed frame. Mounted below the props are crossed vanes controlled by two servos. The vanes sit in the rotor wash and provide pitch and roll control, while yaw and thrust are controlled by varying the speeds of the counter-rotating props. [Paweł] knew going in that this was a sketchy aerodynamic design, and was surprised it performed as well as it did. But with ground effects limiting roll and pitch control close to the ground, the less-than-adequate thrust due to turbulence between the rotors, and the tendency for the center of mass and the center of gravity to get out whack with each other, all made for a joyously unstable and difficult to control aircraft.

Despite the poor performance, [Paweł] has plans for a Mark II dualrotor, a smaller craft with some changes based on what he learned. He’s no slouch at pushing the limits with multirotors, with 3D-printed racing quad frames and using LoRa for control beyond visual range. Still, we’re sure he’d appreciate constructive criticism in the comments, and we wish him luck with the next one.

Continue reading “Fail of the Week: Two Rotors Are Not Better Than Four”

Watching the Watchers: Are You The Star Of an Encrypted Drone Video Stream?

Small aircraft with streaming video cameras are now widely available, for better or worse. Making eyes in the sky so accessible has resulted in interesting footage that would have been prohibitively expensive to capture a few years ago, but this new creative frontier also has a dark side when used to violate privacy. Those who are covering their tracks by encrypting their video transmission should know researchers at Ben-Gurion University of the Negev demonstrated such protection can be breached.

The BGU team proved that a side-channel analysis can be done against behavior common to video compression algorithms, as certain changes in video input would result in detectable bitrate changes to the output stream. By controlling a target’s visual appearance to trigger these changes, a correlating change in bandwidth consumption would reveal the target’s presence in an encrypted video stream.

Continue reading “Watching the Watchers: Are You The Star Of an Encrypted Drone Video Stream?”

The Zombie Rises Again: Drone Registration Is Back

It’s a trope of horror movies that demonic foes always return. No sooner has the bad guy been dissolved in a withering hail of holy water in the denoeument of the first movie, than some foolish child in a white dress at the start of the next is queuing up to re-animate it with a careless drop of blood or something. If parents in later installments of popular movie franchises would only keep an eye on their darn kids, it would save everybody a whole lot of time!

The relevant passage can be found in section 1092(d) of the National Defense Authorization Act, on page 329 of the mammoth PDF containing the full text, and reads as follows:

(d) RESTORATION OF RULES FOR REGISTRATION AND MARKING OF UNMANNED AIRCRAFT
.—The rules adopted by the Administrator
of the Federal Aviation Administration in the matter of registration
and marking requirements for small unmanned aircraft (FAA-2015-
7396; published on December 16, 2015) that were vacated by the
United States Court of Appeals for the District of Columbia Circuit
in Taylor v. Huerta (No. 15-1495; decided on May 19, 2017) shall
be restored to effect on the date of enactment of this Act.

This appears to reverse the earlier decision of the court, but does not specify whether there has been any modification to the requirements to prevent their being struck down once more by the same angle of attack. In particular, it doesn’t change any of the language in the FAA Modernization Act of 2012, which specifically prevents the Agency from regulating hobby model aircraft, and was the basis of Taylor v. Huerta. Maybe they are just hoping that hobby flyers get fatigued?

We took a look at the registration system before it was struck down, and found its rules to be unusually simple to understand when compared to other aviation rulings, even if it seemed to have little basis in empirical evidence. It bears a resemblance to similar measures in other parts of the world, with its 250 g weight limit for unregistered machines. It will be interesting both from a legal standpoint to see whether any fresh challenges to this zombie law emerge in the courts, and from a technical standpoint to see what advances emerge from Shenzhen as the manufacturers pour all their expertise into a 250 g class of aircraft.

Thanks [ArduinoEnigma] for the tip.