# Advanced Progress of Optical Wireless Technologies for Power Industry: An Overview
## 2 Classification and Progress of Power Industry Optical Wireless Communications
### Optical Wireless Power Inspection  
#### 2.5.1 Two Ways of Power Inspection  
Compared with the traditional power inspection methods, unmanned aerial vehicle (UAV) power detection line is more efficient and safer to operate in the forests, deep mountains and forests, rivers and lakes. In terms of operation precision, the UAV power line also gradually achieves the effect of accuracy that is comparable to the professional camera. UAV aerial survey could clearly study and judge the line loss parts that are hard to find by human eye. There are two main methods for power inspection: one is the visible/photoelectric pod detection carried by a multi-rotor UAV, mainly solves these problems such as insulator damage, needle, wire damage, temperature anomaly detection problems. The other is the secondary power channel data with multi-rotor/v TOL equipped LiDAR, which mainly solves the problems of tree barrier detection, cross crossing detection, tree growth analysis, power detection, and so on. Combined with the two inspection methods, how to solve the need of regular inspection and fine inspection at the same time to improve the efficiency of operation.  
Compared with fixed-wing UAVs, multi-rotor UAVs fly at a low speed and have the function of hover on the fixed point. They could observe specific inspection targets in detail, which is conducive to defect discovery, such as insulator burst, wire broken strand, wire icing, bolt detection, foreign body suspension, etc. Since the defect inspection of the tower needs to observe the insulators, bolts, wires, and other special details, the traditional manual inspection has to climb up the tower to inspect with electricity, which is extremely dangerous. The multi-rotor UAV may hover around the tower and take pictures of the tower from all directions, which is undoubtedly a revolution of power inspection.  
Figure 24: Experimental setup used for coupling efficiency measurement [79].  
The multi-rotor UAV inspection system consists of two parts: UAV flight platform and ground station. The flight platform includes the fuselage, power supply, propeller, flight control system, cradle head, camera, and image transmission system. The ground station includes surveillance and observation systems that monitor the UAV's flight status (such as batteries, number of satellites, flight path, altitude, etc.,) and receive high-definition video signals sent by the UAV. The operator could use this information to control the UAV to capture target images and video information in real-time; the evening after sunset and when on a cloudy day it does not rain. Generally, it is better to fly along the wire above the wire side when the plane is patrolling, and the plane and the sun should be on the same side of the wire to avoid backlight. The axis of the lens should be at an angle with the horizontal plane and less than 100 m away from the wire. The orientation of the lens (usually autofocus) is usually fixed on the ground in advance and does not change during flight. If change is needed, it is achieved by changing the flight path of the aircraft. If there is a very complex gyro stabilization system platform on a moving vehicle, it can realize automatic positioning and use images to accurately analyze the transmission route.  
Finally, the use of autonomous satellite navigation control, geographic matching line automatic control, automatic tracking of the line tower, and flight control functions, so that the drone can patrol to follow the flight control according to the transmission line, altitude, and direction angle of the fully automatic line, making the drone close to the body patrol work on transmission lines.