Fig. 1. Schematic of typical lidar visibility meters. (a) 905 nm portable semiconductor lidar visibility meter^[18]; (b) 3D-scanning lidar system^[21]

Fig. 2. Iteration of extinction coefficient^[17]. (a) Ierative process of extinction coefficient; (b) comparisons of visibility results by different iteration methods

Fig. 3. Flow chart of iterative inversion algorithms. (a) Fixed point iterative inversion algorithm^[19]; (b) Fernald-PSO algorithm^[23]

Fig. 4. Schematic of 1064 nm Mie-scattering lidar system^[26]

Fig. 5. Slant atmospheric optical thickness under three weather conditions^[27]. (a) Thick fog; (b) light fog; (c) haze

Fig. 6. Measurement method for slant visibility combining lidar technique with SBDART radiative transfer model^[32-33]

Fig. 7. Two-wavelength Raman-Mie scattering lidar system^[33]. (a) Configuration; (b) physical map

Fig. 8. Atmospheric scattered radiance distribution at different height layers^[34-35]. (a) 0 km; (b) 4 km; (c) 6 km; (d) 10 km

Fig. 9. Distribution of the scattered radiance^[33]. (a) Curves of scattered radiance in different directions; (b) RHI

Fig. 10. Distribution of contrast ratio between the object and the background^[33]. (a) Curves in different directions; (b) RHI

Fig. 11. Technical route for global slant visibility measurements