State of the Art - Group 4 - 2018/2019, Semester B, Quartile 3

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State of the Art

We now consider the State of the Art regarding the general problem description. We take a look at numerous distinct papers and patents.

Game of drones: defending against drone terrorism[1]

This article discusses the threat of weaponised drone warfare. Not only are drones UAVs that may hinder people at places like for example airports, but they can also be equipped with weaponry, and this potentially makes them extremely dangerous. Weaponised drones could be used in terrorism as they are unmanned and can be operated from a distance, meaning that no people are put at risk. However, for this same reason, it can also be used for military purposes. On November 3, 2002, the era of weaponised drone warfare began when an American drone blasted a car with a missile, killing all six occupants. Since weaponised drones form such a threat to potentially innocent people, the article lays out the three challenges to defending against drone terrorism: detecting potentially hostile drones, identifying them, and destroying or neutralising them.

The detection of drones could be done by using a radar detection system, where the location and height of a detected object in the air can be calculated. However, the critical challenge of the radar system is to determine whether such a detected object is actually a drone. Furthermore, due to the way a radar detector works, a drone can be created using materials such that it will not be detected. Therefore, there is a need for a proper identification system to classify a detected object as a potentially dangerous drone. Identification of any specific aircraft, at present, relies upon broadcasting a coded signal, which is decoded by air traffic control towers. Such that allies and enemies can be identified and to avoid targeting a friendly aircraft. As a result, all aircraft where radar service is provided should require systems that can broadcast coded signals for identification. Once a drone has been detected and identified as potentially hostile, it needs to be neutralised. Drones can be shot down, have their guidance systems damaged, or their control signals can be jammed or interfered with. Air-to-air missiles and gunfire, lasers can be an effective weapon against drones. Lastly, electromagnetic attacks that consist of interfering with the GPS signals would make the drone uncontrollable to the pilot and using 'spoofing' could enable an attacker to take control of the drone.

Investigating Cost-effective RF-based Detection of Drones[2]

The focus of the article is on the detection of a drone, such that it can be dealt with. More specifically, a drone detection system that autonomously detects and characterises drones using radio frequency wireless signals. Where two approaches are proposed, both using inexpensive technology, e.g., WiFi and inexpensive software-defined radios, to automatically detect drones. One effective method that detects drones by observing the reflected wireless signal, and a second passive method that listens to the communication between the drone and its controller. In the active method, a Wi-Fi receiver can be used to detect a drone based on the signature of the signal reflected from the propellers of a drone. Similar to radar, a transmitter broadcasts signals and a receiver captures reflected signals that bounce of a drone. The passive method detects a drone by listening to the communication channel between the drone and its controller using a wireless receiver. Usually, drones communicate with their controllers a few times per second to update their status and to receive commands from the controller. A system could collect wireless samples and observes the signal, analyse them and can then detect a drone's presence.

Clash of the drones[3]

The motivation for this article was the trouble at Gatwick Airport in London, where flights had to be diverted because a drone was spotted nearby. They stated that in the year 2017, in the UK alone, it has happened over 100 times that a drone was too close to an Airport. These events are undesirable, and thus authorities are trying to find reliable and safe strategies to take down these drones. They state that current countermeasures of taking out drones cause too much collateral damage. One option would be “Geo-fencing”, where drones would simply be fenced out due to software. However, this requires the manufacturers to implement this and the users to not tamper with this, which is considered too risky. The Dutch Ministry of Justice and Security even gave away $30.000 for the best idea to take out drones, so the desire for such technology is high.

Ideas were among others using other drones to take out the undesired drone. Other examples were using airguns to bring the drones to the ground, and training animals such as eagles to take down the drones. The consequences of drones on airports are catastrophic. Even a small drone could severely damage the windshield of an aeroplane, so there need to be forbidden zones for drones to guarantee public safety.

Small Remotely Piloted Aircraft Systems (drones), Mid-Air Collision Study[4]

The Department for Transport, the Military Aviation Authority and British Airline Pilots’ Association commissioned a study about what the consequences are of collision mid-air between a crewed aircraft and a drone. The goal of the study was to find the minimum speed at which such a collision would cause critical damage to the aircraft. An important note is that they only focused on windscreen collisions, and did not take, e.g. the motors into account. The main results of the study were that for aviation aeroplanes with windshields that were not birdstrike-certified, the damage done was critical at speeds well below the regular cruise speeds.

For airliners, their windscreens are much more resistant. For drones in the 1.2kg class, no critical damage occurred, but for drones in the 4kg class, the damage did undoubtedly occur. Another interesting remark is also that how the drone was built has a significant influence on the damage done, for example, if the motors are covered in plastic or not. Their study also concluded that drones do much more damage than regular birds at equal speeds and with equal weight. This is due to the fact that birds act more like a fluid when colliding at such speeds, whereas the drones do not act like this due to their hard materials.

Drone Safety Risk: An assessment[5]

This study, published by the Civil Aviation Authority, 2018, has investigated the likeliness of a collision between a drone and an aeroplane, as well as the consequent damage. In January 2018, there have been seven confirmed cases of a direct collision between a drone and a civil or military aircraft. Furthermore, they have estimated that the probability of a drone being in the proximity of an aircraft going at speeds high enough such that a collision could cause damage, is about 2 in a million. Furthermore, the probability of consequently causing critical damage is even lower than this probability.

They have also investigated the consequences of a drone colliding with a turbo-fat jet engine. They have concluded that a small drone would not do any significant damage. On top of that, even if it did damage, a multi-engine aircraft should still be able to land most likely. However, they also stated that helicopters are much more susceptible to drone collisions.

How do you catch a drone? With an even BIGGER drone and a giant net: Tokyo police reveal bizarre 'UAV catcher' [6]

In this article, emerging technology is discussed to take out unwanted drones. They do not only discuss the technology but also report on the fact that police have officially employed this technology in Tokyo, Japan. The technology that they use is a drone with a net attached to it, making it able to catch the unwanted drones. The primary motivation for this deployment of technology was a security breach from 2015. A man called Yasuo Yamamoto controlled a drone that contained dangerous concentrations of radioactive caesium and landed it on the roof of the Japanese Prime Minister’s Official Residence. It managed to stay there undetected for 14 days after it was accidentally discovered during a tour around the building for new employees. The goal was to raise awareness to close all nuclear reactors in Japan.

The developed counter-drones will be used to find and capture malicious drones who fly dangerously close near public officials, in fear of, e.g. a drone containing explosives. The deployment of these drones was part of a more massive project of Japan in order to strengthen airspace security. Masahiro Kobayashi, an Osaka-based lawyer, mentioned that the biggest fear raised by experts is still the possibility of uncrewed aircraft coming too close to commercial aeroplanes.

The SkyWall 100 bazooka captures drones with a giant net[7]

This article discusses a new type of technology in order to take unwanted drones out mid-air. In a nutshell, it is a bazooka which can shoot nets as far as 100 meters away. The bazooka is portable and can be operated by a single individual, meaning it is not a stationary weapon and can thus be moved from place to place. Important to note is that after the net is shot and the drone has been successfully shot, a parachute on top of the net is deployed to avoid any dangerously falling debris. The product is not meant for regular people, but the device is marketed to be deployed at sensitive events and near buildings such as an airport.

The bazooka is also equipped with an intelligent locking system to aid the controller to hit the drone successfully. They also announced the SkyWall 300, which is a remotely controlled mounted tripod with the same effect but with a further range. The SkyWall 100 was not yet available at the time of release, but nowadays it has been used multiple times, for instance at a Berlin air show in April 2018.

A literature review on new robotics: automation from love to war[8]

In this literature review, Royakkers and Est investigate the social significance of robotics for the coming years in both Europe and the US by studying robotics developments in five different areas: the home, health care, traffic, the police force, and the army. Royakkers and Est argue that our society currently accepts the use of robots to perform dull, dangerous, and dirty industrial jobs, but wonder how this will be in the future as robotics is moving more and more out of the factory. Royakkers and Est provide a literature review that `attempts to provide an engaged but sober (non-speculative) insight into the societal issues raised by the new robotics: which robot technologies are coming; what are they capable of; and which ethical and regulatory questions will they consequently raise?' Especially the areas that concern the police force and the army are useful for the problem definition we provided.

Royakkers and Est argue that police robots are still in an experimental, exploratory phase, but that the USA and Japan are way in front of Europe when it comes to the development of these robots. The two central applications are carrying out surveillance and disarming explosives. One ethical issue that Royakkers and Est bring up is a discussion about privacy versus safety. They argue that a tricky issue with robots is the violation of privacy. Moreover, there is a risk of manipulation of sound and recordings, which would be a considerable disadvantage. Furthermore, what happens if malicious attackers steal essential data stored on such a robot? The increasing deployment of police robots would also mean that police officers must acquire new skills, which costs time and money. It could also eventually lead to the loss of essential police skills as the police officers will be trained in different ways.

Furthermore, there is an essential legal complication regarding the deployment of airborne robots for police purposes. That is, it is not yet clear how they can be deployed following existing laws and regulations. Abuse and proliferation are important factors that have to be kept in mind as well. Specific safety rules will have to be met, and these robots must not pose any danger to civilians at all. What would happen if one of these robots were hacked? There could be disastrous consequences, which could then lead to even stricter legislation concerning employing these robots. That is not all. Armed police robots will raise critical ethical questions on the usage of these robots.

Developing tools to counteract and prevent suicide bomber incidents[9]

In this paper, Royakkers and Steen describe how teams of developers and designers engaged with ethics in the early phases of innovation based on case studies in the SUicide Bomber COunteraction and Prevention (SUBCOP) project. In order to achieve that goal, Value Sensitive Design (VSD) is used as a reference. The most important ideas presented in this scenario are the focus on the effectiveness, the safety, and the utility of the tool developed. That is, their ability to remove the threat, the ability to survive the threat, and the ability to properly utilise the tool. Five selected tools were developed by different teams of researchers and developers of different organisations: An Acoustic Warning Signal Projector (A-WASP), electronic countermeasures to prevent remote detonation, procedures for using electroshock devices, a system that produces a Water Mist, and a protective shield. Here, these last two are both for blast and fragmentation mitigation. These tools are aimed at various things. Some tools such as the Water Mist focuses on protecting bystanders, whereas the electroshock devices are intended to approach and engage suspects. At the end of their paper, Royakkers and Steen conclude that the researchers/developers involved are able to do something similar to VSD, supported by relatively simple exercises in the project, such as meetings with potential end-users and discussions with members of the Ethical Advisory Board of the project.

Persistence Surveillance of Difficult to Detect microdrones with L-band 3-D Holographic RadarTM[10]

This paper focusses on the detection of small, difficult to detect, microdrones and how to discriminate drones from other moving objects. Since scanning radars have to find a compromise between time on target and update rate, this can negatively impact the radar from reliably detecting very weak signatures targets in another clutter of objects. What this means is that the scanning radar cannot see a difference between drones and birds, when for example a drone is flying between a group of birds. Then employing a 2D antenna and appropriate signal processing to create a multibeam, 3D, wide area overcomes the weakness of scanning radars and achieves high detection sensitivity. A decision tree based classifier can be used to identify the difference between drones and other moving objects. Where it rejects non-drone targets, decreasing the number of false positives and increases true positives. Such that when neutralising such a moving object in the air, with high probability, it will be a drone instead of for example a flying bird.

Radar-Based Detection and Identification for Miniature Air Vehicles[11]

This paper discusses a radar-based detection and identification method for drones. More specifically the paper describes the design of a lightweight, X-Band (10.5GHz) radar system for use on a small-scale (less than 25 kg) rotorcraft. The prototype implementation of the radar is small enough to be carried by a drone and is able to differentiate other 'miniature rotorcrafts' (drones) by their doppler signature. The prototype uses a radar system which utilises electromagnetic energy to gain information on objects by analysing the reflected energy. The types of radars used are continuous wave radars, and a frequency modulated continuous wave radar and a Doppler radar. While in the paper the cause of the radar system is to avoid aerial collisions between uncrewed vehicles, it might still be useful to us as it is a method of detecting and identifying moving objects in the air. Therefore it this prototype can also be used/expanded for neutralising such aerial objects, might a drone be detected and identified.

Privacy, data protection and ethics for civilian drone practice: A survey of the industry, regulators and civil society organisations[12]

In this article, Finn and Wright present results of a survey of primarily European drone industry representatives, regulators, and civil society organisations that examined privacy, data protection, and ethics concerning civilian drone operations. The article also demonstrates, using self-reported information from industry representatives, that these stakeholders do not have a clear understanding of European privacy and data protection law. Finn and Wright argue that this can impact their levels of liability and protections for individuals on the ground. The findings in this article demonstrate that law enforcement, commercial, and private or recreational drone operators are all thought to be associated with significant privacy, data protection, and ethical risks. Here, the recreational operators are thought to carry the highest risks. The article concludes with a consideration of the implications of these findings for the regulation of privacy, data protection and ethics for civilian drone operations.

Robot ethics: Mapping the issues for a mechanised world[13]

In this article, Lin et al. describe what kind of new ethical and policy challenges are introduced to society due to the emerging technology of advanced robotics. They point towards the flourishing role of robots in society - from security to sex - and survey numerous ethical and social issues. These issues are divided into three categories; safety and errors, law and ethics, and social impact. Lin et al. argue that these future robotic technologies, first and foremost, need to be safe, while they point towards examples of where this went wrong in the past. They argue that with robotics, the safety issue is with their software and design. Errors and vulnerabilities are likely to exist. These errors and vulnerabilities could lead to fatal results when it comes to robotics. Furthermore, linked to the risk of robotic errors, it may be unclear who is responsible for any resulting harm. Product liability laws are primarily untested in robotics and, continue to evolve in a direction that releases manufacturers from responsibility, e.g., end-user license agreements in software.

It is argued that one way of minimising the risk of harm from robots is to program them to obey our laws or follow a code of ethics. That is, however, easier said than done as laws can be vague and context-sensitive. It is further argued that `even the three (or four) laws of robotics in Asimov's stories, as elegant and sufficient as they appear to be, create loopholes that result in harm'. The importance of privacy and laws concerning this privacy are touched upon. To make things worse, ethical and cultural norms, and therefore law, vary around the world, so it is unclear whose ethics and the law ought to be the standard when it comes to robotics. Such challenges could require international policies, treaties, and even laws. Other questions regarding the social impact are: `What is the predicted economic impact of robotics?', `How do we estimate the expected costs and benefits?', and `Are some jobs too important or too dangerous for machines to take over?'. The article presents many questions on which the answers can vary a lot. One thing the article makes clear, however, is that we have to start thinking about these challenges already.

Policing Police Robots[14]

Joh argues that as there will be changes in healthcare, manufacturing, and the military due to robots, these robots also have the potential to produce tremendous changes in policing. She argues that we can expect that at least some robots used by the police in the future will be artificially intelligent machines capable of using legitimate coercive force against human beings. She does not explicitly state whether she thinks this is a good thing or not. She continues by bringing up the assumption that police robots may decrease dangers for police officers by completely removing these officers from situations that have the potential to be dangerous. Moreover, those suspected of crimes may risk less injury if robots can assist the police in conducting safer detentions, arrests, and searches. On the flip side, however, the use of robots also introduces new questions and challenges about how democratic norms and laws should guide decisions made by the police. Joh argues that these questions have yet to be addressed systematically. Furthermore, she states that how we design and regulate some uses of police robots requires a regulatory agenda right now in order to address the foreseeable problems of the future.

Privacy and drones: Unmanned aerial vehicles[15]

In the paper, Cavoukian discusses, amongst other things, privacy concerns associated with the deployment of UAV technology. Furthermore, the paper addresses the privacy concerns by showing how privacy by design approach can assist in ensuring that the benefits of drones are facilitated while reducing privacy issues. Due to the manner in which drones may collect information, they pose privacy issues. The sensor equipment on board of drones may be commonplace in the consumer marketplace. However, drones have the ability to gather information dynamically from vantage points where for example regular video surveillance cameras or the camera of peoples phones could not reach. Since these drones can gather information so dynamically, on private property, for example, it creates these privacy concerns. Especially since the drone market is growing so much for the consumer market, now, if drones were to be designed with privacy in mind, the privacy concerns of the drone could be addressed appropriately. That is, drones should have privacy built into the system, the equipment on the drone should not monitor any private areas — for example, the insides of public washrooms, or peoples homes/backyards, and so forth.

Anti-drone flight protection systems and methods[16]

This patent, owned by Etak Systems LLC, a telecommunications company in the US, describes the user of Geo-fencing to avert uncrewed aerial vehicles. It describes the use of transmitting geo-fence coordinates, avoidance commands or disruption of radio communication in order to avoid UAV's entering no-fly zone. The patent describes various flow diagrams dictating how a UAV should receive, process and respond to avoidance commands transmitted over cellular networks, or between other UAVs. It assumes flowcharts for cooperating drones, where the main focus of the technology is collision and object avoidance, as well as procedures for the save removal of distressed (low battery, mechanically malfunctioning) or rogue UAVs. The following flowcharts consider mandatory "kill commands" the UAV is expected to follow, leading to a safe and immediate emergency landing, or, in the case of rogue drones, transmission of a signal interrupting the communication associated with the UAV.

Exploring civil drone accidents and incidents to help prevent potential air disasters[17]

Following an alleged drone collision with an Airbus A320 owned by British Airways at Heathrow Airport, the need to understand accidents and incidents involving drones arose. In this paper, Wild, Murray, and Baxter analyse and discuss one hundred and fifty-two events involving drones, or Remotely Piloted Aircraft Systems (RPAS). Differences were found between events involving these RPAS and events involving Commercial Air Transportation (CAT), where these events were categorised by their type, the specific safety issue, and the phase of flight. It was found that, compared to CAT, events involving RPAS more frequently involved a loss of control during flight, events occurring during takeoff, and general issues with the associated equipment. In the analysed events, technology factors, rather than human factors, contribute the most to these accidents and incidents involving RPAS. This article is part of our literature study as it provides more context on various events involving RPAS.

Determination and Evaluation of UAV Safety Objectives [18]

As the integration and acceptance of UAVs in society grows, so does the need for appropriate security measures when these UAVs carry out operations in civilian airspace. In this article, Clothier and Walker discuss the safety measures surrounding UAVs and the need for developers, operators, and regulators of UAVs to prove that they have at least the same level of safety standards as human-piloted aerial vehicles. The paper defines various safety objectives of UAVs, the impact of these safety objectives and their applications on the design and operation of UAVs, and the societal acceptance of the risk factors surrounding UAVs. It is of value to our research as it provides a base analysis of safety objectives of UAVs, and the findings of this work can be used to define appropriate countermeasures for (civilian operated) UAVs.

An innovative response to commercial UAV menace - Anti-UAV falconry [19]

This paper from the Educons University in Serbia talks about how UAV Falconry, i.e. the use of Birds like Eagles to attack undesired UAVs. It shows that the use of animals in security-related tasks has been done for thousands of years. Recently, the Dutch national police have partnered with private enterprises to train eagles to track and hunt down drones. The paper then discusses many drone-related incidents that would have been prevented by the use of this falconry. The enterprise responsible for training the eagles is Guard From Above, describes their method as “a low-tech solution for a high-tech problem”. The use of Eagles is pretty compelling due to their natural talent for mid-air combat, their massive speed advantage compared to drones and the ease of training. However, the solution was also criticised in the paper as being expensive, and limited to situations where birds could safely fly. The competition from other systems would deem this technology hard to justify in the future.

Taking Flight: The Future of Drones in the UK [20]

The UK is one of the countries at the forefront of the rapidly developing market of commercial UAVs. The public sector employs UAVs to significant effect, for example in emergency search and rescue operations, and assist people working in a hazardous sector to reduce the risk their job exposes them to. However, sparked by the recent disruptions of operation at Gatwick airport, among others, the government of the United Kingdom presented this document in January 2019 outlining the following regulations in the drone sector. Existing regulations prohibit drone use near people or property in the UK, as well as requiring the drones to follow a flight path where it stays within line of sight of the operator. The government of the UK outlines in more detail the following regulations, where they aim to work together with the Civil Aviation Authority (CAA) as well as drone manufacturers, in an attempt to ensure safety and security in the airspace while civil aircraft become more popular.

Defense against drones [21]

As a company specialising in X, Battelle has expertise in the areas of communications, electronic warfare and its countermeasures. They recognise that the growing popularity of UAVs poses real dangers to government and privately owned agencies, officials and assets. To serve the growing need for countermeasures against unwanted UAV presence, Battelle has created a focus area for counter unmanned aerial systems (cUAS). Their current top of the line product is aptly named the DroneDefender and disrupts the remote control systems and GPS systems of unwanted UAS. Their product presents one possible solution for the problem presented in our study and is therefore of great use to our work.

Counter-unmanned aerial vehicle system and method[22]

This patent, owned by Lockheed Martin Corp, an aerospace and defence company in the US, describes the use of nets to capture and eliminate uncrewed aerial vehicles. The patent shows a variety of methods that these nets can be deployed, from small nets attached to other UAVs to large parachute-like nets attached to larger UAVs or small aerocrafts. The patent also discusses the use of passive capturing methods, where a net is suspended from a parachute and deployed from a UAV, using trajectory calculations an enemy UAV could be captured from above.

Deterent for unmanned aerial systems[23]

This patent of a joint invention by three inventors describes an invention meant to fill the need for an integrated system and method of detecting, tracking, identifying and deterring the approach of unwanted UAVs. The patent further describes various systems, specifically for drone detection, classification, interdiction and countermeasures. It describes the differences between Human-in-the-loop (HIL) countermeasures and electronic countermeasures.

EU aviation agency publishes new drone framework[24]

This opinion from the European Union Aviation Safety Administration states their opinion on the widespread use of UAVs. They believe that the use of unmanned aircraft systems beyond the visual line of sight is of danger to airlines and other uses of airspace. Hence they propose that all hobbyists should register for an official flight plan in advance. The agency further wishes to distinguish two categories for drone usage, namely the open category covers drones of a mass between 250 grams and 25kg. Their maximum permitted EASA gives operating height as 120m or 394ft. They are free to be used as long as the vehicle remains in the line of sight. The principle behind specific, or specified, drone flights is that the operator must `declare' them in advance to a regulator. At the time of writing the opinion is still pending.

Gatwick spends 5 million pounds on anti-drone measures [25]

As a response to the drone incident in December 2018, Gatwick airport has decided to invest in the use of anti-drone measures. The airport has partnered with US airports to prepare against potential future attacks. Although the article does not show what exact instruments are to be used, it does show that the need for this technology is imminent. The article shows that anti-drone technology is now more critical than ever and companies like Gatwick airport are willing to invest a lot into current technology, as to avoid inconveniences to its passengers and the fines resulting from the 140000 stranded passengers.

Back to the root page.


  1. Yin, Tung. "Game of drones: defending against drone terrorism", Tex. A&M L, 2015. Retrieved on 2019-02-06.
  2. Nguyen, P., Ravindranatha, M., Nguyen, A., Han, R., & Vu, T. "Investigating Cost-effective RF-based Detection of Drones", ACM, June 2016. Retrieved on 2019-02-06.
  3. Revell, T. "Clash of the Drones", NewScientist, February 2018. Retrieved on 2019-02-07.
  4. UK Department for Transport, "Small Remotely Piloted Aircraft Systems (drones) Mid-Air Collision Study", July 2017, Retrieved on 2019-02-07.
  5. Civil Aviation Authority, "Drone Safety Risk: An assessment", January 2018,. Retrieved on 2019-02-07.
  6. Liberatore, S., "How do you catch a drone? With an even BIGGER drone and a giant net: Tokyo police reveal bizarre 'UAV catcher'", DailyMail, December 2015, Retrieved on 2019-02-07.
  7. Burns, M., "The SkyWall 100 bazooka captures drones with a giant net"], TechCrunch, 2016, Retrieved on 2019-02-07.
  8. Royakkers, L. M. M., & Est, van, Q. C. (2015). A literature review on new robotics: automation from love to war.International Journal of Social Robotics, 7(5), 549-570. DOI: 10.1007/s12369-015-0295-x
  9. Royakkers, L. M. M., & Steen, M. (2017). Developing tools to counteract and prevent suicide bomber incidents:A case study in Value Sensitive Design. Science and Engineering Ethics, 23(4), 1041-1058. DOI:10.1007/s11948-016-9832-8
  10. Jahangir, M., & Baker, C. "Persistence Surveillance of Difficult to Detect microdrones with L-band 3-D Holographic RadarTM", Sensor Signal Processing for Defence (SSPD), September 2016. Retrieved on 2019-02-07.
  11. Moses, A., Rutherford, M. J., & Valavanis, K. P "Radar-Based Detection and Identification for Miniature Air Vehicles", Control Applications (CCA), September 2011. Retrieved on 2019-02-07.
  12. Finn, R. L., & Wright, D. (2016). Privacy, data protection and ethics for civilian drone practice: A survey of industry, regulators and civil society organisations. Computer Law & Security Review, 32(4), 577-586.
  13. Lin, P., Abney, K., & Bekey, G. (2011). Robot ethics: Mapping the issues for a mechanised world. Artificial Intelligence, 175(5-6), 942-949.
  14. Joh, E. E. (2016). Policing police robots. UCLA L. Rev. Discourse, 64, 516.
  15. Cavoukian, A."Privacy and drones: Unmanned aerial vehicles", Ontario: Information and Privacy Commissioner of Ontario, Canada, 2012. Retrieved on 2019-02-07.
  16. Etak Systems LLC."Anti-drone flight protection systems and methods", Google patents, 2016. Retrieved on 2019-02-07.
  17. Wild, G., Murray, J. and Baxter, G."Exploring Civil Drone Accidents and Incidents to Help Prevent Potential Air Disasters", Aerospace, 2016. Retrieved on 2019-02-08.
  18. Clothier, R., Walker, R."Determination and Evaluation of UAV Safety Objectives", Queensland University of Technology, 2006. Retrieved on 2019-02-08.
  19. Slavimir S. Nikolić "An innovative response to commercial UAV menace - Anti-UAV falconry", Educons University, 2017. Retrieved on 2019-02-09.
  20. Secretary of State for Transport, UK "Taking Flight: The Future of Drones in the UK", UK Secretary of State for Transport, 2019. Retrieved on 2019-02-09.
  21. "Battelle defense against drones", Battelle Memorial Institute, 2019. Retrieved on 2019-02-09.
  22. Lockheed Martin Corp."Counter-unmanned aerial vehicle system and method", Google patents, 2016. Retrieved on 2019-02-10.
  23. Parker, D., Stern, D., Pierce, L."Deterent for unmanned aerial systems", Google patents, 2016. Retrieved on 2019-02-10.
  24. [1], EASA, 2018. Retrieved on 2019-02-10.
  25. "Gatwick spends £5m on airport anti-drone measures", The Financial Times, 2019. Retrieved on 2019-02-10.