## 4 Conclusions  
Based on the data from the PPI and DBS modes of the Gonggar Airport DWL from August 2023 to April 2024, combined with manually observed data, this study provides a comprehensive evaluation of the laser radar detection performance. The evaluation includes an overall performance assessment, an analysis of monthly and daily variation characteristics, and a discussion of the relationship between meteorological factors and detection performance. The following conclusions are drawn:  
Figure 10: Scatter plots of detection ranges for the PPI mode (**a,b**) and DBS mode (**c,d**) during the period from August 2023 to April 2024, when relative humidity \(\geq\) 80%. The plots show detection ranges under non-precipitation (**a,c**) and precipitation (**b,d**) conditions. (1) The detection efficiency in plateau areas is generally lower than in plain regions. The PPI mode detection efficiency corresponds to distances of 3.4 km (80%) and 5.3 km (40%), with slight differences observed for different elevation and azimuth angles. The best detection efficiency is found at an elevation angle of 4\({}^{\circ}\) and azimuth angle of 270\({}^{\circ}\), which is beneficial for the DWL performance during the aircraft descent phase. For the DBS scanning mode, the detection efficiency corresponds to distances of 1.8 km (80%) and 2.7 km (40%), with a more pronounced attenuation rate compared to the PPI mode. (2) The detection efficiency of both the PPI and DBS modes generally showed an increasing trend throughout the experimental period. In August, the PPI mode detection efficiency at 4 km dropped below 50%, but by April, the efficiency at 7 km remained above 50%. For the DBS mode, the detection efficiency increased from above 90% at 1 km in August to over 90% at 3 km in April. Precipitation had the most significant impact on detection efficiency, and frequent low-cloud activities caused fluctuations in the detection range for the DBS mode. From February to April, the enhanced thermodynamic and dynamic effects in the lower atmosphere contributed to improved detection efficiency in the DBS mode. (3) In January, the DBS mode detection range exhibited a \"valley-peak\" daily variation pattern, possibly due to a lower boundary layer causing an increase in the PPI mode detection range. In April, the diurnal variation patterns of the DBS and PPI modes were similar to those in January, but the detection ranges were generally greater, and the diurnal variations were more pronounced. Analysis of the profiles of the DBS and PPI modes revealed that strong vertical mixing dispersed particulate matter into the upper atmosphere, improving the detection range of the DBS mode. The observed strong backscatter at altitudes below 1 km corresponded to improving the PPI mode detection range. This indicates that the increase and even distribution of lower-layer particulate matter likely contributed to the enhancement of PPI mode detection efficiency. The PPI mode was found to be more sensitive to meteorological factors, and its detection range was more easily affected by changes in atmospheric stability and particle dispersion due to thermodynamic effects and wind field variations. (4) Under low-visibility conditions, the DBS mode generally outperforms the PPI mode. When the MOR is below 4 km, the median detection range of the DBS mode is 0.2-0.6 km greater than that of the PPI mode, possibly due to the different types and sizes of aerosol particles. When relative humidity exceeds 80%, both the DBS and PPI modes show a linear decrease in detection efficiency as humidity increases. The presence of condensed water particles may contribute to the reduction in detection efficiency in high-humidity environments. At the same time, the aerosol wet deposition effect due to precipitation may further lower aerosol concentrations.