Fig. 1. Composition of underwater 3D imaging extended range lidar

Fig. 2. Waveform of laser output

Fig. 3. Results of three filtering methods. (a) Mean filtering; (b) Mean filtering+ K-nearest neighbor smoothing filtering; (c) Mean filtering+ neighborhood average filtering

Fig. 4. Resolution target

Fig. 5. Imaging results at 20 meters in clear water environment. (a) 3D image; (b) Intensity image

Fig. 6. Statistical result and imaging result at 20 meters in clear water environment. (a) Statistical result; (b) 3D image

Fig. 7. Gain of different attenuation coefficients

Fig. 8. Intensity profiles at 5.9 m and 10.7 m in turbid water. (a) Intensity image without band-pass filter (5.9 m); (b) Intensity image with band-pass filter (10.7 m)

Fig. 9. Imaging result of target and iron plate

Fig. 10. Imaging results at 13 m in clear water environment. (a) 3D image; (b) Intensity image

Fig. 11. Imaging accuracy of target in clear water