# Collaborative Unmanned Vehicles for Inspection, Maintenance, and Repairs of Offshore Wind Turbines
## 2 The State-of-the-Art of UVs Performing in OWT IMR Operations
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Types** & **Ref.** & **Purposes** & **Methods** & **Application** \\ \hline
[44] & Recovery & - & Using a fiducial marker located on a USV for accurate UAV landing. & General \\ \hline
[45] & Recovery & - & Using a three-stage fiducial marker on a USV to improve landing stage detection by UAVs. & General \\ \hline
[46] & Communication platform & - & Using a distributed dynamic network topology for fulfilling effective communication for establishing required formation between UAVs and USVs based on an ad hoc network. & General \\ \hline
[47] & Path planning, navigation, communication platform & - & Using aerial mapping and real-time aerial visual assistance provided by UAV for USV path planning and safe cruising. & Monitoring of rivers and dams \\ \hline
[48] & Recovery, transportation & - & Using adjustable buoys and a unique carrierdeck for safe landing and transporting of a UAV on a USV. & General \\  & & - & Using 3D path planning by generating a sequence of guide points for a UAV towards the USV deck. & General \\
**UAV-USV** & & - & Using integrated ultrasonic sensors on a USV to ensure UAV landing positioning accuracy. & General \\ \hline
[49] & Recovery & - & Using an infrared receiver on a UAV to detect infrared beacons & General \\  & & - & Using a two-phase UAV precise landing method to land on a USV. & General \\  & & - & Using USV control and path-following algorithms to guide UAV. & General \\ \hline
[50] & Launch and recovery & - & Using a robotic recovery system for a water-landing UAV & General \\  & & - & onto a USV. & General \\  & & - & Using a solar-powered automated USV platform. & General \\ \hline
[51] & Communication platform & - & Using location-based beam steering algorithm to establish high-speed communication links between a GCS, a USV, and a UAV. & General \\ \hline
[52] & Power supply & - & Using a wireless charging pad on a USV platform to charge & Monitoring of water pollution \\  & & - & UAV’s batteries. & General \\ \hline
[53] & Power supply & - & Using power umbilical tethers from a USV to supply power which results in longer UAV flight time. & General \\ \hline
[54] & Localization & - & Using an Extended Kalman Filter (EKF) augmented by ultra-short baseline (USBL) range and visual-data-based localization from a USV to enhance UUV localization. & General \\ \hline
[55] & Launch and recovery & - & Using a stern platform to recover a UUV onto a USV. & Surveying of ports and critical \\
**UUV** & & - & Using optical communication from a UUV to the USV to send back sonar data and underwater positions. & General \\ \hline
[56] & Recovery & - & Using visual lighting and acoustic guidance strategies for the & General \\  & & - & Docking and Line Capture Line Recovery (LCLR) system to recover & \\  & & - & a UUV onto a USV. & General \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of UAVs collaboration types, purposes, and methods. From Table 1, it can be summarized that collaborative UVs can be used to solve many challenging issues surrounding unmanned operations such as communication, launch and recovery, localization and navigation, power supply, and transportation. Most of the works focus on solving unmanned operations that can be applied to many areas without focusing on a specific application. However, several works have demonstrated using UVs in a collaborative manner to solve unmanned operations in areas such as surveying, search and track, monitoring, and inspection. Up to the current date, no research work has demonstrated successful implementation of collaborative UVs within the OWT sector, rather focusing on future views and directions [24]. By deploying collaborative UVs, it can immensely simplify and solve many issues faced by a single UV or by manual operators in performing OWT maintenance and repairs. The major enablers or opportunities that might arise have the ability to perform complex IMR tasks as well as gaining a more accurate and reliable localization and navigation system.