The key to detecting tiny drones spying on military bases or intruding into an airport's airspace could be to use an existing TV signal.

Canada's Department of National Defence is exploring using regular television signals to create a radar system that would detect flying intruders the size of an insect, as well as using other drone detection technologies.

The military is worried about spying drones collecting real-time video of its operations as the machines become smaller, cheaper and more expendable.

And the chaos caused by drones flying into airspace at Britain's Gatwick Airport this week shows the small devices can have big consequences.

As drone technology has evolved, drone detection techniques need to keep pace. Some drones have even been fashioned to look like birds to help them better blend into the environment. Others are equipped with gripping claws allowing them to perch on a tree limb or ledge for better surveillance, according to a reference document written in 2016 by Defence Research and Development Canada (DRDC), a DND agency.

"Small drones are increasingly being used for spying/reconnaissance applications. They are small in size and hard to detect," said the document titled, Counter-measures against drone surveillance.

This is a drone made to look like a female falcon, but it's not used for spying. It's to drive real birds away from the Edmonton International Airport. (John Robertson/CBC) "They can pose real and significant threats to military operations," it stated.

How radar detection system works

To counter that threat, DND has been researching how to better detect spying drones with DRDC examining several different technologies.

According to the document, one of the best solutions found was to create a passive radar detection system using TV signals.

The system works by monitoring the constant TV signals in the air. When these signals hit an object, they can be detected by the system.

"Firstly, TV signals transmitted by major TV channels are powerful enough for detecting drones, even very small ones," said the DRDC document.

TV signals transmitted by major TV channels are powerful enough for detecting drones, even very small ones. - Document from Defence Research and Development Canada, an agency of DND

"Since TV transmission towers have been a fixture in the urban landscape for a long time, people are used to and accepting their presence.

"Secondly, TV signal is free of charge: there is essentially no cost for tapping into the TV signal transmission.

"Thirdly, TV signals are transmitted continuously 24/7, making it an ideal source for radar surveillance application."

The researchers suggest the TV transmitter at Camp Fortune in Ottawa could be used to monitor high-value infrastructure in a 17-kilometre radius. It would even be able to pick up insect-sized drones operating within a five-kilometre radius around the Ottawa International Airport.

Battery-operated drones with a range greater than 50 kilometres are already available on the commercial hobby market, according to Defence Research and Development Canada, a DND agency. (Sarawut Chamsaeng/Shutterstock)

Other ways of detecting drones

But the technology does have its flaws. Any radar system that can pick up small drones can pick up birds as well, both of which have similar radar signatures that could result in false alarms.

However, the document suggests this problem may soon be solved by artificial intelligence algorithms that can tell the difference between a bird and a drone by analyzing the different ways they move.

There's no perfect solution. Each of them has their strengths and weaknesses. - Charles Vidal, a research engineer with the National Research Council

The military isn't alone in looking to develop better ways of detecting drones. The National Research Council of Canada has been examining drone detection technology for the last three years.

It has looked at a range of different ways to locate drones, including advanced radar that's good at detecting small objects, acoustic technology that can recognize drone sounds and a radio frequency detection system that tracks down the radio signals exchanged between a drone and its operator.

Charles Vidal is a research engineer with the National Research Council. (Noémie Moukanda/Radio-Canada)

Engineers also explored using thermal imaging cameras to highlight a drone's heat signature and advanced cameras that can spot drones from far away.

"There's no perfect solution. Each of them has their strengths and weaknesses," said Charles Vidal, a research engineer with the National Research Council.

Much demand from other sectors

Vidal said there's a lot of demand for this kind of technology from many different sectors.

Industrial sites like oil refineries want to keep drones away from dangerous equipment. Even jails and prisons want to locate drones to keep them from dropping contraband into their institutions.

But airports contacted by CBC News haven't embraced these new technologies, even though the number of drones spotted too close to airports and aircraft in Canada more than tripled between 2014 and 2017 from 38 to 135. There have been 95 incidents reported to Transport Canada this year, as of Nov. 30.

Toronto Pearson International Airport said in a statement earlier this month that it is not currently investigating the use of drone detection systems. The spokesperson went on to say that drones are "not much of an issue" around the airport at present.

However, it will continue to monitor drone activity near the airport and respond accordingly.

Vidal says companies that run industrial sites are interested in ways to detect drones to keep them away from dangerous areas. (FS11/Shutterstock)

The Billy Bishop Toronto City Airport is taking a similar approach. It's monitoring the availability and usage of devices to detect drone activity near the airport, but hasn't yet used that technology.

In 2016, a plane en route to Billy Bishop had a close call with a drone and had to take evasive action to avoid it. Two flight attendants ended up with minor injuries.

Under Canadian law, drones can't be flown within 5.6 kilometres of airports or 1.9 kilometres of heliports. Endangering aircraft is a particularly serious offence that can carry fines of up to $25,000 or possible prison time.

In Nova Scotia, a spokesperson for the Halifax Stanfield International Airport said it doesn't make public what kind of detection technology it does or does not have.

Still, Vidal said there are others willing to adopt the new drone detection technologies.

"Different organizations are already performing pilot projects where they will deploy these solutions for either a short period of time for testing and evaluation," he said. "These systems are getting deployed more and more."

Different organizations are already performing pilot projects where they will deploy these solutions for either a short period of time for testing and evaluation. - Charles Vidal

The DRDC document recommends hands-on testing as well.

Its authors wanted the DRDC to start an in-house project to develop prototype detection systems.

The DND has not said what kind of technology it has adopted or might adopt to detect drones.

No one from the department would agree to an interview.

In an emailed statement, the department said it will continue to examine the threats drones pose and will keep evaluating existing drone detection systems and countermeasures, including "potential physical, electromagnetic and other protection improvements."