Fig. 1. Monthly averaged atmospheric temperature distribution with height. (a) 0000UTC；(b) 1200UTC

Fig. 2. Monthly averaged atmospheric humidity distribution with height. (a) 0000UTC；(b) 1200UTC

Fig. 3. Distribution at 0000UTC、1200UTC in Jan, Apr, Jul, Oct with height. (a) Atmospheric temperature; (b) atmospheric humidity

Fig. 4. Monthly distribution of transmittance of 3-5 μm under the path with height of 800 m, distance of 3000 m and pitch of 30°

Fig. 5. Monthly distribution of transmittance of 8-12 μm under the path with height of 800 m, distance of 3000 m and pitch of 30°

Fig. 6. Monthly distribution of transmittance of 3-5 μm under the path with height of 3500 m, distance of 3000 m and pitch of -50°

Fig. 7. Monthly distribution of transmittance of 8-12 μm under the path with height of 3500 m, distance of 3000 m and pitch of -50°

Fig. 8. Distribution of transmittance at 0000UTC、1200UTC in Jan, Apr, Jul, Oct of 3-5 μm、8-12 μm under the path with height of 800 m, distance of 3000 m and pitch of 30°

Fig. 9. Variation of transmittance with wavelength and height at 0000UTC in Jan.（a）3-5 μm；（b）8-12 μm

Fig. 10. Distribution of transmittance at 0000UTC in Jan, Apr, Jul, Oct of 3-5 μm、8-12 μm under the low cloud and the path with height of 1500 m, distance of 3000 m and pitch of 30°

Fig. 11. Distribution of transmittance at 0000UTC in Jan, Apr, Jul, Oct of 3-5 μm、8-12 μm under the low cloud and the path with height of 4000 m, distance of 3000 m and pitch of -50°