Fig. 1. Picture of SLidar system

Fig. 2. Distribution of atmospheric echo signal measured by scanning SLidar system at different time. (a) 23:07, 2021-11-29; (b) 03:32, 2021-11-30; (c) 18:50, 2021-11-30; (d) 17:35, 2021-12-01

Fig. 3. Schematic of DP algorithm

Fig. 4. Flow chart of DP algorithm

Fig. 5. Flow chart for determining boundary value by DP algorithm and retrieving extinction coefficient

Fig. 6. Results of classical DP algorithm with different threshold values. (a)-(c) Lidar signal measured at 23:07, 2021-11-29; (d)-(f) lidar signal measured at 18:50, 2021-11-30

Fig. 7. Distribution of aerosol extinction coefficient retrieved by classical DP algorithm with different threshold values. (a), (c), (e) Distribution of aerosol extinction coefficient retrieved from lidar signals measured at 23:07, 2021-11-29; (b), (d), (f) distribution of aerosol extinction coefficient retrieved from lidar signals measured at 18:50, 2021-11-30

Fig. 8. Comparisons between target signal and reference signal measured at 23:07, 2021-11-29. (a) Lidar signals of target signal and reference signal; (b) reference signal and corresponding linear region found by DP algorithm; (c) linear regions found by classical DP algorithm with different threshold values for target signal; (d) comparisons between aerosol extinction coefficient profiles of target signal and reference signal

Fig. 9. Comparisons between target signal and reference signal measured at 18:50, 2021-11-30. (a) Lidar signals of target signal and reference signal; (b) reference signal and corresponding linear region found by DP algorithm; (c) linear regions found by classical DP algorithm with different threshold values for target signal; (d) comparisons between aerosol extinction coefficient profiles of target signal and reference signal

Fig. 10. Evaluation results by classical DP algorithm for lidar signals measured at different time. (a) 07:17, 2021-12-02; (b) 22:26, 2021-12-03

Fig. 11. Comparisons between target signal and reference signal measured at 07:17, 2021-12-02. (a) Lidar signals of target signal and reference signal; (b) reference signal and corresponding linear region found by DP algorithm; (c) linear regions found by improved DP algorithm with different threshold values for target signal; (d) comparisons between aerosol extinction coefficient profiles of target signal and reference signal

Fig. 12. Comparisons between target signal and reference signal measured at 22:26, 2021-12-03. (a) Lidar signals of target signal and reference signal; (b) reference signal and corresponding linear region found by DP algorithm; (c) linear regions found by improved DP algorithm with different threshold values for target signal; (d) comparisons between aerosol extinction coefficient profiles of target signal and reference signal

Fig. 13. Comparisons between aerosol extinction coefficients retrieved by classical DP algorithm and improved DP algorithm. (a) Retrieved aerosol extinction coefficients for lidar signal measured at 23:07, 2021-11-29; (b) retrieved aerosol extinction coefficients for lidar signal measured at 18:50, 2021-11-30

Fig. 14. Distributions of extinction coefficient at different time retrieved by improved DP algorithm. (a) 23:07, 2021-11-29; (b) 03:32, 2021-11-30; (c) 18:50, 2021-11-30; (d) 17:35, 2021-12-01

Fig. 15. Comparison between measurement results obtained from SLidar technique and air-pollution monitoring station. (a) Relative humidity measured by air-pollution monitoring station; (b) comparison between aerosol extinction coefficient evaluated from SLidar technique and PM₁₀ concentration obtained from air-pollution monitoring station

Fig. 16. Scatter plot of PM₁₀ concentration and aerosol extinction coefficient under different relative humidities (RHs). (a) RH higher than or equal to 60%; (b) RH less than 60%