Fig. 1. Composition and principle of distance gating system. (a) The principle of backscattering^[21]; (b) detection system composition^[22]; (c) distance gate system equipment composition

Fig. 2. Range strobe equipment and imaging results. (a) Range gate device diagram; (b) depth map of the target image obtained using the range-gated device

Fig. 3. The principle diagram of photon counting lidar. (a) Gen-1 photon counting lidar schematic diagram^[34]; (b) SPAD detection process diagram^[35]; (c) underwater photon counting lidar system^[9]

Fig. 4. Single photon device and imaging results^[33]. (a) Single photon emitter; (b) single photon cumulative imaging depth map

Fig. 5. Schematic diagram of linear structured light imaging system. (a) Principle of linear structured light scanning; (b) flow chart of structured light imaging; (c) coordinates used in structured light imaging

Fig. 6. Structure light experimental device and imaging results^[50]. (a) Diagram of line structured light equipment; (b) scan point cloud image

Fig. 7. Imaging principle of streak tube lidar. (a) Diagram of the fringe tube^[62]; (b) structure diagram of stripe-tube laser imaging radar^[63]; (c) fringe tube signal schematic diagram^[64]

Fig. 8. Airborne stripe tube equipment and imaging results^[62]. (a) Airborne stripe tube scanner; (b) three-dimensional reconstruction model of the striated tube

Fig. 9. Three-dimensional reconstruction principle of binocular camera^[75]. (a) 3D reconstruction process of binocular camera; (b) underwater binocular stereo vision model; (c) underwater binocular principle

Fig. 10. Binocular camera and its imaging results^[76]. (a) Binocular camera equipment diagram; (b) binocular camera imaging point cloud image

Fig. 11. Accuracy comparison chart of multiple underwater three-dimensional imaging methods