Fig. 1. Sky background radiance value at noon on a clear day

Fig. 2. Relationship between filter bandwidth and laser energy

Fig. 3. Simulated spectral diagram of a single F-P etalon combined with IF

Fig. 4. Simulated spectral diagram of double F-P etalons combined with IF

Fig. 5. Relationship between signal-to-noise R_SN and fineness F

Fig. 6. Performance evaluation function R_e varying with free spectral spacing FSR of low resolution etalon

Fig. 7. Relationship between F-P etalon transmittance curve and gas refractive index

Fig. 8. Phased control model diagram

Fig. 9. Measured transmittance curve

Fig. 10. Schematic diagram of iron resonance fluorescence lidar structure

Fig. 11. (a) Echo signals of two channels after splitting; (b) Signal-to-noise ratio of iron resonance fluorescence layer