Fig. 1. Single photon detector. (a) 189 pixel×600 pixel SPAD array by Sony, Japan^[8]; (b) 4 pixel×4 pixel SiPM detector by Israel Institute of Technology^[10]

Fig. 2. Progress in lightweight type-aware LiDAR scanning technology. (a) MEMS LiDAR by Toyota Central R&D Labs, Japan^[12]; (b) MEMS scanner array with 23 mm aperture by Fraunhofer Institute for Photonic Microsystems, Germany^[15]; (c) OPA chip by Analog Photonics, USA^[16]

Fig. 3. Fiber coupled 5 pixel×5 pixel flash LiDAR by Guilin University of Technology^[20]

Fig. 4. Performance comparison of array LiDARs based on SoC

Fig. 5. Superiority of the EMD and VMD algorithms for processing nonlinear and non-stationary signal. (a) Denoising effects of EMD based on different criteria^[62]; (b) denoising effects of EMD and VMD^[67]

Fig. 6. Distortion and correction results of MEMS two-dimensional galvanometer scanning^[87]. (a) Actual scanning image；(b) distorted image of grid test target; (c) grid image after distortion correction

Fig. 7. Angle errors of the front and back points comparing the effectiveness of the two-face, the length-consistency and the network methods^[96]. (a) Horizontal angles; (b) vertical angles

Fig. 8. Calibration based on cylindrical target^[102]. (a) The whole Velodyne point cloud; (b) layer and density segmentation; (c) 2D Hough circle detection (green); (d) radius histogram examination; (e) cylinder extraction (green dash) followed by cylinder fitting with blunder detection (magenta); (f) the segmented cylinders (blue)

Fig. 9. Schematic diagram of classification for lightweight type-aware LiDAR

Fig. 10. LiDAR systems in space exploration. (a) XSS-11 spaceborne scanning LiDAR system^[110], Canada; (b) LiDAR system of Chang’e 3^[118], China; (c) LiDAR system of Hayabusa2^[119], Japan; (d) ALHAT flash LiDAR^[120], USA; (e) OSIRIS scanning LiDAR^[122], USA