# Group members

Name Student ID Major
Jort de Bokx 1050214 Software Science
Sander de Bruin 1006147 Software Science
Stijn Derks 1008002 Software Science
Martin de Quincey 1007047 Software Science and Applied Mathematics
Nick van de Waterlaat 1009357 Software Science

# Introduction

The goal of this wiki page is to show a study and analysis of a robotic subject. This research is an assignment of the course Robots Everywhere (0LAUK0). For this project, students work in a group of five people choosing a subject in the core of robotics to work on, thereby making sure the USE aspects are leading. As is usual in a Wiki, multiple pages will be used rather than considering one extremely long page. Make sure to explore all subpages contained under this page.

# Initial ideas

In this section, we present some initial ideas that were formed at the start of the project. Each of the initial ideas includes a short description of the problem related to the idea. Ultimately, the chosen idea is given.

## Robotic surgery

With all the progress in robotics, we have now reached a stage in time where it is (almost) possible to let robots do surgery. There have been quite some recent breakthroughs, and it is also already applied to some scale in hospitals. However, there are some aspects to this robotic technology that need closer investigation.

## Medical rehabilitation with the help of robots

Many people suffer from injuries that may require long-term medical rehabilitation. This rehabilitation is typically complex and takes a lot of staff to help guide the patients through the process. Then there might be benefits for both the patients and the staff helping the patients with rehabilitation if robotics were to help the rehabilitation process.

## Drone interception

Between 19 and 21 December 2018, hundreds of flights were cancelled at Gatwick Airport, following reports of drone sightings close to the runway. The airport did not have any measures to prevent this issue. Many users of airlines were stranded, and airlines (enterprises) lost. The airport only had detection and tracking devices, but no counter-drone mechanism. Just like birds, drones can cause enormous damage to aeroplane engines and are therefore illegal around airports. However, no airport yet has a fully working anti-drone defence mechanism, while most airports do have anti-bird systems, consisting of noise mechanisms to scare birds away.

## Drone pesticides

An important consequence of the increased global population is the demand for food. In order to meet these demands, farmers require the use of pesticides to ensure enough yield from their crops. However, the overuse of pesticides and fertiliser can have huge negative impacts on society. Hence we the use of drones to analyse the state of farmland and automatically apply fertiliser and pesticides as needed could make a farmer’s job easier, making the production more eco-friendly.

Trading bots have been used on the stock market for quite some time already, but ever after the boom of cryptocurrencies, the usage of these bots has become ever more increasing. The stakeholders of these bots are people that are active in, for example, the stock market and cryptocurrency market. People could use such a bot in order to achieve a passive income. Designing such a bot for interested parties would be interesting. Furthermore, it would be interesting to consider the ethical discussion regarding the permission to use such trading bots in the stock market.

## Networking AI

Gridlock is problematic in large western cities, but also many large cities with underdeveloped infrastructure in countries like Asia. It massively hinders any form of transport, and also unnecessarily increases pollution. Forms of AI in private cars or forms of public transport such as buses or trains might help reduce this problem. On an abstract level, buses or trains could adjust their schedule or route such that they are deployed at places where passengers are waiting in real time, not where they are expected to be waiting. This way, one might prevent the case where two half-full buses are driving on similar routes. By sharing information and adapting to real-time information, in this case only one bus would be necessary.

## Use drones to monitor and improve marine life

Due to climate change, many problems arise. A large part of these problems emerges in the seas and underwater. Examples include changes to the habitat of marine mammals, irreversible damage to coral reefs, and already endangered species being threatened quicker by their changing environment. Current use for them is flying through and capturing fluid samples of the exhaled fluids of whales, in order to monitor their health. Specific autonomous robots designed for underwater operation might help monitor the state of coral reefs, and introduce new coral to a reef to support its growth.

## Chosen concept

The concept we have chosen considers Drone interception but applied in the setting of airports. Initially, we consider this concept in a more general context, but after the feedback provided by the professors and internal discussion, the group has decided to limit itself to the context of airports.

# Project setup

In this section, we put the project setup under a microscope. We take a look at the objectives of the project; the approach is taken, the planning during the project, milestones of the project, and deliverables that will exist at the end of the project.

## Objectives

The objective of our project is designing a decision model for airports to decide what anti-drone solution is the best. This model will be delivered by means of a report that can indicate which solutions are better for which types of airports. This report will also give extensive argumentation for why certain solutions outperform others in certain scenarios.

Objectives of the project as a whole include:

• Gaining insight into accidents and incidents involving various forms of drones.
• Identify and specify the currently existing countermeasures and counter mechanisms against drones and UAVs in general.
• Identify and specify the USE stakeholders of the problem space and their interests regarding possible solutions.
• Propose multiple possible solutions to the problem.
• Identify the advantages and the disadvantages centred around user interests for each provided solution.
• Validate and verify that our proposed solutions solve the discussed problems with respect to the USE stakeholders and their interests.
• Design a basic decision model around providing solutions for airports against UAVs.

## Approach

We now take a look at how we will approach this project. We will start our approach by doing an extensive study into the current state of the problem. We will do this by studying the literature of different forms. We will look at papers where this problem has been discussed before, but also at what the current solutions are at the moment and what their flaws are. Furthermore, we also look at studies and research of institutes that have made investigations into this phenomenon.

After we as a group have a good grasp on the problem, we analyse the problem ourselves from a USE (User, Society, Enterprise) point of view. These three components will be central in our study, and the development of our design as the users of the technology always need to be the main focus. Following this study into the USE aspects surrounding our problem space, we expect different categories of subproblems to arise. For example, when considering two distinct incidents involving UAVs, they might be categorised by the type of failure that occurred, be it a human failure or technical failure. We expect that many of these distinctions can be made, and as different categories of subproblem might involve different USE aspects, they might require different solutions. Furthermore, we take a look at different types of airports and see what each of these types need for an anti-drone solution.

After this, we will provide possible solutions for a number of distinct problem categories. For each discussed problem category, we will then present multiple implementations of these requirements and functionalities, which will be our first drafts. These draft solutions will be further discussed and analysed based on their advantages and disadvantages. We will also provide research into the feasibility of these proposed solutions.

As the discussed subproblems heavily integrate with various aspects of society, we are also interested in the ethical aspects of the evolution of the proposed technologies of counter-drones. We will investigate the ethical and regulatory consequences of these developments. We might also provide insight into which areas of the problem space have not been sufficiently discussed by previous research and falls outside the scope of ours. For future reference, we also look ahead and shortly discuss improvements or otherwise changes to our proposed solutions, that are not currently possible due to technical or other limitations. Finally, we will wrap up with completing the wiki and our documentation of the project.

Once we have a good comparison fo the various existing solutions, we will implement them in a concise decision model, aimed at informing Airports of the status quo regarding drone defences, and provide a decision model to allow them to choose the most suitable option for them. The model will be presented through the means of a Web Application.

## Planning

We now take a look at the planning of the project. The planning is presented in the form of an excel sheet that clearly states the tasks that need to be carried out, by whom these tasks will be carried out, an estimation of the time that it takes to carry this task out, if the task has been completed or not, and when it needs to be completed. Furthermore, an orange cell indicates that this will be done during a group meeting, and a blue cell indicates that this will be done outside of a meeting. Note that this planning also considers the division of work in no small degree.

## Milestones

We now consider the milestones within the project. Here, we consider Table 1 that displays the accomplishments on a specific date. Furthermore, if there were any learning moments during each of these accomplishments, they will be written down in the Aditional notes' column and taken into consideration for the next accomplishment. Note that this table will be regularly updated throughout the course.

Table 1: Milestones
Date Accomplishment
06/02/2019 Finalise the decision of the subject
17/02/2019 Finalise research into State of The Art
19/02/2019 Formulate analysis of problem space
6/03/2019 Formulate possible solutions to identified problems
27/03/2019 Formulate possible further improvements
29/03/2019 Formulate conclusions regarding proposed solutions
26/03/2019 Create a presentation format of our research
01/04/2019 Present complete research
05/04/2019 Finalise the Wiki and documentation

## Deliverables

We now cover the deliverables of this project. The deliverables focus on the problem introduced in the problem description. These deliverables for this project will be as follows: In this section, we refer to the present situation, which consider the present situation regarding the specific problem description. We discuss the current rules and regulations, current solutions, and the limitations of the current rules, regulations, and limitations.

• A presentation regarding the problem and possible solutions

This presentation will be held in the final week of the course. In this presentation, we start by introducing a problem through a summary of the problem description. Then, the finding regarding the problem will be presented. This is followed by multiple solutions to the problem with their advantages and disadvantages. Then, we zoom into the best' solution and provide a design regarding this solution. If possible, a demonstration will also be given.

• A literature study in the form of coherent Wiki pages in a hierarchical manner

This Wiki page contains an in-depth study regarding the problem introduced in the problem description. An extensive literature study will be presented, which offers multiple solutions with both their advantages and disadvantages. Furthermore, it will be argued that what solution would be the best' through means of a decision model. This is followed by areas that are still undiscovered and improvements that can be made to our design.

• A Web App that implements a decision model

This Web app should implement a form of a decision model. The result of this decision model should be a possible solution against unwanted UAVs near airports based on input obtained from an individual. This input should consider the needs, beliefs, and wants of an airport when it comes to defending themselves against illegal UAV activity.

# General problem

## General problem description

Between 19 and 21 December 2018, hundreds of flights were cancelled at Gatwick Airport, following reports of drone sightings close to the runway[1]. A total of 760 flights were disrupted on the 20th of December due to the drone. Naturally, this angered many people whose flight was delayed. Not only does it anger people, but it is also a financial worry for the airport organisation as all of these people with delayed flights have to be compensated. The airport did not have any good' measures to prevent this issue. Gatwick chief operating officer Chris Woodroofe said: The police are looking for the operator and that is the way to disable the drone'[1]. Woodroofe further elaborates that the police had not wanted to shoot the devices down because of the risk from stray bullets. This is, of course, not something that is to be repeated as this caused much inconvenience for many travellers. The airport itself only had detection and tracking devices, but no real effective counter mechanisms available. This issue is not limited to the setting of airports, but it can be further extended to any hot spot, such as the centre of cities, special events that involve essential figures, and more. With the ever-increasing possibilities of technology, it should in the future not be unexpected for an unmanned aerial vehicle (UAV) to suddenly show up and wreak havoc. This havoc can range from taking pictures of people in public places to spy or stalk them to terrorists that use UAVs to drop bombs in highly populated areas. These occurrences are more likely to appear as the technology we possess increases.

We think that we should not sit idle and passively wait for the worst-case scenarios to occur before starting to think about countermeasures. The recent incident between 19 and 21 December 2018 at Gatwick Airport should already sound an alarm that we should take an active attitude and develop mechanisms that counter UAVs in productive ways. These mechanisms should be able to deal with much more than mere birds and should consider any form of terrorism that can be caused through the airspace.

## State of the Art

In order to gain more insights regarding the topic, we do extensive research. The results of this research can be found on the State of the Art page.

## General USE aspects

In this section, we consider the users, society, and the enterprise based on the general problem description.

### Users

There are multiple stakeholders involved in a solution to the problem introduced in the problem description. By far the largest and most diverse category of stakeholders consists of those parties that are (majorly) disadvantaged by unauthorised or unwanted UAV operations, or malicious events that could follow. We can identify several subcategories of stakeholders whose material possessions or immaterial values are at stake.

The most important users are as follows:

• The Government

As the governing body, a collection of many large instances with national interests, the government of a nation aims to preserve the material and immaterial assets of its citizens. This goal might be obstructed by the unwanted presence of UAVs or events caused by them.

• Non-governmental organisations

Includes companies or other privately owned bodies that want to protect their material assets against damage from UAV incidents, or protect immaterial assets such as privacy or intellectual property that could be violated by the unwanted presence of UAVs.

• Civilians or individuals in general

Civilians or individuals, in general, are also stakeholders in the problem space that we consider. They might have their assets violated in some way by UAVs or UAV related events, such as civilian espionage empowered by UAVs. Since drone flight is growing as a commercial pass-time, more specifically the operation of drones by civilians for fun is becoming more popular, this user group must also be considered as a stakeholder from this perspective.

### Society

Society as a whole is affected by the already existing and upcoming dangers of drones. First of all, drones can be a massive hindrance at for example airports (Gatwick airport), football stadiums or other public places. However, apart from simple hindrance, drones can also be extremely dangerous for society, as they can be weaponised and used by terrorists, the military or any other person with bad intentions. Furthermore, more and more people are using drones privately, causing privacy issues for society, as these drones are equipped with a camera most of the times and can easily reach private places. This is why drone interception is so vital to society. If there were to be a tool that could detect, identify and neutralise drones, this could help in a decrease of hostile drones and thereby also decrease the dangers above that drones bring to society.

### Enterprise

Enterprise is greatly affected by the illegal use of drones; for example, the airlines at Gatwick lost much revenue due to delayed flights and passenger compensation. The airport itself also suffered from the forced shutdown. Drones also threaten other industries, espionage via drones can be done remotely, where attackers may steal a company secrets through aerial photography or by taking pictures through windows. Hence the development of anti-drone will be of enormous benefit to existing enterprises but also spark new business opportunities for security contractors and UAV oriented startups.

## Zoom in

After a lot of internal discussions, we found out that we have to zoom in more due to otherwise undertaking too broad of a problem space. Therefore, we zoom into the problem description and define a more specific problem description on the Specific problem description page.

# 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[2]

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[3]

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.

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[5] 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[6] 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' [7] 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[8] 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[9] 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[10] 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[11] 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[12] 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[13] 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[14] 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[15] 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[16] 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[17] 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[18] 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 [19] 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 [20] 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 [21] 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 [22] 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[23] 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[24] 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[25] 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 [26] 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. # Specific problem In this section, we elaborate on the specific problem we want to consider. Comparing the specific problem to the general problem, the specific problem considers a particular context and environment. This was done in order to limit the scope of the problem. ## Specific problem description As described in the Approach' Section, we expected the societal issue of unwanted UAV presence to be divisible into multiple subcategories. Following our initial literature study, we indeed found this to be the case. There are many axes along which the problem space can be divided. For example, we might consider a division based on the nature of the cause of a drone incident, and as such whether it was caused by human failure or technical failure. Another possible distinction can be given based on the specific part of society that is impacted, whether it be the privacy of individuals when a camera-equipped UAV flies over their backyard, or the safety of a group of users when there are UAVs present around an airfield. When we consider the existing legal regulations, another commonly occurring division is that between human-controlled and autonomous UAVs. This realisation leads us to formulate a more specific problem definition with a smaller scope. In our study, we consider possible deterrents against unwanted UAV presence around airports. This includes studying the current legal regulations considering UAVs, both in general and more explicitly considering airports. The term UAV is also divisible into multiple subcategories; for this study, we take all sub-types of UAV into account. These specific sub-types will be further discussed in the following Section. As can be observed in the image below, the number of drone-related incidents has risen dramatically over the last few years. The reason for this is that technology and its evolution moves faster than regulators, whose job is to maintain safety standard when confronted with ever-evolving aspects of technology. Regulations require extensive research into the technology it should apply to, and these regulations also take time to roll out. In the meantime, the technology in question does not stop evolving and by the time regulations take effect, the technology in question has often already evolved beyond the scope of the regulations. Different categories of drones, which will be further discussed later, pose different threats to aeroplanes. One might hit the windscreen of an aeroplane, posing a direct danger to the pilots and therefore the plane's passengers, or a drone might get sucked into the air stream entering the plane's engines and ultimately destroy a turbojet motor propelling the plane. Figure 1. Airprox reports involving drones and other objects. Because different types of drones and different types of airports exist, there are multiple types of incidents to consider. All of these are factors that should be taken into consideration when deciding which drone countermeasure should be applied in a particular situation. This means that anyone drone countermeasure is doubtful to work in a majority of situations, and care should be taken when choosing which countermeasure to invest in. A 'geo-fencing' system, which prevents commercial drones from entering certain no-fly zones, might be bypassed or disabled, not correctly implemented by the third party drone manufacturer, or include a multitude of other problems. A drone that launches a net to disable other drones might be difficult to operate and has many downtimes after it fails to take out another drone. When the safety standard is high, the ones at airports are exceptionally so; this becomes a difficult problem. It is not a simple decision to choose which drone countermeasure should be applied. ## Examples of financial consequences It is essential to consider the financial consequences of the problems proposed in the specific problem description. Let us review a recent example that sparked the controversy regarding drone interception even more. The drone activity that obstructed flights in and out of London’s Gatwick airport for 33 hours cost airlines an estimated £50 million ($64.5 million)[27]. This estimate of £50 million is based on EasyJet’s disclosure that it lost £15 million ($19.3 million) in revenue and customer welfare combined during the 33 hours long illegal drone activity. Easyjet further stated that the drone incident was a wake-up call for airports. Not only Gatwick but also other airports are now plotting to try to enhance its response to any similar threats that may occur in the future. Gatwick’s flight interruptions affected about 140,000 people, where 82,000 of them were EasyJet customers. In July 2017, Dubai International Airport was shut down temporarily due to illegal drone activity. The costs of the shutdown were roughly$100,000 a minute according to Emirates Authority for Standardisation and Metrology (ESMA) estimates[28]. ESMA has introduced new regulatory standards for commercial and recreational use of drones, which includes a monitoring system for detecting UAVs in the country. In 2017, the Dubai Civil Aviation Authority (DCAA) head of airspace safety, Michael Rudolph, told Arabian Business that they were planning on testing their indigenously developed spectrum analysis technology to track threats of rogue drones and pinpoint their locations. With this, it would be possible to attack the rogue drones. In Dubai, it is now obligatory for all drone operators to apply for a license and undergo a training program. Since the illegal drone incidents, several new no-fly zones have been introduced by the General Civil Aviation Authority.

In January 2019, Heathrow Airport had closed its runway after a possible drone sighting. This happened three weeks after the Gatwick fiasco, in which the airport was closed for 36 hours after multiple drone sightings had occurred. Around 140,000 travellers were impacted after 1,000 flights were cancelled or diverted. No numbers regarding the costs have been given, but we can only assume that these costs were relatively high but not as high as the estimated cost of Gatwick's incident. All in all, these are just a few examples of how tremendous the financial consequences of illegal drone activity around airports can be.

## State of the Art

Again, in order to gain more insights regarding the specific problem, we add additional information to the State of the Art that was started for the general problem description. We further build upon it in this section.

## Specific USE aspects

In this section, we consider the users, society, and enterprise when considering the specific problem description.

### Users

When we take a look at the users in the more specific context of considering solutions against unwanted UAVs at and around airports, we see a shift in the types of users compared to the previously defined users in the more general setting. We see that mainly non-governmental organisations such as airports and airlines are the users of this more specific setting instead of the government, which was one of the users in our general setting. These types of users are also part of the use aspect enterprise' and will be elaborated on in more detail in the corresponding section below. Indirectly, also passengers of flights are users of solutions against unwanted UAVs at and around airports, as passengers benefit from such solutions since they just want to be able to travel without any hindrance. Again passengers of flights is a type of users that overlaps with the use aspect 'society' and will be elaborated on in more detail in the section below. Lastly, companies with the intent/goal to intercept or detect flying objects such as UAVs are, to some extent, users of solutions against unwanted UAVs.

### Society

Let us take a closer look at how this specific problem description is relevant when we consider a society concerning airports. If a UAVs enter the air space of an airport, aeroplanes are not allowed to land at the airport nor are they allowed to leave the airport. Therefore, airports have placed a ban on the usage of UAVs around the airport in order to make sure that aeroplanes can still land and leave the airport. As one might already know, a tremendous number of people visit airports every day. In 2017, Schiphol airport, located in Amsterdam, already counted 68 515 425 passengers[29]. One can already imagine how enormous the consequences can be if this airport cannot be used for a few days. This means that if a UAVs flies by for whatever reason, a large number of people will not be able to travel. This results not only in many angry travellers but also in airport companies that have to compensate these travellers for the delays introduced by these UAVs.

From a societal perspective, this would mean that all travellers have a risk of their flight being delayed, which is undesirable due to many reasons as elaborated on previously. As of now, we have only considered the situation where a UAV simply flies by but what if this UAV has malicious intentions. For example, what if this UAV has been weaponised and is used by terrorists or a specific individual with malicious intentions and is used to wreak havoc at the airport. Then, these weaponised UAVs could be extremely dangerous as they could result in mass-killings. This would be a colossal disaster, and this should be avoided at all cost. A disaster is not only bound to happen when we consider weaponised UAVs. A disaster could also occur when the systems of the airport do not detect one of these UAVs. This UAV could then end up damaging the aeroplane, which could result in perilous situations. For example, we can expect disastrous situations when a UAV gets stuck in the motor of an aeroplane. All things considered, UAVs cannot only be hazardous to society when operated by malicious attackers, but they can also introduce many annoyances.

### Enterprise

When we restrict the USE case analysis to only deterrents against unwanted UAVs or drones around airports, the enterprise aspect of the use analysis becomes more concrete. The main type of enterprise that is under risk is the airport branch. The total revenue of the aviation industry in 2018 alone is a staggering 821 billion USD[30], so there are huge amounts of money at risk here. The current protocol is to suspend all flights of the airport by 30 minutes, the average lifespan of a drone. This means that, should drones occur often enough, all flights will be suspended for an indefinite amount of time[31]. This will, of course, have huge costs for multiple branches of the aviation industry. The three most notable branches in our opinion are the airports, the airlines and the companies who use aviation to transport goods. For these three enterprise branches, we will analyse the consequences of such an unwanted drone near an airport.

#### Airports

Airports suffer the largest loss in the case of such a drone in the airspace, which makes sense since it is where the problem is located. The airports suffer huge financial losses mainly through three different ways. First and foremost, no profits can be made when no planes fly. For example, the drone incident at Gatwick Airport caused a loss of over 50 million English Pounds[32]. This was caused by suspending all flights, which were just over 400, over the total duration of 33 hours. The airport suffers a huge blow to their reputation. So the hourly financial losses are huge for airports when flights must be suspended due to drones in the area. Furthermore, should one airport consistently suffer from the presence of unwanted drones, both airlines and travellers might opt to choose a different airport. The other airport might be farther away, but it will be a more reliable airport. This would result in a drop in total passengers at the airport.

#### Airlines

Airlines such as RyanAir, KLM or EasyJet also suffer huge losses during the event of a drone suspending or cancelling flights. The airlines are the companies actually offering flights to travellers. What also causes more losses for airlines is that they have to compensate the travellers for the delay or cancellation of their flights. By European Law, airlines are required to provide travellers with enough food, drinks, and nightly accommodations for as long as necessary[33]. For a long, sudden suspension of flights at one place, which is the case in our problem, this also becomes an enormously difficult task for an airline. If the airline would not act accordingly, the airline could also suffer from a huge reputation loss, resulting in travellers not flying with that airline anymore. Furthermore, the travellers are also eligible for financial compensation by European Law[33]. Airports.

Another aspect of this branch are the employees of the airlines. Apart from the company as a whole, the employees, such as flight attendants and pilots, suffer significantly from such an airline 'shutdown'. This is because of the way that the employees get paid. They do get a baseline salary, but the most salary they receive come from the hours that they are actually in the plane either flying or aiding passengers[34]. If the planes do not fly, they suffer from a huge salary cut, which means that the whole branch of airline employees have financial losses.

#### Companies who transport goods via aviation

Another enterprise that suffers from delaying and cancelling of flights at an airport are transport companies. In general, these goods are transported with different aeroplanes than passenger aeroplanes, but cargo is usually transported with passengers in the same aeroplane [35]. Besides, cargo aeroplanes also frequently fly to airports just for packages, since restaurants, shops, e.g. are not necessary there, decreasing airport costs. However, these airports can also be subjected to an unwanted drone in the airspace. Again, the protocol is that the aeroplane will not land and thus will be either delayed or cancelled. This can have dire consequences for such companies. The delay of their goods usually set off a chain reaction of consequent delays, which can be devastating if the timing is crucial. In conclusion, the consequence of these delays for these companies is huge financial losses and huge logistic issues to fix the delays of their goods.

# Present situation

In this section, we consider the present situation regarding the specific problem description. We interview an airport and look at current solutions.

## Airport Interview

In order to get a more unobstructed view of the issues our users (airports) face today we decided to ask them a couple of questions. We want to obtain a clear picture of their current approach to airport security regarding drones, what the consequences would be if a drone were to fly in their airspace right now, and what the consequences were of the 19th of December Gatwick incident. We will then ask them what their requirements would be for a drone defence mechanism.

• What is the airport's current mechanism for detecting drones?
• How will the airport respond when the drone is sighted in restricted aerospace?
• Roughly how much damage will the airport take if a drone were to restrict air traffic for 1 hour?
• The 19th of December and 21st of December drone attack at Gatwick airport caused over 1000 flights to be affected, did your airport get affected by the knock-on effects?
• What would be the maximum budget for an automated anti-drone mechanism?
• What kind of system would you imagine when thinking of anti-drone mechanisms?

We contacted most major Dutch airfields; Eindhoven, Schiphol, Maastricht Aaken, Groningen, Twente, Den Helder, Rotterdam the Hague and Bergen op Zoom.

Eindhoven airport responded to the questions, firstly stating that Eindhoven airport uses the runway and infrastructure provided by the Military airbase Eindhoven. This means that the Dutch Royal Airforce is responsible for air traffic control and hence the safety in the airport's airspace. We had the following answers to the aforementioned questions:

What is the airport's current mechanism for detecting drones?

At the moment the airport has no automated system to detect drones. At the moment this done by sight from the air traffic control tower.

How will the airport respond when the drone is sighted in restricted aerospace?

This depends on the location of the drone. At the moment an incident affecting air traffic has not yet occurred. When a drone is spotted, we will suspend all traffic.

Roughly how much damage will the airport take if a drone were to restrict air traffic for 1 hour?

I cannot answer this question [in detail], for the military activities, the impact will be limited. However, the impact on Eindhoven Airport will be much more significant.

The 19th of December and 21st of December drone attack at Gatwick airport caused over 1000 flights to be affected, did your airport get affected by the knock-on effects?

We were not affected as there are no flights to Gatwick from Eindhoven.

What would be the maximum budget for an automated anti-drone mechanism?

None, for safety there will always be a budget available.

What kind of system would you imagine when thinking of anti-drone mechanisms?

The location, altitude and flight-profile are crucial. The weight of a drone is also very important.

The correspondent also told us he was very interested in our research, offering the opportunity for further collaboration.

## Solutions

In this section, we will take a look at solutions against unwanted UAVs at and around airports that are currently/in the near future being used by airports/authorities. These solutions might exclude many solutions that might be useful but are simply not in use due to for example the jurisdiction not being up to date with the current technology. However, a list of all possible solutions including solutions that might not even be feasible right now, but maybe within the next few years will be discussed in the section solutions. It is important to note that there are different rules for different types of drones.

• There will be European rules and regulations in the near future, expected around June 2019, obligating operators wanting to fly with a drone that is heavier than 250 gram to be registered. Drones will be obligated to send out identification signals such that authorities, for example, the police, can trace and identify the operator of the drone[36].
• With these same rules and regulations drones will be obliged to be equipped with geofencing software. This will restrict the operator to be able to fly close to an airport[36].
• Anti-drone systems deployed at two London airports are capable of tracking the devices from as far as six miles away. As well as being able to sever communications with the operator, some models can also destroy the drones using a laser beam. However, it is not exactly been released to the public as to what equipment is used and how it works[37].
• The police trains eagles to make them consider unwanted UAVs as preys, such that they would catch the UAVs and place them in a safe area. However, the Dutch police have already stopped using this solution because training the eagles is more expensive and complicated than they anticipated[38].
• In May of 2018, London Southend Airport successfully tested an anti-drone system that combines optical sensor and radio frequency to detect drones[39].
• The US Federal Aviation Authority trialled the Anti-UAV Defense System (Auds) system in 2016. It uses high powered radio waves to disable drones, it blocks their communication with the controller and switches them off mid-air[39].

## Limitations

### The jurisdiction regarding drones is not up to date with current technology

As is often the case, the laws we have are not able to keep up with the tremendous advancements of technology [40]. This has happened many times already in history, for example with the rise of copyright laws at the end of the 19th century. Due to the huge advancements in copying and spreading literature, originals authors lost lots of money to people selling the author's work without proper permission. This was facilitated due to the rise in printing technologies. Under the pressure of this growing technology, the copyright laws had been created, albeit years and years later after the problem had occurred [41]. This example is just one of the many examples where the laws come much too late after the technology has been fully developed.

The same problem is currently happening to drone regulations. Over the last decade, the technological advancements in drones have been enormous, and as a consequence, the accessibility of drones for normal people has increased as well. Nowadays, anyone can buy a drone without any license and fly the drone with a camera to any house in his or her neighbourhood for under 100€ [42]. This seems like an obvious illegal intrusion of privacy by laws such as personality rights ("portretrecht"). However, these rules are not properly enforced concerning drones. In Europe, new drone regulations will be enforced, starting halfway through the year [43]. However, there have been huge debates about how the regulations should be changed, with no concrete answers. Just recently, on January 21 2019, the Dutch House of Representatives ("Tweede Kamer") organised a "rondetafelgesprek", where experts discussed what should be done in terms of regulations[44]. These examples show that the regulations of drones are not up to date with the current technological advances of drones.

### Limitation of current solutions

As we have described before, current solutions such as the eagle experiment, are simply not good enough to efficiently provide a solution to the problem. For this exact reason, airports and governments all over the world are investing vast amounts of money in the development of technologies to counter drones. Heathrow and Gatwick airport are two examples of airports that are investing millions of dollars in this technology [37].

Apart from the fact that some solutions simply do not work, other proposed solutions have negative side results. For example, shutting the unwanted UAVs down with radiowaves means that they will crash straight down to the ground. If such a drone falls on someone's head, he or she could get seriously injured. Furthermore, the crashing drone can also break specific equipment when falling. Lastly, if the drone, e.g. falls and breaks on the runway, this could also be dangerous. These consequences also apply to the current solution where the drones are shot down with a laser for example.

Other solutions such as geofencing and identification signals also have the flaw that they can be bypassed easily. If someone intentionally wants to fly a drone to the airport, it is not that difficult to make sure that the drone does not broadcast identification signals anymore. The drone operator could also make sure that the drone does not send signals that the geofencing uses, such that the geofence is, in fact, useless for deterring this drone. Furthermore, someone could also build a drone themselves, and choose not to send these required signals. This would indeed be against the law shortly, but since the drone operator is already engaged in criminal activities, these regulations would most likely not stop him. Thus, the technologies can easily be bypassed, rendering them as useless.

# Drones

## Introduction

There exist various categories of drones. For example, not only small drones for recreational use exist but also large weaponised drones. It is important to categorise the various types of drones that exist in order to deal with each category appropriately. Furthermore, the current rules and regulations when it comes to commercial and recreational use of drones are essential to consider as well. We do this in order to get a better understanding of what is allowed and what is not allowed. This better understanding will make it easier to provide solutions for the various categories of drones and their usage.

## Current regulation

When considering the current rules and regulations, we do not merely restrict ourselves to the rules and regulations surrounding airports, but we increase the width of our view to a more general perspective as we think we might do interesting findings this way. Different countries have different rules and regulations when it comes to UAVs. Furthermore, distinctions are made between recreational use and commercial use. The United States of America (U.S.A.), for example, considers different rules when it comes to recreational use and commercial use. The requirements when flying a drone under commercial use are much stricter than flying a drone under recreational use. If one wants to fly under commercial use, one has to pass an FAA test and receive Part 107[45] certification. Furthermore, a drone needs to be registered so that the owner of the drone can be traced back in case this is needed.

A few guidelines to follow when flying a drone in the U.S.A are as follows[46]:

• Fly at or below 400 feet
• Keep your drone within sight
• Never fly near other aircraft, especially near airports
• Never fly over groups of people
• Never fly over stadiums or sports events
• Never fly near emergency response efforts such as fires
• Never fly under the influence
• Be aware of airspace requirements

There exist applications, available for smartphones and on the web, that display where a drone is allowed to fly. One example is AirMap that shows users that they should be at least five miles away from an airport to operate the drone without notifying the control tower of the airport. As you might have realised by now, the rules and regulations regarding drones are still a work in progress. As the rules and regulations per country differ significantly, we will solely focus on the rules and regulations considered in the Netherlands. This is only natural as the project is carried out in the Netherlands as well. The Netherlands considers different rules and regulations based on the type of usage of the drone. The main categories specified by the Dutch Government consider recreational use and commercial use.

### Recreational use

When one flies a drone for personal purposes, one must abide by the Model Aeroplanes Regulations[47]. This means that one is not permitted to fly over groups of people or connected buildings. Furthermore, the drone needs to be in sight at all times. As soon as one sees an aeroplane or helicopter approaching, one must land as quickly as possible.

For reasons of safety, it is not allowed to fly a drone just anywhere. As mentioned earlier, it is not allowed to fly over groups of people. The Dutch Government has also set down requirements regarding the conditions under which it is allowed to fly[48]. This includes but is not limited to:

• You must be able to see the drone at all times.
• You may not fly in the dark.
• You must always give priority to all other aircraft, such as aeroplanes, helicopters, gliders, et cetera. This means that you must land immediately once you see an aircraft approaching.

An overview map for the recreational use of drones has been depicted in Figure 1. This image accurately presents where one is allowed to fly their drone for recreational use and where it is forbidden to fly a drone. An interesting observation that can be done from this image is that in many significantly sized cities, it is forbidden to fly a drone at all. Furthermore, for uncontrolled airports, flights within a distance of 3 kilometres are permitted, provided that there is no objection from the airport operator. Additionally, there may always be temporary bans and restricted areas for a limited time due to, for example, events.

Figure 1: Overview map for recreational flying with drones. Note that this map will change in March 2019.

There also exists a maximum weight for private drones of 25 kilograms. Making films and photographs with a drone may only be done for personal use. Here, the privacy right of others must be kept in mind. It is, for example, not allowed to film someone secretly. If pictures are being taken of a specific person or that person is being recorded, the person concerned must be informed. This leads us to the following point. The owner of a drone is responsible for any damage caused by their drone. This means that the owner of a drone is liable for any damages or injuries caused by their drone. Therefore, it is vital for the owner of a drone to verify whether their liability insurance covers any damage to drone incidents. In some cases, it is possible for the damage to run up to a substantial sum up to thousands of euros. We can further extend this by considering fines that can be given to drone pilots. Failing to abide by the rules mentioned above can result in either a warning or a fine. It is also possible for the controlled drone to be confiscated. The amount of the fine or the punishment is given depends a lot on the type of violation caused by drone usage. It will be considered if the drone was used in a professional setting or for hobby purposes. Furthermore, it will be considered if people were endangered or not.

The Dutch Government provides a summary in a visual form of what guidelines to follow during recreational usage of drones[49]. This visual can be observed in Figure 2. This figure accurately presents the most important rules to follow when using drones in a recreational setting. Note that the text on this figure is in Dutch.

Figure 2: A summary considering recreational usage of drones in Dutch.

### Commercial use

On the other hand, we can also consider the commercial use of drones. Examples include but are not limited to people that use the drone to earn money or people that use drones for business purposes. For these commercial users, different rules and regulations apply than for recreational users. A commercial user needs, for example, a license. The additional rules and regulations for commercial users must minimise the risk of accidents, both in the air and on the ground.

Examples of commercial uses include:

• Video production companies that make aerial shots.
• Making promotional films for a company.
• Using a drone for a business, such as companies that want to view hard-to-reach places for specific reasons.

For using a drone in a commercial setting, the owner of this drone needs an RPAS Operator Certificate (ROC). One can be requested from the Inspectie Leefomgeving en Transport' (ILT). If someone is piloting the drone, then this person also needs a pilot's license (vliegbrevet in Dutch). Furthermore, a certificate of airworthiness and proof of enrollment in the aviation register is needed[50]. There exist two sorts of ROC licenses, namely a regular ROC and a ROC Light. If a drone is heavier than 4 kilograms, then a ROC is needed. Otherwise, a ROC-light will be fine in most cases. Additionally, it is not allowed to fly as high with a ROC Light compared to a regular ROC.

Other differences are displayed in Table 2 below. Here, one can more clearly observe the differences between a ROC and ROC Light. We will not display all difference here as we save this for the next section where we also compare the commercial use to the recreational use.

Table 2: Differences ROC and ROC-light
Rules license Drone heavier than 4 kilograms Drone lighter than 4 kilograms
Maximal weight of drone allowed 150 kg 40 kg
Maximal flight height 120 metres 50 metres
Maximal distance between drone and owner 500 metres 100 metres
Minimal distance towards crowds 150 metres 50 metres
Minimal distance to buildings 150 metres 50 metres
Minimal distance to highways 150 metres 150 metres

If one does not abide by the rules, it is possible to obtain a fine and for the drone to be confiscated. People who do wrong more often can also get a prison sentence. The National Coordinator for Counterterrorism and Security (NCTV) focuses on the abuse of drones. The NCTV cooperates with national and international government organisations. Given fines can be around +/- 400 euros for commercial usage with a ROC Light and +/- 10 000 euros for commercial usage with a ROC.

### Summary

In this section, we provide a summary when considering recreational, commercial (ROC), and commercial (ROC Light) usage of drones. These rules and guidelines are from the most up-to-date version provided by the Dutch Government[51] (20-09-2016).

Table 3: Comparison of recreational and commercial (ROC and ROC Light) drone usage
Reacreational flying Commercial flying (ROC) Commercial flying (ROC Light)
Use of a drone Hobbyism, recreational use Commercial use Commercial use
Weight drone (total starting mass) Max. 25 kg Max. 150 kg Max. 4 kg
Priority for other air traffic Gives priority to all other air traffic and lands immediately when other traffic is approaching. Gives priority to all other air traffic and lands immediately when other traffic is approaching. Gives priority to all other air traffic and lands immediately when other traffic is approaching.
Visual Flight Rules Always in sight of the pilot Always in sight of the pilot Always in sight of the pilot
Distance to pilot or observer N/A Max. 500 metres Max. 100 metres
Daylight Only daylight Only daylight Only daylight
Height (from ground/water) Max. 120 metres. Some exceptions (KNVvL or FLRVC members): max. 300 metres Max. 120 meters (exemption possible in ROC) Max. 50 metres
Distance criteria: Exemption possible Exemption impossible
Distance to crowds Not above Min. 150 metres Min. 50 metres
Distance to buildings Not above Min. 150 metres Min. 50 metres
Distance to works of art, port, and industrial areas Not above Min. 50 metres Min. 50 metres
Distance to railway lines Not above Min. 50 metres Min. 50 metres
Distance to public roads and motorways Not above except for roads in 30 km zones within the built-up area and roads in 60 km areas outside the built-up area Min. 50 metres Min. 50 metres
Distance to vessels and vehicles N/A Min. 150 metres Min. 50 metres
Where are you allowed to fly? Not in controlled airspace Not in controlled airspace Not in controlled airspace
Not within 3 km of uncontrolled airports, unless there is no objection from the operator N/A Not within 3 km of uncontrolled airports, unless there is no objection from the operator
Not in the military and civilian low-flying areas, unless with an observer N/A Not in the military and civilian low-flying areas, unless with an observer
Proof of Authority for the pilot / driver ('brevet') N/A Certificate of Competence (RPA-L)(medical examination compulsory, at least LAP-L) Exemption Certificate of Competence Well: pilot can demonstrate sufficient competence, e.g., with a KEI diploma or a recognized pilot's license(this requirement does not apply if the drone weighs less than 1 kg) no medical examination
Certificate of Airworthiness for the drone N/A Certificate of Airworthiness (technical inspection required) Exemption Certificate of Airworthiness (no technical inspection)
Registration in aircraft register N/A Proof of registration Proof of registration
Minimum age N/A 18 years old 18 years old
Operational manual N/A Handbook necessary N/A
Insurance Not required WA insurance required WA insurance required
Notification obligation N/A 24 hours before the flight with Minister and mayor NOTAM N/A
Fines N/A +/- 10 000 euro +/- 400 euro

## Future regulation

Before reading the next text, keep in mind that most of the things elaborated on below hold as of now, but that they can change in the future when the final rules and regulations regarding drones are published. The introduction of mandatory knowledge requirements for recreational drone users will no longer take place at a national level. The primary regulation for EASA came into effect on the 11th of September, 2018[52]. This means that the responsibility for civilian drone regulations is transferred from the Netherlands to the European Union once the European regulations regarding drones come into effect. The Netherlands is, however, still responsible for the national implementation and execution of these regulations. It is expected that this regulation will be published in the June 2019[53] and will take effect early 2020[54]. Furthermore, there will most likely be a transition phase of roughly two years where national documents (licenses, et cetera) can still be used. The European drone regulations will replace the national regulations regarding airworthiness of drones, pilots of drones, and flight operations concerning drones. The moment these new regulations are active, the air traffic regulations for civilian drones laid down in the Regeling Modelvliegen' and Regeling op afstand bestuurde luchtvaartuigen' will be withdrawn.

The European rules are based on the risk that flying with a drone entails. There will be no more distinction between professional and recreational flying. The regulations will focus on different categories based on the risk involved for third parties both in the air and on the grond[52]. These categories consist of:

• the open category for low risk,
• the specific category for higher risk, and
• the certified category for the riskiest operations.

The operational conditions under which the flight is carried out, such as the flight altitude, determine the category in which a flight falls.

Note that there is a summary section below that summarises the different types of operations together with the different types of drones in a very concise and understandable way. One should go to these if one does not want to go into all the details regarding the types of operations and the types of drones.

### The EASA

While the preceding description provides a rundown of what to expect, it is possible to consider subcategories within the open category. It was decided by the European Aviation Safety Agency (EASA) to further partition operations in the open category into three subcategories to allow different types of operations without the need for authorisation[55]. This subdivision was made in Opinion No 01/2018 made by the EASA. The objective of this Opinion, as described in Opinion No 01/2018[55], is to create a new supervisory framework that defines means to alleviate the risk of operations in the:

• open category; through a mixture of limitations, operational rules, and requirements for the competency of the operator, as well as technical requirements for UAVs, such that the UAV operator may conduct the operation without prior authorisation by the competent authority, or without submitting a declaration, and
• specific category; through a system that includes a risk assessment being conducted by the UAVs operator before starting an operation, or an operator complying with a standard scenario, or an operator holding a certificate with privileges.

Additionally, the Opinion provided by the EASA intends to:

• implement an operation-centric, proportionate, risk- and performance-based regulatory structure for all UAV operations conducted in the open and specific categories,
• ensure a vast and uniform level of safety for UAV operations,
• foster the development of the UAV market, and
• contribute to addressing citizens’ concerns concerning security, privacy, data protection, and environmental protection.

The proposed Opinion will harmonise operations regulations in Europe and create a general EU market for drones. It will allow everyone to buy and operate a drone ensuring the following attributes:

• safety; by keeping drones away from crewed aircraft, protecting people and critical and sensitive infrastructure,
• security; by keeping drones at an appropriate distance from nuclear reactors; military bases or oil pipelines,
• privacy; using a proper separation from residential areas;
• environmental protection, by reducing the noise level.

### Consumer information

One of the novelties EASA has is the combination of product and aviation legislation in these new rules. In particular, design requirements for small drones (up to 25kg) will be implemented by using the well-known Conformité Européenne (CE) marking for products brought on the market in Europe. All European drones are assigned a CE-Marking. This marking consists of a number between 0 and 4, which specifies the class of the drone. We can then consider the following classes: C0, C1, C2, C3, and C4. Operators of drones will then find in each drone package a digital consumer information with the “do’s and don’ts” related to each class on how to fly a drone safely. These “do’s and don’ts” can be seen here. We provide an excellent overview of these classes together with the subcategories of the drones in the open category below.

### The open category

One of the conditions for the open category concerns a maximum altitude of 120 meters. For all drones more massive than 250 grams, requirements concerning the knowledge of the pilot are imposed on the pilot. Furthermore, product requirements apply to drones this category, such that it is reliable enough and has the right functionality, such as geofencing, on board. The open category probably includes recreational or professionally controlled drones with a mass of heaver than 250 grams and lighter than 4 kg. The operators of these drones will probably need a 'theory certificate'[54]. This certificate is comparable with the current Dutch theory certificate needed for mini-drones. It is expected that the (unqualified) Dutch mini-drone theory certificate can be converted into a European document or considered as valid without conversion. This also applies to those who fly a microdrone (max. 1 kg) and have an exemption for this (a ROC light permit). These operators still have more than two years to achieve that theory certificate. This certificate is only necessary if one wants to fly outside a model airfield.

In the Opinion mentioned above, which has been designed by the EASA, it was decided to subdivide operations in the open category into three subcategories further to allow different types of operations without the need for authorisation. The subcategories were defined according to the risks posed to persons and objects on the ground. Furthermore, these operations are all below 120m in height and far from aerodromes. The subcategories of the open category are:

• A1: flights over people but not over open-air assemblies of persons;
• A2: flights close to people, while keeping a safe distance from them;
• A3: flights far from people.

An overview of the requirements put on these subcategories together with the CE markings can be seen below in Figure 2.

Figure 2: An overview of the CE markings and the subcategories within the open category.

### The specific category

The specific category has no restrictions in advance such as a maximum height or not being allowed to fly over people. In the specific category, professionally controlled drones are considered that have a risk that is greater than that in the open category. This can, for example, be the flights for which a ROC is now required, which is the case when a drone is heavier than 4 kg[54]. If the operation carried out does not meet the requirements that apply to the open category, it will, in most cases, fall into the specific category. This holds unless there is a risky operation requiring a certificate (see below). For an operation in the specific category, the operator has to carry out risk analysis. Based on the results of this risk analysis, the operator must propose mitigating measures to keep the risk of the operation low enough. This analysis is then handed over to Inspectie Leefomgeving en transport' (ILT) which, after testing the analysis, can grant a license to the operator. Because there are no restrictions in the regulations in advance, this category offers considerably more opportunities for operators than the current national regulations. Flying above buildings, in the dark, out of sight of the pilot and even flying with an autonomous drone belongs in this category to the possibilities.

### The certified category

In the current proposals for European legislation (1 Nov. 2018), an operation falls into the certified category if the UAV is more significant than 3 meters and is flown over a crowd, when people are being transported by the UAV, and if hazardous substances are transported that can create dangerous situation in the event of a collision. We provide a concrete list below. Besides, if the risk analysis in the specific category shows that the risk of the operation is too high for the operation to be classified as the specific category, it is classified as the certified category.

Drones fall within the certified category if the risk of the intended flight is probably only to be controlled by setting strict requirements (through certification) on both the operator and the drone. This is the case, for example, with:

• flights with drone
• with which people are transported, or
• dangerous goods are transported where a high risk may arise for third parties in the event of a crash, or
• flights with large or complex drones:
• almost constantly above crowds,
• outside view distance, or
• in a part of the airspace where much other air traffic is present.

### What does this mean for us?

Drs. C. van Nieuwenhuizen Wijbenga, Minister van Infrastructuur en Waterstaat', stated that she is currently working on a plan for the national implementation of the European drones rules[53]. She further elaborates that she can finalise this plan and make it public once the rules are fixed at EU level. At that time, she will also organise a large information meeting to inform all national stakeholders in the drones dossier on the European rules and the national implementation plan. Her current estimate is that this meeting can take place in the first quarter of 2019. One of the components of this plan she proposes is the implementation at a national level of zones in which drones are not allowed to fly or are restricted. Before the establishment of these zones, the various stakeholders such as municipalities and the drones sector will discuss the criteria for zoning. The plan itself takes into account the transitional periods that will be included in the European regulations.

### Summary

In case one does not want to read all of the above text, we provide a concise summary here that considers all of the major elements that should be kept in mind when it comes to different types of operations and drones in the close future.

When it comes to drones use, we will (most likely) consider the following categories of operations:

Figure 3: An overview of the different categories of operations.

In-depth, these categories are as follows:

Figure 4: An in-depth overview of the different categories of operations.

When it comes to the open category, the various subcategories within the open category, and the various C markings, we consider the following:

Figure 5: An in-depth overview of the open category.

Figure 5 accurately depicts what a typical customer that is wanting to buy a commercial drone is interested in.

## Dangers

Let us consider a few of the dangers that various types of drones can impose on airports. We limit ourselves to two broad types of dangers that drones can introduce near airports. When we consider different types of airports on the Airports page, we take a deeper dive into the most considerable dangers that are introduced for each specific type of airport.

### Collisions with aeroplanes

It is possible for drones to collide with aeroplanes. Of course, smaller drones are more likely to inflict less damage upon the aeroplane than larger drones. In this section, we consider the possible types of damages drones, in general, can inflict upon aeroplanes as going in-depth about which drones can inflict what kind of damage falls outside of the scope of this project. Figure 3 provides a visualisation of the types of damage that can be inflicted upon aeroplanes by all sorts of drones.

Figure 6: Example of potential events following from a collision of a drone with an aeroplane. Retrieved from https://publicapps.caa.co.uk/docs/33/CAP1627_Jan2018.pdf.

If a collision between a drone and an aeroplane takes place, the damage inflicted upon the aeroplane can differ. There is a high probability that the drone in question will be destroyed. Then, it is possible for this drone to become unable to operate, which in turn, can result in that drone falling. Then, it is possible that someone or something gets hit by this drone, which could lead to the death of people and the destruction of things hit. Furthermore, a collision between an aeroplane and a drone can cause no damage at all, superficial damage, or severe damage to the aeroplane in question.

Below, one can observe a demonstration of a drone striking the nose cone of an airliner from the Crashworthiness for Aerospace Structure and Hybrids (CRASH) Lab at Virginia Tech. Note that the aeroplane is standing still in this scenario and that real collisions are bound to take place at higher speeds, which often results in more power being involved in the equation.

Figure 7: A demonstration of a drone striking the nose cone of an airliner from the Crashworthiness for Aerospace Structure and 3Hybrids (CRASH) Lab at Virginia Tech.

Let us ignore when no damage or superficial damage is inflicted as these types of damage do not put the aeroplane at significant risk. If, however, severe damage is inflicted upon the aeroplane, it is possible that component failures take place or that persons on board are injured. Component failure and injuries of people on board can lead to an unsafe landing. Additionally, if the pilots of the aeroplane get injured, it is possible for loss of control and an eventual crash of the aeroplane. Note that this is the worst case scenario, but that it is vital to consider these worst cases. In turn, an unsafe landing or loss of control can lead to more injuries of persons on board due to people walking over one another trying to escape the aeroplane or due to the crash.

All in all, we observe that drones can cause disastrous consequences when it comes to collisions with aeroplanes.

## Armed drones

Figure 5: An example of a weaponised drone.

It is possible that armed drones are used for planned attacks on airports. While this is a worst-case scenario to happen, it should still be considered, and measures should be taken against this scenario. These type of drones could be equipped with long-range weapons such that airport detection systems cannot detect them or with explosives. In the case that drones are equipped with explosives, it is possible for the drone to simply' infiltrate the airport and explode, which can put the lives of many people at risk. On the other hand, when long-range weapons are used, it is possible that the airport detection systems do not detect these drones. Then, these drones could freely attack the aeroplanes and also the airport. This, also, puts the lives of many people at risk. One example of a weaponised drone can be seen on the right-hand side.

# Solutions

In this section, we consider the requirements of solutions for the problem proposed in the specific problem description, all possible solutions, and both the advantages and disadvantages of each solution.

## Categories

When considering the state of the art research presented in the relevant Section, we can distinguish multiple categories in which the presented solutions might fall. In this Section, we further elaborate on these different categories, and as such provide a better overview and allow for more a more specific formulation of requirements. Firstly, different anti-UAV systems serve different purposes. For our study, we differentiate between the following purposes:

### Purposes

UAV Detection
These systems serve to detect the presence of UAVs in unwanted airspaces. They often also locate the UAV in question and sometimes include the possibility of continuous location tracking to assist systems categorised under the other purposes.
UAV Identification
Systems from this category serve to identify UAVs, obtaining more information about the UAV than simply its location. This information might include simple statistics, such as the average size of the drone which can often be observed by a human, given that the UAV is present in their field of view. More complicated statistics might also be obtained, such as a serial tracking number to identify commercial UAVs.
UAV Neutralisation
Drone neutralisation systems serve to neutralise a drone. This is the main topic of our study since UAV presence in the airspace above an airport introduces various risks, discussed in other Sections, that have to be neutralised in order to maintain public and societal security.

Now that the scope of the purpose of the anti UAV systems for airport security that we consider has become clear, we might further distinguish the main purpose considered in this study. As such, we differentiate between 3 different subcategories, all part of the drone neutralisation purpose. These categories are as follows:

### Categories

Preventative solutions
This category encompasses all solutions that serve to prevent the problem from occurring. More specifically, entries of this category focus on keeping UAVs away from airspace belonging to airports. An example might include the geofencing system that was described previously and will be elaborated on further in the following sections.
Corrective solutions
Solutions from this category focus on solving the problem of UAV presence in the airspace over airports, especially when said UAV is already present in that airspace. These solutions attempt to do so with minimal damage to the parties involved, an example might consist of a procedure where the control of the drone is overridden, either automatically or by a human, before the drone is removed from the airspace by landing or flight and after which control could be passed back to the pilot.
Destructive solutions
These solutions have the same area of focus as the previous category of corrective solutions, namely the minimising of further risk to air traffic above airports after a UAV has entered the airspace. The main difference is that, while corrective solutions attempt to do so in a non-destructive way, this limitation does not apply to destructive solutions. Sub-systems of a UAV or the UAV as a whole may be destroyed or permanently disabled. A coarse example consists of taking down unwanted UAVs with firearms, causing damage to the UAV and rendering it unable to continue operations.

This division into categories is not entirely black on white, however. Consider an abstract example system that temporarily incapacitates a UAV in flight, causing it to cease operation and enter a free fall towards the ground. This might result in the destruction of the drone, given the collision with the ground. We have found a grey area in our division into subcategories, and as such, we further define destructive solutions as those solutions, where the incapacitation of the drone follows from the destruction, and not the other way around. We also require the destruction to be an integral part of the solution, if we want it to count as a destructive solution. In this example, the destruction is not guaranteed nor does the incapacitation follow from the destruction. Instead, the destruction might follow from the incapacitation, dependent on other circumstances. Therefore, this specific example counts as a preventative or corrective solution, based on where the UAV in question is located. Note, however, that this is based on the keywords temporarily incapacitate'. If the incapacitation of the UAV or one of its subsystems were permanent, the destruction would be guaranteed since it does not depend on how hard the UAV hits the ground anymore. In this case, it would count as a destructive solution.

## Requirements

A solution to the specific problem described will have to adhere to requirements. These requirements are not simply capabilities the solution has to provide in the form of functional requirements, but they should also cover constraints posed on the solution. The constraints can be on the design of the solution in order to meet specified levels of quality, on the environment and technology of the system, and the project plan and development methods. Note that there can exist multiple different types of solutions and that we, therefore, have to keep the requirements of a solution as abstract as possible. We should not limit the solution space with these requirements. Instead, we should provide a general outline of what capabilities (functional requirements) the solution should provide and under what constraints (non-functional requirements).

Furthermore, these requirements might serve as a basic framework for further development of solutions to similar problems, thereby widening the scope to other problem spaces involving UAVs as well.

In this case, it is rather simple to provide some basic requirements and let the input of the airports' decide on further requirements.

For detection, the solution should be able to detect UAVs. For identification, the solution should be able to identify a detected UAV. For Neutralisation, the solution should be able to neutralise the detected and identified UAV. Of course, there are many other requirements, but we let the airport place these requirements as certain airports might argue that the safety of bystanders is more critical than other airports, such as recreational airfields.

## Possible solutions

As we have already elaborated on, a possible solution can be categorised into the purpose it fulfils with respect to anti-UAV systems at and around airports. Since a full anti-UAV system should be able to do three things: detect flying objects, identify that this object is an (unwanted) UAV, and lastly neutralisation of the UAV. However, the identification of the object might be something that is up for discussion, since it might be safer to neutralise every flying object, we will discuss this later on. As most possible (partial) solutions only cover one or two of the three things it should be able to do, before it can be considered at a full anti-UAV system, for each of the (partial) solutions listed below, they are divided up into categories of its purposes it fulfils. Such that, later on, we can compare and afterwards combine multiple of these partial solutions into one system that meets the needs of the users.

#### UAV Detection

• Radar system for detecting the location and height of an object in the air. The radar makes use of a transmitter which produces an electromagnetic signal which is radiated into airspace with an antenna. If this signal hits an areal object, it will get reflected in many directions. This reflected signal is received by the radar antenna then it is processed to determine the geographical data of the object.[2]
• A Wi-Fi receiver can be used to detect a UAV based on the signature of the signal reflected from the propellers of a UAV. Similar to radar, a transmitter broadcasts signals and a receiver captures reflected signals that bounce of a UAV. [3]
• Detect a UAV by listening to the communication channel between the UAV and its controller using a wireless receiver. Usually, UAVs 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 UAV's presence. [3]
• Detection of UAVs with the use of other UAVs that fly around the airports, carrying lightweight radar systems or cameras to scan their environment.
• Echodyne's 3D Security radar that offers superior sensor performance in a compact, solid-state, all-weather product. A recent winner in the SOFWERX Game of Drones competition.
• Human detection, for example by using watchtowers or pilots in the aeroplanes to spot UAVs. (Currently what Eindhoven Airport uses to detect UAVs)
• 3D Radio frequency antenna (https://drone-detection-system.com/the-system/)

#### UAV Identification

• Identification of any specific aircraft can be made by 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 are able to broadcast coded signals for identification, for this solution to work. [2]
• For identification of UAVs, 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 UAVs and other moving objects. Where it rejects non-UAV 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. [11]
• 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. [12]

#### UAV Neutralization

• Taking out UAVs by using air to air missiles, where these air missiles could be launched from other UAVs used by the airport or possibly any other aerial vehicle.[2]
• Taking out UAVs or disabling specific subsystems might be achievable by using lasers. Different kinds of lasers can be used for different purposes, either permanently or temporarily disabling a UAV. [2]
• Electromagnetic attacks to interfere with the GPS signals of the UAV, that the UAV uses to position itself. Jamming the GPS signals causes the UAV not to be able to follow the pilot's navigation commands accurately.[2]
• Taking control of a UAV by spoofing the GPS signals of the UAV, such that the UAV thinks that it is still talking to the original pilot when it is actually being taken over. This way the drone can easily and safely be landed somewhere out of danger.[2]
• Capturing a UAV using another UAV carrying a net, which drops the net over the unwanted UAV. Thereby taking control of the UAV as the net makes sure the UAVs rotors get tangled in the net making sure it is unusable for the pilot. Then with a parachute on the net, it can be made sure that the UAV lands safely on the ground[7]
• A bazooka with an intelligent locking system to aid the controller to hit the UAV successfully, that shoots a net to capture a UAV. The rotors of the UAV will then get tangled in the net, making sure it cannot cause any harm anymore. Then a parachute that is attached to the net will make sure that the UAV will land safely on the ground. [8]
• Transmitting geo-fence coordinates, avoidance commands or disruption of radio communication in order to avoid UAV's entering no-fly zone. [17]
• Using trained eagles to neutralise UAVs. These eagles would be trained into considering UAVs as preys so that they could catch these drones and place them in a safe area. [38]
• Geo-fencing software built into the UAVs restricts consumer UAVs even to be able to fly within a certain range of unwanted areas such as airports. [56]
• Using high powered radio waves to disable drones, it blocks their communication with the controller and switches them off mid-air. [39]

### UAV Detection

Echodyne designs and manufactures radars with unparalleled price-performance. MESA technology is used, which is a fundamental breakthrough in high-performance radar with game-changing benefits in many markets. Acuity is an intelligent radar control software suite to enable user configurability. At an order of magnitude lower cost, Echodyne radar radically outperforms all other radar sensors in its class[57]. Their 3D Security radar offers superior sensor performance in a compact, solid-state, all-weather product. A recent winner in the SOFWERX Game of Drones competition, EchoGuard is the perfect' radar for a multilayered perimeter defence solution. Furthermore, Acuity API integrates seamlessly with existing security ecosystems to provide situational awareness.

Their radar can be seen in usage in the following video. Echodyne provides another video that depicts a visualisation of the working of their radar.

The specifications of the 3D Security radar are as follows:

• Size: 8.0in x 6.4in x 1.57in (20.3cm x 16.3cm x 4cm)
• Weight: 1.25kg
• Power: DC +15V to +28V
• Operating: <50W
• Hot standby: <15W
• Hibernate TBR: <100mW
• Field of View: 120° Azimuth x 80° Elevation

This radar reliably detects and tracks aircraft and cars at 3km, people walking at 2km, and sUAS at 1km.

The Guardian reported that one such system could cast around 150 000 dollars[58].

WiFi receivers can accurately determine the position of drones. They are, however, very susceptible to interference. For example, WiFi signals can be blocked by obstacles. While it might be sufficient for right now, it is possible for malicious attackers to attach WiFi interfering tools to their UAVs. Then, WiFi receivers might not be as reliable in the future. When it comes to solutions, reliability is one of the main concerns as the solutions has to work in all cases.

Listening on communication between drone and ground

Listening to communication between a drone and its operator can be an easy way to detect the presence of both the drone and the operator. Often, this type of communication is not encrypted. The U.S. government displayed how easy it is to hack drones made by Parrot, DBPower, and Cheerson[59]. One significant disadvantage, however, is that custom built drones might use significantly different communication standards which do make use of encryption. So this solution is only useful when the communication is not encrypted, which still happens quite often as of now. The number of communications that do make use of encryption is suspected of increasing with the years as the technology gets more established. Then, this solution does not provide a way of detecting drones.

Detecting drones with other drones

When we use drones to detect other drones, we do not depend on insecure channels. With this solution, we are not just limited to drones in the line of sight as the drone-detecting drone can fly around. A disadvantage, however, is that flying around with a drone at a busy airport can be quite dangerous. Furthermore, these drones can only stay in the air for a limited time due to battery-related constraints. This can be mitigated by simply using larger batteries, but this increases the weight of the drone, which leads to some negatives again. This might, however, still provide to be a sound solution as it makes dealing with the illegal drone activity easier as the drone itself can, for example, be weaponised.

### UAV Identification

Identification by coded signal

UAV identification through coded signals can quickly identify activity. A disadvantage, however, is that other areal entities, such as bird, might also be targeted. This is due to birds being able to be roughly similarly sized as drones. Thus, this method can identify the aerial activity, but there is no guarantee that only illegal drone activity is identified. Then, this could lead to negative results when we consider, for example, birds. It is possible they are targeted by the drone interception system.

3D radar system with machine learning

UAV identification through a 3D radar system that uses machine learning can eventually lead to a precise system. The issue with it is that it first needs data to learn from. The gathering of this data can provide to be difficult. Furthermore, even if it learns from this data, it does not always have to lead to correct results as there are, often, biases in data.

UAV identification through an X-band radar system can perform accurate shape analysis of flying objects using doppler and high-frequency radar signals. Attaching a radar system to a drone, however, can be an issue around airports as this might result in interference with already existing systems.

### UAV Neutralisation

Missiles

The use of missiles might, on the one hand, be a rapid method and affordable method to take out hostile drones. However, there are a few downsides to this method. First of all, missiles are very dangerous, especially in an area where, apart from hostile UAVs, many aeroplanes with innocent passengers fly. The chance exists that a missile might miss an unwanted UAV and, instead, hit an aeroplane. Which would be disastrous and would only make the situation worse, especially if the unwanted drone was just a hindrance to the airport. UAVs are often quite small and can move/switch directions pretty quickly it is actually quite hard for a missile to correctly take out a UAV. Furthermore, might the unwanted UAV actually be taken out by a missile, then it will most definitely be destroyed meaning that police investigation will be more difficult. All in all, the use of missiles at and around airports is most likely a bad idea.

Lasers

Lasers are very precise and can be used in multiple ways to deal with drones. On the one hand, a very narrow laser beam can be pointed at an unwanted UAV to melt the body of the UAV causing structural failure and crashing of the UAV. On the other hand, a wide laser beam can be used to target multiple unwanted UAVs at the same time, taking out their control systems causing them to crash. Both methods require pretty close range to a target, the exact range depends on the type of laser that is used, and clear sight to the targetted UAV(s). However such systems could be attached to moving vehicles making such systems very mobile. Another advantage is, compared to the use of missiles, is that there is no need to reload as it uses the energy of a generator or the vehicle it is attached to. However, this means that the energy could deplete might there be too many targets, or might a target take too long to take out. Also, one might not always have clear sight to a target, or the range might be too long, making this method ineffective.

Interfering with GPS

Interfering with the GPS of a UAV, will not cause any harm to the drone. Then the drone can be inspected, once landed, to find out who is responsible for the UAV. However, when interfering with the GPS of a UAV, the pilot will be unable to send commands to the UAV making the UAV uncontrollable. This might cause the UAV to crash into aeroplanes, buildings or crowds of people. Hence this method can only be used when a UAV is in a so-called 'safe space' where it cannot harm anyone/anything. Furthermore, GPS interference might also affect the GPS systems of the aeroplanes at the airport. It might be the case that this method of neutralisation will not work against every UAV, as some UAVs might not use GPS to communicate with its pilot. Also, if a UAV is autonomous, it does not even need communication with a pilot necessarily. Lastly, it might also be difficult to get regulatory approval for the use of jamming devices due to jurisdictions.

GPS spoofing

This method is similar to the method discussed above (Interfering with GPS) and thus also shares the most advantages and disadvantages. However, an advantage of this method compared to GPS interference is that the targetted UAV will not be uncontrollable, but instead, the UAV can just be safely landed on the desired location. Apart from that, it shares the same disadvantages as GPS interference.

Capturing UAVs using nets underneath other UAVs

This method is a method that is not harmful to UAVs/the surroundings and does use interference which might cause problems for aeroplanes at the airport; those are two significant advantages. Another advantage is that it is a very affordable method to deploy to counter unwanted UAVs and allows for safe retrieval of UAVs. However, UAVs carrying a net to capture hostile UAVs, mostly just have room for carrying a single net to capture a hostile UAV. Meaning that if the UAV misses the net, it needs to return and completely be reset. Another thing is that these UAVs need to be able to follow small and very fast hostile UAVs to be able to place a net over them. This might be quite an issue, since carrying a net might be pretty heavy for a UAV causing it to move more slowly. Lastly, using this method, there will be even more UAVs in the air space, meaning even more interference for the airport.

Bazooka net system

This method is quite similar to previously mentioned method (Capturing UAVs using nets underneath other UAVs), however, in this case instead of using a UAV carrying a net, it uses a bazooka to capture a hostile UAV. It will also be quite affordable and straightforward to implement. Another advantage of this method is that there will not be any extra UAVs in the air space which might cause more interference. However, this method might be more inaccurate since a net needs to travel in the air for a more extended period before reaching an unwanted UAV, giving the UAV more time to evade the net. Furthermore, a bazooka firing a net will have more limitations in its range compared to UAVs carrying a net as it might not be able to reach unwanted UAVs which are high up in the air space.

Geo-fence coordinates

This method is the most straightforward solutions for the airports, as they will not need to implement a system to neutralise UAVs since UAVs simply will not be able to enter the air space of airports. However, this method is dependent on drones being programmed not to enter certain areas and will therefore not always avoid unwanted UAVs at airports. This might help against unwanted consumer UAVs that accidentally enter the air space above airports due to ignorant pilots. However, if someone really has terrible intentions with an airport, it will be straightforward to either turn off the geo-fencing software on a UAV or simply design their drone which will not have any geo-fencing software either. Furthermore, the software of the UAVs must continuously be updated according to new areas that might not be entered by UAVs, which might not be possible. Lastly, this solution also does not help against a large number of UAVs that already exist and can still be used for interference at airports. So in summary, this method might be useful for taking on a large part of newly bought UAVs, but can easily be avoided and should not be relied on by airports as the only method against UAVs.

Eagles

Using eagles to intercept drones is an economically friendly solution. Furthermore, the chances of a technical malfunction are non-existing. It is, however, still possible for the birds to deviate from the standard procedure when intercepting a drone even after extensive training. Moreover, flying birds near and around airports can be dangerous as they can get damaged by aeroplanes and other obstacles.

The Dutch police started using eagles to intercept drones back in 2016 already[60]. This, initially, seemed like a successful approach to seize drones mid-air. Not long after their initial usage, the Dutch political part Partij voor de dieren' expressed their concerns regarding the safety and the wellbeing of the eagles.

After a year of training the birds, the police have concluded that the Eagles were barely used. Furthermore, the NOS reports, the training of the eagles is more complex and more expensive than the police expected. Additionally, there was little to no return in training these birds. Moreover, the birds did not always follow the procedures they were instructed to follow and therefore, the police was not convinced the birds would follow these procedures in real use[60].