## 3 Results and Analysis  
In May 2019, we conducted a series of simultaneous observations of Lidar and UAV, and obtained eight sets of experimental data, as shown in Figure 1. Each flight takesmore than 20 min to smoothly rise by several hundred meters and approximately 10 min to descend. At the same time, three Lidar signal profiles of 355 nm were averaged for processing, with 9000 laser shots transmitted in total. In Figure 1, the black lines are the aerosol extinction coefficient profiles retrieved by Lidar, and the blue lines are the particulate mass concentration profiles measured by the UAV. Affected by the overlap factor, there is a large difference between them at low altitudes, but above 600 m, when the overlap factor approaches one, the trends of the two kinds of profiles are the same. It should be noted that the output values of the data collected by the PMS A003 miniature light scattering particle detector are named after \"PM2.5\", which is obviously not rigorous enough. However, since only the conversion relationship needs to be obtained from the acquired data, the impact of this naming is negligible. A scatter diagram of PM2.5 and extinction coefficients of the coincident profile fragments above 600 m is presented in Figure 2. The relational expression of the dot trace linear fitting is Y = 0.007056X + 0.011, and the coefficient of determination is R\({}^{2}\) = 0.988. Data from two different weather conditions are selected to calculate the overlap factors of the Lidar system. Figure 3a-c shows the analysis process of a set of data on the morning of May 13 th, local time (LT). First, the particle concentration profile is converted to the extinction coefficient profile, and the wavelet denoising process is performed [29], as shown by the blue and red lines in Figure 3a. The black line in Figure 3a is the aerosol extinction coefficient measured by Lidar. The results are more consistent at altitudes above 0.5 km, and there is a thin cloud at 0.66-0.94 km. Then, the equivalent range corrected signal is calculated from the smoothed extinction coefficient profile according to Equation (1). The red line in Figure 3b represents the range-corrected signal profile after removing the influence of the overlap factor, and the black line represents the original range-corrected signal measured by the Lidar. After adjusting the scale factor, the black line and the red line are consistent in the upper air part. After normalizing the ratio of the two range corrected profiles in Figure 3b and the upper-air part values, the overlap factor profile is obtained, as shown by the red line in Figure 3c. As a comparison, 10 sets (30,000 laser shots in all)  
Figure 1: (**a–h**) Aerosol extinction coefficient profiles measured by Lidar (black lines) and PM2.5 profiles measured by UAV (blue lines) at different times that marked in the upper right corner of each sub-figures. of 355 nm and 387 nm signals measured at 22:00 \(\sim\) 23:40 (LT) on May 11 were averaged, and the overlap factor was calculated using the Raman method. The result is shown as the black line in Figure 3c. It should be emphasized that the dramatic changes in the density of particles under the cloud make the overlap factors measured by UAV fluctuate significantly between 0.41 and 0.75 km, but the general trends of the overlap factors measured by the two methods are consistent. Figure 3d-f shows an example under clear and clean weather on the afternoon of May 20 (LT), and the content and legend are the same as those in Figure 3a-c. The results show that the overlap factors calculated by the two methods are basically the same. Due to the slight change in the direction of the emitted laser beam between the two experiments, the overlap factor slightly changes. Figure 3: Comparison of the results of calculating geometric factors by the two methods under different weather conditions: (**a–c**) thin cloud weather; (**d–f**) sunny and clean weather.