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A Sensor Web for Runways

Runways. Those bleak stretches of concrete that are heavily used by aircraft taking off and landing day in, day out. There's nothing actually on them other than the planes, so they seem an odd place for a sensor network to be deployed.

In truth it is precisely because there is nothing on them that a sensor web is necessary. Rather, it is precisely because we have to ensure there is nothing on them. An aircraft taking off or landing is under a lot of stress, a bit like a rubber band pulled to the limits of it's engineering. If all goes as planned, the take off or landing goes smoothly and the stress is reduced significantly.

If however, the plane hits an object on the runway, its like being jogged whilst that band is stretched between your fingers: all hell breaks loose, and the forces are unleashed. Worse, if a part falls off a plane under stress – and this has been known to happen quite often – then there's a risk that the next plane using the runway will find it, in the worst way. That is, unless the dedicated human teams spot it first. This they usually do. However, human eyes and concentration are not exactly infallible.

It might have happened over ten years ago now, but most people can still recall the Concorde crash: the TV images showing the supersonic jet with flames streaming from its tail were unforgettable. It was a piece of metal lying on the runway during take-off that caused the accident. The aircraft’s tire burst as it rolled over the metal, sending chunks of rubber flying into the fuel tank, which then exploded – with the loss of 113 lives. To avoid accidents such as this, airport staff drive up and down runways at six-hour intervals looking for any pieces of debris. But to monitor the huge areas in question without any kind of technical assistance is time-consuming and error-prone work – especially in bad weather, for instance when fog is obscuring the view. And the intervals between checks are also too long.

A single one of the sensors. They function as a network, never alone.

A new weatherproof safety system will in future monitor runways continuously for debris and warn of any dangers. Research scientists at the Fraunhofer Institutes for High Frequency Physics and Radar Techniques FHR and for Communication, Information Processing and Ergonomics FKIE are developing the system in conjunction with the University of Siegen, PMD Technologies GmbH and Wilhelm Winter GmbH in a project dubbed LaotSe – short for “Airport runway monitoring through multimodal networked sensor systems.“ “Our technology would have prevented the Concorde tragedy from happening,” says Dr. Helmut Essen, who heads the Millimeter-Wave Radar and High Frequency Sensors department at the FHR in Wachtberg. “Devices installed all along the runway continuously scan the surface. They can detect even the smallest of items, such as screws, but the system will only issue a warning if an object remains on the runway for a longer period of time. A windblown plastic bag or a bird resting briefly will not set off the alarm.”
The system comprises an infrared camera, optical 2D and 3D cameras and networked radar sensors. These sensors were developed by researchers at the FHR. The three different types of equipment complement each other: Radar functions around the clock and whatever the weather. It can detect objects but not identify them.

The cameras can identify objects using machine vision or human eyes, but in inclement weather or poor visibility, they struggle to detect them. It is thus a perfect partnership. The radar systems sweep the runway looking for anything that should not belong, even sweeping whilst the plane is rumbling past. If they detect anything, the 2D camera is focussed on the object, with 3D coming into play from multiple angles, to detect the shape of the object and make a positive identification.

The infrared camera takes over from the opticals in night operations, or other poor visibility scenarios. If all else fails, the radar can still identify that there is something on the runway, even if it cannot tell that the 'object' is a bird. However, if visibility is so poor the cameras are not working, it is better safe than sorry, anyway.

While similar radar systems have been developed, these are only capable of detecting metal objects, and they often give rise to false alarms. What is more, because they are mounted high up on masts they can easily be damaged in the event of an airplane accident. Dr. Essen outlines some of the new system’s advantages: “Our radar sensor transmits at a frequency of 200 GHz, so it can detect objects that are just one or two centimetres across. And using three different kinds of sensor means false alarms are almost out of the question. The device is miniaturized and scans up to 700 meters in all directions.”

Initial testing of a radar sensor and camera will begin at Cologne-Bonn airport this autumn, and plans are in place for further testing using several demonstrator systems.


Making runways safer

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