Overview: LiDAR is a kind of active detection technology, which can acquire the three-dimensional spatial information of the target accurately and quickly. As an active imaging system, three-dimensional imaging LiDAR has the advantages of obtaining high-precision distance dimension information and not being restricted by light conditions compared with passive imaging systems, and compared with the microwave radar imaging system, it has the advantages of high angular resolution, high measurement accuracy, strong anti-interference ability and easy miniaturization. Due to its unique technical advantages in object recognition, classification, high-precision 3D imaging and measurement, it is widely used in military, aerospace and civil 3D sensing and other fields. With the development of laser and detector, various range measurement techniques and 3D imaging LiDAR systems are flourishing, and the application scope and development prospect of LiDAR are quite broad. Recently, 3D imaging LiDAR systems are gradually developed from single point scanning to small array scanning, line array sweep and planar array flash imaging. At the same time, the single photon detection technology is becoming mature and the detection sensitivity of 3D imaging LiDAR is getting higher and higher. With the development of modern detection technology more and more inclined to the fusion detection of various sensors, the development of 3D imaging is also inclined to the combination of active and passive imaging to obtain more abundant target information.

According to the imaging mechanism, the 3D imaging LiDAR systems can be divided into scanning imaging LiDAR system and planar array LiDAR imaging system. According to the laser distance measurement mechanism, it can be divided into direct pulse ranging, phase ranging and linear frequency modulation ranging. Different mechanisms of LiDAR 3D imaging system have different advantages and disadvantages. In this article, the principles of various LiDAR detection and 3D imaging systems are introduced, and the foreign and domestic development status of single point scanning, linear array sweeping and planar array 3D imaging LiDAR systems are summarized and sorted out. Meanwhile, their technical characteristics, advantages and disadvantages in different platforms and application fields such as spaceborne, airborne and vehicular platforms are compared and analyzed. In addition, it should also be recognized that 3D imaging LiDAR as a means of detection also has its shortcomings. For example, compared with passive camera imaging systems, its horizontal resolution is not high and it lacks target texture information, compared with the microwave radar, it is more susceptible to atmospheric conditions such as cloud, fog and haze. In the design and application of LiDAR systems, one should give full consideration to the actual need, try to avoid its weakness and take its advantages. It will be a good choice for combining LiDAR with visible/infrared passive imaging cameras and only taking the point of interest/controlling for fast and accurate ranging, which can make full use of their respective advantages. Hoping this article can provide some reference for readers to understand the development and design of modern 3D imaging LiDAR systems.