Most LiDAR systems use four main components:
Lasers are categorized by their wavelength. 600-1000nm lasers are more commonly used for non-scientific purposes but, as they can be focused and easily absorbed by the eye, the maximum power has to be limited to make them ‘eye-safe’. Lasers with a wavelength of 1550nm are a common alternative as they are not focused by the eye and are ‘eye-safe’ at much higher power levels. These wavelengths are used for longer range and lower accuracy purposes. Another advantage of 1550nm wavelengths is that they do not show under night-vision goggles and are therefore well suited to military applications.
Airborne LiDAR systems use 1064nm diode pumped YAG lasers whilst Bathymetric systems use 532nm double diode pumped YAG lasers which penetrate water with much less attenuation than the airborne 1064nm version. Better resolution can be achieved with shorter pulses provided the receiver detector and electronics have sufficient bandwidth to cope with the increased data flow.
Scanners and Optics
The speed at which images can be developed is affected by the speed at which it can be scanned into the system. A variety of scanning methods are available for different purposes such as azimuth and elevation, dual oscillating plane mirrors, dual axis scanner and polygonal mirrors. The type of optic determines the resolution and range that can be detected by a system.
Photodetector and receiver electronics
A photodetector is the device that reads and records the signal being returned to the system. There are two main types of photodetector technologies, solid state detectors, such as silicon avalanche photodiodes, and photomultipliers.
Navigation and positioning systems
When a LiDAR sensor is mounted on a mobile platform such as satellites, airplanes or automobiles, it is necessary to determine the absolute position and the orientation of the sensor to retain useable data. Global Positioning Systems provide accurate geographical information regarding the position of the sensor and an Inertia Measurement Unit (IMU) records the precise orientation of the sensor at that location. These two devices provide the method for translating sensor data into static points for use in a variety of systems.