# Computer Vision for Fire Detection on UAVs--From Software to Hardware
## 1 Introduction  
Unmanned Aerial Vehicles (UAVs) in recent years have been the center of many studies. They are aerial robotic vehicles that are capable of high speeds and carrying heavy loads. Due to their maneuverability which makes them capable of avoiding easier obstacles and flying above them, unlike ground-based robots, they are ideal for many applications. Some of these applications are: infrastructure monitoring and inspection, earth science, defense and security, agricultural and in applications of environmental interest [1]. Research on UAVs has led to the development and design of different types of vehicles that differ in a variety of characteristics, such as weight, size, mode of operation and flight, engine type and mechanisms involved in the vehicle. Two main categorizations that have been made in UAVs concern their weight and flight mode based on their aerodynamic design. Based on their weight [2], UAVs can be distinguished according to the characteristics of Table 1 in Super Heavy, Heavy, Medium, Light and Micro. This categorization has an impact on further categorizations of UAVs, such as the variation in the volume or type of engine that powers their system. \begin{table}
\begin{tabular}{c c} \hline \hline
**Type** & **Weight** \\ \hline Super Heavy & W \(>\) 2000 kg \\ Heavy & 200 kg \(<\) W \(\leq\) 2000 kg \\ Medium & 50 kg \(<\) W \(\leq\) 200 kg \\ Light & 5 kg \(<\) W \(\leq\) 50 kg \\ Micro & W \(\leq\) 5 kg \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Classification based on weight. Another classification can be done regarding their mechanical design. Based on this, there are four main categories. These are Fixed wing, Flapping wing, Multicopter and Single rotor [3; 4; 5]. _Fixed wing_: Models in this category use wings that have one or more propellers to move in the environment and a runway is mandatory for takeoff and landing procedures. The change in their course depends on a combination of movable surfaces and thrust. These models compared to the other types of UAVs can travel with high speed carrying heavy payloads [6] and, due to the design of their wings, they cannot be easily adapted to wind conditions. _Flapping wing_: This category includes vehicles that have many common features with the UAVs of the previous category. The difference is inside the mechanism that exists in the wings which facilitates the change of direction of the vehicle and helps increase the lift. Their increased maneuverability makes them more flexible than fixed wing models, in cases where there are strong winds. Models in this category require also a runway for taking off and landing. _Multicopter_: This category of UAVs differs in many aspects from the previous two. The operation of the multicopter is based only on the rotors it has, as it has no wings at all. They are capable of vertical taking off and landing and do not require any kind of runway. Its rotors are mounted horizontally on the main body of the vehicle and the models have increased stability and are able to adapt to flight conditions and constantly change their speed. _Single rotor_: This category includes models with a single central rotor and a tail rotor. They share the same features as multicopters except that they are more unstable models. The various classifications in UAV show that every category has its own pros and cons. As a result, the suitable platform selection varies and depends on the application. The applications using UAV capabilities are many and differ in their structure and purpose. More specifically, different types of UAVs have been used in applications, such as agriculture, inspections, delivery supplies, rescue operations, surveying, filming, military applications and disaster or hazards identifications. One application that belongs to the group of implementations related to hazard monitoring and prevention is fire detection. With the help of UAVs, fires can be detected early or even before they start.