Defense against drones

Drones are useful, but they can also be dangerous if misused for terrorism. Fraunhofer is developing technology designed to serve as a defense against unmanned aerial systems.

Civil security research

Defense against drones – the danger on the radar screen

Drones are practical and can be put to use for almost any purpose. They help rescue teams survey sites, they assist farmers inspecting their fields, they are the preferred method of extreme athletes for taking selfies from the sky, and they give the term “air mail” an entirely new meaning, as they begin to deliver us letters and packages. However, they can also be put to use for criminal and terrorist purposes, such as spying on people and objects, smuggling drugs and weapons into prisons, as well as terrorist attacks on people, vehicles or buildings. Here, we are referring to unmanned aerial vehicles (UAVs and/or UAS for unmanned aerial system), also referred to as drones in every day usage.

Drones are becoming more and more powerful. In recent years the possible altitude, range, endurance, air speed and precision of navigation has risen appreciably. In addition, they can transport increasingly more mass. Moreover, drones are cheap, easy to obtain and also available as a kit. It is no wonder that their popularity is growing, both in the commercial and private sectors. German air traffic control authorities are working on the assumption that there will be more than one million drones in Germany by 2020.

At the same time the number of incidents is on the rise: drones enter no-fly zones, e.g. at the airport or major events such as rock festivals or football matches. Up to now such incidents have primarily involved mere negligence or indiscretion, if the drones of hobby pilots come dangerously close to aircraft or illegally record videos and take photos of persons or buildings. Yet drones can also be used for specific terrorist purposes. Consequently, German security authorities are alarmed, as no effective defense system has been devised to date.

The danger that can be posed by drones was illustrated by an event that took place in 2014, when a drone with a flag displaying Greater Albania was suddenly seen floating above the football field in Belgrade during the European Football Championship qualifier between Albania and Serbia. This led to riots, resulting in the entire game having to be called off. Instead of a harmless flag, however, terrorists could also have flown bombs into the stadium, and subsequently dropped them into the crowd. Defense against drones comprises a three-step approach. The first step involves discovering the drone. Taking into account the high speed of the flying objects and the limited recognition radius of sensor technology, this alone presents a challenge. The second step involves recognizing just what type of drone it is and whether it represents any type of danger. Perhaps the thing hovering and buzzing so ominously above the starting field of the city marathon is just the camera drone of the local TV channel.

If the flying object is identified as a dangerous drone, then the third step kicks in: that of countermeasures. These must be carefully planned. What is the model? What is the speed of the drone? What is its maximum permitted load? At what radio frequency is it being controlled? All this analysis and information needs to be made available with a rapidity that approaches that of real time. This is because, in case of an emergency, only a few seconds would be left to make the correct decision and introduce appropriate defensive countermeasures.

Distinction is made between passive and active measures, in the latter case also between soft or hard measures. Passive measures are limited to, e.g., triggering an alarm. Active measures present a challenge to both the personnel and the technology involved, because every intervention is precarious and the legal consequences thereof must be precisely weighed. So-called “jamming” is an example of a soft measure. In such a case signals are sent out that interrupt the radio connection of the drone to the party controlling it, thereby forcing it to land. Yet this only works if the drone has been programmed to land under such circumstances. There is a danger that it will nonetheless continue to fly uncontrollably and then crash. By contrast, in the case of “spoofing” the drone is sent a factitious and incorrect GPS signal, in order to cause it to change its course.

Examples of hard defense would be physically intercepting or shooting down the drone. Such a measure would only be turned to as a last resort, because of the danger of harming innocent persons. There is a wide choice among methods to be used: shooting the drone down with a laser, water cannon or a gun, the use of kamikaze drones, employment of a safety net or an adhesive that renders the drone incapable of flying, interference by means of a powerful acoustic sound or through a tether.

There is a variety of conceivable threatening situations. As a result, Fraunhofer researchers and their partners rely on a variety of approaches and technologies. For detection and identification purposes, sensor technologies such as radio, acoustics, radar, and/or infrared and electro-optics are employed. Under ideal circumstances the sensors would serve to complement one another, but there is not yet any sensor that can detect everything. Each sensor has its strong and weak points. Visual-optic sensors do not function at night or if there is rain and fog. In such a case, infrared or radar would be a better choice. If it is a question of the range of detection, then radar is superior to visual optic sensors and infrared sensors.

BMBF-promotion of civil security

The detection modalities implemented in the context of "AMBOS" include, among others: the acoustic bearing, location and classification of drones using microphone arrays.
© Fraunhofer FKIE

The detection modalities implemented in the context of "AMBOS" include, among others: the acoustic bearing, location and classification of drones using microphone arrays.

Four-channel MuRPS (Multi-channel Radar for Perimeter Surveillance) with quadcopter in the background.
© Fraunhofer FHR

Four-channel MuRPS (Multi-channel Radar for Perimeter Surveillance) with quadcopter in the background.

In order to prevent and combat terrorism the Federal Ministry of Education and Research (BMBF) has initiated the “Research for civil security” program through which it will be funding ten collaborative projects with over 21 million Euros, including the four projects AMBOS, ArGUS, ORAS and MIDRAS, with the goal of defense against unmanned aerial systems. The Fraunhofer Institute for Communication, Information Processing and Ergonomics FKIE, the Fraunhofer Institute of Optronics, System Technologies and Image Exploitation IOSB, the Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, HHI and the Fraunhofer Institute for High Frequency Physics and Radar Engineering FHR are significantly involved and bring their core skills to bear on the work involved. Three technical areas play an especially important role here: radar engineering and optronics for signal and image acquisition, data fusion and image analysis for processing and information retrieval from images and videos, human/machine interfaces, as well as system technology for the development of complex systems.

The interaction of different sensors is crucial for a successful defense. Sensor data fusion is the special feature of the German-Austrian joint project AMBOS of Fraunhofer FKIE. All sensor data is analysed by means of an algorithm, the results of which provide information as to the type and nature of the targeted object. The researchers are especially proud of the fusion engine. This first collects the data provided by the individual sensors, which has been prepared by algorithms, therefore data that has been adjusted to a certain extent.  Sophisticated software combines the data and determines whether one is really dealing with a drone and if so, what type of drone. The detailed information is clearly presented and visualised in a situation image representation that serves as a basis for further action and choosing the preferred measure of active intervention based on the situation and the level of threat. One option would be to disturb the radio remote control, satellite navigation or on-board electronics of the drone. At the same time AMBOS is developing a net launcher for use with dangerous flying objects.

In the ArGUS project, Fraunhofer IOSB focuses on a sophisticated assistance system for decision support. The IOSB developers consequently focus on a simulation-based prediction of situations designed to help users make decisions. It is, after all, a question of preparation of how to present information to a decision maker quickly and without cumbersome handling. This is because at speeds of 100 km/h and with a range of a few hundred meters a drone is capable of reaching a possible target in just a matter of seconds. If the drone may be carrying explosives, then there is little time to decide about countermeasures. The system is designed to show which actions can be performed by a drone, which countermeasures may lead to success and with what level of probability, as well as the risk connected therewith. However, in the final analysis it is man and not the machine making the decision.

Most drones are radio-controlled and can be detected with radio sensors. But there are also self-sufficient drones that are automatically started by timers and therefore cannot be detected by means of radio sensors. Apart from visual-optical and infrared sensors, radar technology can also be used, as in the ORAS project of the Fraunhofer FHR. Millimetre wave radar is ideal for monitoring in the immediate vicinity. Unlike cameras, radar is an active sensor that “illuminates” the scene independently and therefore works reliably even in the dark, rain, fog, dust or smoke. Such a system can be permanently installed or employed on a mobile basis. ORAS is based on a network of distributed radar sensors and optical cameras that follow the terrain contour. This makes it especially suitable for use in confusing environments such as event venues in inner cities, or critical infrastructures such as airports and power plants. ORAS ascertains the signature of the drones and the speed of their rotor blades. As a result, false targets such as birds can be reliably detected and conclusions can be reached about the load through comparison with databases and by means of optical sensors. The system is capable of locating and tracking multiple drones simultaneously.

Fraunhofer HHI is a project partner in the fourth funded project MIDRAS. The work of the Institute concentrates on the detection of and defense against micro-drones. The researchers at Fraunhofer HHI use so-called massive MIMO antennas with a high transmission quality and data rate, in order to precisely locate the position of micro-drones and if necessary, to interfere with or influence them.

Modular drone detection and assistance system (MODEAS)

MODEAS
© Fraunhofer IOSB

Fraunhofer IOSB is developing an independent project named MODEAS that constitutes a complete system that covers the entire chain from detection to intervention. The system works with different types of sensors. Four high-resolution digital cameras, each equipped with 25 mega-pixel sensors, generate a 360-degree all-round view. Telephoto zoom cameras, directional microphones and laser rangefinders are used to track incoming flying objects. All data is visualised in a mobile control centre. The system can be conveniently configured and operated via a graphical user interface. Each MODEAS station has an optical range of up to 500 metres. In combination with radar technology the range increases to several kilometres.

Yet all warning systems must deal with a vexatious problem: false alarms. A false alarm can be triggered by birds, as well as by the camera drone of a regional TV station or a drone that is being used by the police for surveillance. To avoid such false alarms to the greatest extent possible, the Fraunhofer experts have developed a database, in which the features, as well as the visual optical and infrared signatures of many drone models are stored. When sensors detect a drone, the system compares the sensor data with the databank in real time. Ideally, the flying object will be immediately classified in a quick and reliable fashion. The software then displays information such as the maximum load and speed of the flying object. This information makes it possible to draw further conclusions about potential dangers and what defense measures to initiate.

Sensors of the future

In security technology, it is important that various types of sensors are used to cover the broad technical spectrum of drones and to function reliably in different operational scenarios. Human sensory organs are comparable in this regard. Under ideal circumstances they serve to complement one another, but in an emergency they can also be used individually to provide a life-saving impulse. In security technology, many different types of sensors create a system of defense with increased resilience. Drone defense systems that are also capable of performing effectively in the future must therefore have an open architecture that is so flexible that even completely new types of sensors can be integrated. One such example would be a laser vibrometer for long-distance detection. This sensor “scans” the drone and detects vibrations based on the Doppler Effect. If the modulated frequency spectrum has characteristic features, it can then be identified through comparison with a previously created database. In some cases it is also possible to measure whether the drone is carrying a load, since a drone carrying cargo has a different vibration than one that is not loaded. Knowledge to this effect can be an important factor in the choice of a defense measures. Fraunhofer scientists are seeking to devise laser vibrometers suitable for use with drones.

Another plan in the works for defense against drones is the so-called “laser-gated viewing sensor.” This sensor suppresses visual disturbances. This would make it possible to even discover drones under difficult viewing circumstances, e.g. at night, or when they are behind bushes, or concealed in smoke or fog. Such sensors would function in a manner involving the interaction between pulse laser beams in the nanosecond range and cameras with an accurately adjustable shutter interval (gate). This would make it possible to separate a located target from the background while also suppressing the foreground.  

 

Intelligent swarms of drones

The trend in drone development is in the direction of swarm intelligence. With the help of complex control algorithms, they can learn how to fly like a flock of birds in formation, to avoid obstacles and to pursue targets independently. The achievements of these small flying robots have been demonstrated through trials conducted by the U.S. Department of Defence, which successfully tested a swarm of 103 micro-drones that were given the task of carrying out reconnaissance on a piece of terrain in California during October 2016. The autonomously acting drones behaved like a collective organism that was able to guide itself.


These examples demonstrate the importance of the interdisciplinary collaboration of science, business and government in the area of security research. It is not just technology, but also legal and ethical issues that play a significant role when the goal is to convert innovative developments into application-oriented solutions. 

Projects for the defense against drones

Defense against unmanned flying objects for authorities and organizations with security tasks (AMBOS)

Fraunhofer Institute for Communication, Information Processing and Ergonomics FKIE

In the joint German-Austrian project “AMBOS,” since February 2017 a total of twelve partners from science and industry have been developing a system that recognizes drones, analyses their risk potential and – to the extent necessary – carries out defensive measures. As future users of the system, five German security authorities, including the Federal Criminal Police Office (BKA) and the Federal Police are associated with the bi-national research project as partners. AMBOS is funded by the German programme “Research for civil security” of the German Federal Ministry of Education and Research (BMBF) and the Austrian “Support programme for security research – KIRAS” of the Austrian Federal Ministry for Transportation, Innovation and Technology (BMVIT).

 

Assistance system for situation-aware defense against dangers from unmanned aerial systems (ArGUS)

Fraunhofer Institute of Optronics, System Technologies and Image Exploitation IOSB

The »ArGUS« system detects unmanned aerial systems and generates proposals for legally secured countermeasures. The partners in ArGUS are Verband für Sicherheitstechnik (Association for Security Technology) VfS, Hamburg, the  European Aviation Security Center (EASC), Schönhagen at Berlin, die two industrial companies Securiton GmbH (Achern) and Atos Deutschland, as well as the Deggendorf Institute of Technology and the Johannes Gutenberg University  Mainz. Associated partners from the area of application are the Frankfurt Airport, the Hamburg security service provider Power Personen-Objekt-Werkschutz GmbH, the Bavarian state criminal police agency and the Federal Criminal Police Office. 

 

Sensor-based monitoring and alerting system for the detection and tracking of unmanned aerial systems (ORAS)

Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR

The “ORAS” system seeks to detect unmanned aerial systems in urban environments. Intenta GmbH is developing novel pivoting optical sensors, which, in conjunction with the radar network designed by Fraunhofer FHR and with a 360° Domradar from Spinner GmbH, will form a tight-knit monitoring network for unmanned aerial systems. In the control centre designed by ASINCO GmbH several UAS can be reliably located and tracked. ORAS is designed to be easily integrated into threat intervention planning. Such a system could conceivably be used for a variety of operational scenarios, e.g. in a mobile fashion for the protection of public festivals or major events all the way to permanently installed systems for the surveillance of critical infrastructures such as airports or power plants. Legal issues as well as the economic potential of the system concept have been elucidated by the Technical University of Applied Sciences Wildau.  

 

Micro-drone defense system (MIDRAS)

Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, HHI

In the context of the "MIDRAS" project, Fraunhofer HHI has undertaken the development and integration of massive MIMO antennas. These will be used for the spatial detection of micro-drones as well as for targeted interference.

 

Modular Drone Detection and Assistance System (MODEAS)

Fraunhofer Institute of Optronics, System Technologies and Image Exploitation IOSB

“MODEAS” consists of a flexible number of coupled sensor stations that can easily be customized to specific tasks. These stations are equipped with high-resolution all-round optical vision sensors as required, tracking units with optical telephoto zoom cameras, directional microphones and laser rangefinders.