Fig. 1. System layout of the up-conversion single-photon lidar

Fig. 2. (a) Continuous aerosol echo signal detection results; (b) record of factory emission during the night

Fig. 3. Comparison between the up-conversion single-photon detector(UCD) and the InGaAs APD

Fig. 4. Schematic of the frequency up-conversion Doppler wind lidar

Fig. 5. (a) Transmission and reflection curves of FPI; (b) Frequency response functions measured over nine weeks and one typical Voigt fitting curve

Fig. 6. Forty-eight-hour observation of atmospheric wind and visibility. (a) Horizontal wind speed; (b) Horizontal direction

Fig. 7. Double-edge technique that adopts: (a) a double-channel FPI; (b) a dual-frequency laser pulse

Fig. 8. One-hour observation results (a) zonal wind, (b) meridional wind, (c) horizontal wind speed, and (d) horizontal wind direction

Fig. 9. (a) Optical layout of the superconduction polarization lidar; (b) calibration layout of the lidar receiver

Fig. 10. 48 h continuous polarization lidar measurement results of (a) backscattering intensity and (b) the LDR

Fig. 11. Experimental setup (a) and photo (b) of the 1.5 μm lidar using free running InGaAs/InP SPD

Fig. 12. Range corrected signal of multi-layer clouds using the MMF receiver

Fig. 13. Single-photon distributed free-space spectroscopy. (a) Optical layout; (b) Schematic of lights propagating in the atmosphere; (c) Time sequence of the time-division multiplexing technique

Fig. 14. Backscattering signals and spectra. (a) The probe signal; (b) Reference signal without gas absorption; (c) Optical depth at different distance; (d) Lorentz fitting of the range-resolved spectrum at 4 km

Fig. 15. Results of continuous observation. (a) CO₂ concentration; (b) HDO concentration; (c) CNR; (d) Horizontal wind speed; (e) horizontal wind direction; (f) Point CO₂ detector concentration comparison

Fig. 16. (a) Optical layout of the polarization coherent Doppler lidar; (b) Optical layout of calibration

Fig. 17. Wind velocity retrieved from both S and P states backscattering by single balanced detector

Fig. 18. (a) CNR distribution of S states, (b) CNR distribution of P states and (c) distribution of depolarization ratio measured by the polarization CDL

Fig. 19. Optical layout of the coding CDWL. CW, continuous-wave laser; AOM, acoustic–optic modulator; EOM, electro-optic modulator; AWG, arbitrary waveform generator; EDFA, erbium-doped fiber amplifier; BS, beam splitter; BD, balanced detector; ADC, analog-to-digital converter

Fig. 20. Laser pulse sequence. (a) Golay coding seed laser output; (b) Amplified laser sequence without feedback control; (c) Modulated Golay coding seed laser output; (d) Amplified laser sequence output with feedback control; (e) Enlarged waveform of (d)

Fig. 21. Power spectra distribution of (a) noncoding CDWL; (b) Golay coding CDWL

Fig. 22. Identification procedure of cloud, precipitation, turbulence, and wind shear

Fig. 23. A precipitation process observed by the CDWL during 19-20 September 2019. (a) CNR; (b) Spectrum width; (c) Skewness; (d) Horizontal wind speed; (e) Horizontal wind direction; (f) Vertical wind speed; (g) log10(TKEDR); (h) Shear intensity

Fig. 24. Identification results of atmospheric conditions

Fig. 25. Comparisons of the averaged raindrop size distributions between the detection of CDL, MRR and the Parsivel-2. at 600 m Rain rates (a) RR<1 mm/h, (b) 1<RR<10 mm/h conditions

Fig. 26. Separation results of wind and rain. (a) Aerosol spectrum width; (b) Horizontal wind speed; (c) Horizontal wind direction; (d) Vertical wind speed. (e) Rain spectrum width; (f) Horizontal rain speed; (g) Horizontal rain direction; (h) Vertical rain speed