## 3 Results and Discussion  
### Overall Detection Performance Evaluation  
Given that Gonggar Airport primarily focuses on monitoring wind along the takeoff and landing direction as well as the wind perpendicular to the runway, this study conducted a statistical analysis using PPI mode data at 4\({}^{\circ}\) and 6\({}^{\circ}\) elevation angles along the runway direction (270\({}^{\circ}\) and 90\({}^{\circ}\)) and DBS mode data. Over the nine months, 443,197 scan lines in PPI mode and 177,983 in DBS mode were recorded. Overall (see Figure 2), the detection efficiency in PPI mode shows minimal attenuation from 0 to 3 km, followed by a linear decline from 3 to 6 km, after which the decrease slows. A comparison of detection efficiency across different azimuth angles reveals that the detection efficiency at the 270\({}^{\circ}\) azimuth is slightly higher than at the 90\({}^{\circ}\) azimuth, with a difference of approximately 3.2% at the 5 km mark. As shown in Figure 1a, the 270\({}^{\circ}\) azimuth points towards the river outside Gonggar Airport, while the 90\({}^{\circ}\) azimuth points towards the runway, indicating that different underlying surfaces influence the detection efficiency to some extent. When comparing the detection efficiency across different elevation angles, the 4\({}^{\circ}\) elevation outperforms the 6\({}^{\circ}\) elevation, reflecting the influence of decreasing aerosol \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Scanning type & Pulse scanning \\ Sampling rate (MHz) & 400 \\ Operating frequency range (\(\upmu\)m) & 1.55 \\ Detection range (m) & 20 to 10,000 \\ Wind speed error (\(\upmu\cdot\) s\({}^{-1}\)) & \(\leq\)0.1 \\ Wind direction error (\({}^{\circ}\)) & \(\leq\)3 \\ Minimum data refresh rate (s) & 3 \\ Wind field scanning & PPI/RHI/DBS/GLIDE \\ Data products & Wind profile (speed, direction, vertical airflow) \\ Raw data & Radial wind speed, spectral data, \\  & signal-to-noise ratio (SNR), etc. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main performance parameters of FC-III-type DWL. concentration with altitude on the PPI mode's detection efficiency. At 6 km, where the curves show noticeable variation, the 6\({}^{\circ}\) elevation scan line is approximately 210 m higher than the 4\({}^{\circ}\) elevation scan line, and the detection efficiency at the 4\({}^{\circ}\) elevation is 2.5% higher than at the 6\({}^{\circ}\) elevation. Averaging the detection efficiency across both elevation angles, the distances corresponding to 80% and 40% detection efficiencies are 3.4 km and 5.3 km, respectively. Overall, the detection efficiency in plateau regions is lower than in plains regions [15]. The 4\({}^{\circ}\) elevation angle exhibited the best performance, and lower elevation scanning modes are more advantageous during the critical stages of aircraft descent. Therefore, subsequent analysis focuses on the detection performance at the 4\({}^{\circ}\) elevation angle along the primary landing direction (270\({}^{\circ}\)). The maximum detection range along a radial line is the furthest distance at which valid data are obtained for a fixed-azimuth and -elevation-angle scan. The median and variance of the detection ranges for different azimuth angles in the PPI scans were statistically analyzed for each month, with the results presented in Table 2. Figure 2 shows that the detection range at the 90\({}^{\circ}\) azimuth angle is slightly shorter than at the 270\({}^{\circ}\) azimuth angle. In the 90\({}^{\circ}\) azimuth scans, the 5 km runway occupies a significant portion of the scan range. In contrast, the 270\({}^{\circ}\) azimuth scans primarily cover the area above the river, where the relative humidity is generally higher. Due to the hygroscopic growth effect of aerosol particles [20], the backscattering coefficient increases with higher humidity, leading to stronger echo signals and consequently better detection ranges. This suggests that variations in the underlying surface can result in differences in detection range.