Fig. 1. Effective backscatter cross section for the 1083 nm lines

Fig. 2. Saturation absorption spectrum of metastable Helium

Fig. 3. Density distribution model of metastable Helium

Fig. 4. Pulsed lidar system schematic

Fig. 5. Telescope beam path

Fig. 6. Combined transmission curve of FPI filter and interference filter

Fig. 7. Simulated receiving signal of pulsed lidar

Fig. 8. Simulated SNR of pulsed lidar

Fig. 9. Bistatic schematic of continuous lidar

Fig. 10. Continuous lidar system schematic

Fig. 11. FADOF schematic

Fig. 12. Combined transmission curve of FADOF and interference filter

Fig. 13. Simulated receiving signal of continuous lidar

Fig. 14. Simulated SNR of continuous lidar

Fig. 15. Simulated SNR of continuous lidar (range resolution is 50 km)

Fig. 16. Comparison of SNR between pulsed lidar and continuous lidar(W and S stand for winter and summer respectively, P and C stand for pulsed lidar and continuous lidar respectively)