When drones fly beneath the radar

Drones offer many benefits, but unfortunately they provide terrorists and criminals with new opportunities, so they need to be monitored. The Danish company Weibel Scientific A/S has now developed its first radar system for monitoring drones.

The expression ‘flying beneath the radar’ is used idiomatically so often that you almost forget the original meaning—but not at Weibel Scientific.

“A drone is capable of flying so low that it is not picked up by many traditional radar systems. At the same time, it is difficult to detect on account of its small size,” says Weibel CEO Peder R. Pedersen.

The company, which is located to the north of Copenhagen, was established on the basis of research originally carried out at DTU. In 1977, Erik Tingleff Larsen resigned from his position as an associate professor at DTU Electrical Engineering to form the company, which is now one of the world’s leading suppliers of advanced radar systems. One of the first employees was Peder R. Pedersen, who did his DTU Master’s project at Weibel in 1983. This led to a PhD project, followed by permanent employment, and then in 2002 he was appointed CEO. When Peder Pedersen started working for Weibel, there were seven employees—now there are 100, of whom 35 are engineers. And the company needs more.

“We definitely expect to take on more engineers in future. There is a growing demand for radar systems, largely for tracking drones. We recently started to sell the first systems, but there is still a lot of RD work to do. Drones represent a new type of threat, one which is very difficult to counter.”

This is what the measurements look like when a Doppler radar system detects a drone. The Doppler radar tracks both the velocity and direction of movement of the object.

Praise for national drone strategy

Last year, it was revealed that inmates at Danish prisons have had mobile phones smuggled in by drone. And in the Middle East, the first attacks have taken place in which terrorists have flown drones armed with hand grenades in over market places.

“You don’t need much of an imagination to envisage how drones could be used even more dangerously. It’s obvious that protection is required, for example in connection with football matches and other events where large crowds are gathered. And the same applies to critical infrastructure,” says Peder R. Pedersen.

“It’s fantastic that, with its national drone strategy, the Danish Government has introduced a wide range of initiatives aimed at boosting the use of drones. In particular, we are very pleased with the markedly better possibilities for test-flying drones. This is a key factor when we need to demonstrate to potential customers around the world that our systems are actually capable of detecting drones effectively in practical trials,” says Peder R. Pedersen.

Several types of radar

To understand how Weibel Scientific can supply systems for drone monitoring, you have to know something about the company’s technology.

By far the majority of radars are so-called pulse radars. This applies, for example, to virtually all radars which are used for air traffic control. A pulse radar transmits a short, powerful pulse at fixed intervals, and some of this pulse is reflected by the object. By measuring the time between sending and receiving the reflected signal, it is possible to calculate the distance to the object. Pulse radar systems are good at detecting objects within a large area of the sky, and for determining the distance to the objects. On the other hand, they are less suitable for determining the objects’ velocity and direction.

Weibel’s radar systems on the other hand transmit a constant signal. They utilize the so-called Doppler effect, which is where the wavelength of a signal increases when the object transmitting it is moving away from the observer, and decreases when the object is moving towards the observer. It is this effect which causes an ambulance siren to sound differently after driving past. The effect is stronger the faster the object is moving. Therefore, a Doppler radar can determine the velocity of the object with very high accuracy based on the change in the wavelength of the signal being bounced back from the object. It is also possible to determine the direction of movement of the object to a very high degree of accuracy.

Weibel cheats physicsIn short, a Doppler radar system provides much more information about the object which has been detected. On the other hand, the textbooks would say that the Doppler radar is inferior to a pulse radar as regards covering large areas of the sky and at determining distances to objects. However, Weibel has succeeded in overcoming both constraints.

In 2003, the company combined Doppler technology and pulse technology in one and the same radar system, making it possible to determine an object’s velocity and 3D position very accurately.
“The next step was taken a couple of years ago when we were invited to bid for a job to develop two systems for 3D flight tracking in Indonesia. Traditionally, our systems have not been used for general air traffic control, but we had an idea for how we could ‘cheat physics’ so that our Doppler radar could also be used in this context,” says Peder R. Pedersen.

With the solution, the radar changes angle according to pre-programmed movements so that the desired area of the sky is scanned.

“We managed to demonstrate that the solution lives up to expectations, and we ended up winning both contracts.”

Drones difficult to monitor

It turned out that this solution is also very good for drone monitoring, which is otherwise a challenge for traditional radar systems. Peder R. Pedersen explains: “Helicopter drones are able to fly very slowly. This makes them difficult to detect using a pulse radar—but not for a Doppler radar system. Because even though the drone as a whole is moving slowly, the rotors are moving around very fast, and produce the distinctive signal in a Doppler radar.”

However, it was not plain sailing transferring the technology which had been used for the Indonesian solution to one which could be used for drone monitoring.

“In addition to their small size and the fact that they can fly extremely low, drones pose several other challenges. Helicopter drones in particular are extremely manoeuvrable. A skilled drone pilot can exploit this to conceal the drone between irrelevant objects such as trees, buildings, birds, etc.,” says Peder R. Pedersen.

Weibel Scientific therefore decided to join forces with another Danish company—Copenhagen Sensor Technology (CST), which developed an optical system which has been integrated with Weibel’s radar. By combining radar and optical sensors, it becomes much more feasible to track a drone while avoiding false alarms, for example when a bird flies past. The optical sensors also help to identify the drone.

Special competences required

“The radar system’s software is being optimized all the time. In fact, one of our engineer groups is permanently assigned to the task. And it is this area where we have the greatest problems finding enough new employees with the right competences,” says Peder R. Pedersen. “Radar algorithms are similar to those used in image processing for medical devices etc., so we are competing with other sectors for the same expertise. Sometimes, there are even projects which our customers want us to help with, but where I have to say no.”

It is relatively easy to recruit employees with microwave and mechanics competences, which are the two other main areas where Weibel employs engineers.

“Over the years, we have had a lot of Master’s students and people doing their PhD projects, and usually we have employed them afterwards,” says Peder R. Pedersen, who is a member of DTU Electrical Engineering’s Advisory Board.

“All in all, it is natural for us to recruit from DTU because of its proximity and the strong research environment within microwaves, which in effect gave birth to the company.”

Source: DTU

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