## 3 UAV Solutions in Greenhouses
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**No** & **Study** & **Study Name** & **Task** & **Year** & \
\begin{tabular}{c} **Product/** \\ **Focus** \\ \end{tabular} &
\begin{tabular}{c} **UAV** \\ **Type** \\ \end{tabular} \\ \hline
1 & \
\begin{tabular}{c} [PERSON], [PERSON], [PERSON], [PERSON], \\ [PERSON] and [PERSON] [93] \\ \end{tabular} &
\begin{tabular}{c} Study on Assistant Pollination \\ of Facility Tomato by UAV \\ \end{tabular} & Pollination & 2019 & Tomato & Single UAV \\ \hline
2 & \begin{tabular}{c} [PERSON], \\ [PERSON], \\ [PERSON], [PERSON], [PERSON] and [PERSON] \\ \end{tabular} & \
\begin{tabular}{c} Heterogeneous Multi-Robot \\ System for Mapping \\ Environmental Variables of \\ Greenhouses \\ \end{tabular} & Mapping & 2016 &
\begin{tabular}{c} Environmental \\ variables \\ \end{tabular} & Single UAV \\ \hline
3 & \begin{tabular}{c} [PERSON], [PERSON], [PERSON], \\ [PERSON] and \\ [PERSON] [86] \\ \end{tabular} & \
\begin{tabular}{c} Mini-UAV Based Sensory \\ System for Measuring \\ Environmental \\ Variables in Greenhouses \\ \end{tabular} & Monitoring & 2015 &
\begin{tabular}{c} Environmental \\ variables \\ \end{tabular} & Single UAV \\ \hline
4 & \
\begin{tabular}{c} [PERSON], [PERSON], \\ [PERSON] and \\ [PERSON] [92] \\ \end{tabular} &
\begin{tabular}{c} Navigation and Applicability \\ of Hexa Rotor Drones in \\ Greenhouse Environment \\ \end{tabular} & Navigation & 2018 & Positioning & Single UAV \\ \hline \hline \end{tabular}
\end{table} 
Table 2: UAV studies in the greenhouse for precision agriculture. application, UAVs can collect environmental data in the greenhouse and perform mapping. In this way, UAVs, which can make yield estimates and monitor plant health, can provide great advantages for greenhouse workers thanks to their low cost and availability. Founded by four friends who are aware of these advantages, Applied Drone Innovations (ADI) ([[http://applieddroneinnovations.nl/](http://applieddroneinnovations.nl/)]([http://applieddroneinnovations.nl/](http://applieddroneinnovations.nl/)) (Accessed date: 6 December 2021)) in the Netherlands has developed UAV prototypes that monitor plant growth and environmental factors such as temperature, humidity, carbon dioxide, brightness and volatile organic compounds in the greenhouse [95] (see Figure 6b). They increased the effectiveness of UAVs in the greenhouse with tasks such as localization and flight path optimization in the indoor area of the greenhouse. In February 2020, Dutch drone developer PATS ([[https://pats-drones.com/](https://pats-drones.com/)]([https://pats-drones.com/](https://pats-drones.com/)) (Accessed date: 6 December 2021)) introduced a bat-like UAV solution system with video to eliminate insect pests in the greenhouse environment (see Figure 6c). The aim was to maintain the ecological balance in a greenhouse ecosystem by eliminating pests with autonomously operating UAVs. Although the usability and importance of the UAV in the greenhouse are obvious, greenhouses are a difficult flight environment for the UAV due to their natural structure. Greenhouse operators want to benefit from the labor savings, efficiency and business advantages that UAVs can offer, but they hesitate about the reliability of these systems. Indeed, it is difficult to carry out autonomous UAV studies in an indoor environment. Moreover, the type of plant grown is also a major factor in operating the UAV in the greenhouse. It is much more difficult for the UAV to perform tasks in situations in which plants grow taller, plants overlap with each other and obscure the view of other plants, or greenhouse rope is used for plants. However, apart from such situations, autonomous UAV missions for the greenhouse make quite a lot of sense. While the outdoor applications of UAVs are many since they are reliable and easy, the use of UAVs in closed areas such as greenhouses is still limited today. However, its wide application range, low cost, versatility and precision indicate a promising future for UAVs in indoor farming.