# Study of the Algorithm for Wind Shear Detection with Lidar Based on Shear Intensity Factor
## 3 Test of the Improved Algorithm Based on Numerical Simulation
### Low-Level Jet Wind Field  
A low-level jet is the strong, narrow airflow zone in the boundary layer or lower troposphere [22]. The wind speed is highest in the center of the airflow zone and lowest in the upper and lower layers, causing vertical wind speed shear. The simulated low-level jet wind field is displayed in Figure 10. To better conduct the numerical simulation  
Figure 8: The left figure is the simulated downdraft wind field in the 3-D coordinate system; the right figure is the profile view of the simulated downdraft wind field.  
Figure 9: The results of wind shear detection under the background of the downdraft wind field.  
experiments and compare the results of the three algorithms in the four wind fields, the size of the 3-D coordinate system for the space used is fixed. The simulated height of the low-level jet is higher than the actual conditions, which does not influence the experiment's purpose. Therefore, in the simulated low-level jet wind field, the maximum wind speed exists in the height range of 4000 to 5000 m, set at 40 m/s. The minimum wind speed exists at the height of 3000 m and below, at 5 m/s; the wind speed at 6000 m and above is set as 10 m/s. The red straight line in Figure 10 is the slide path and the laser beam of the simulated aircraft in slide path scanning.  
The results of wind shear detection under the background of a low-level jet wind field are shown in Figure 11, with the black dotted line representing the headwind profile data in the slide path obtained by the simulated lidar. The results reveal that the wind shear mainly exists between 5000 and 9000 m from the aircraft landing point. The algorithm WSDHP accurately identified the position of maximum wind shear, which occurred 5000 m from the aircraft landing point, and its wind shear intensity factor value was 19.69. The second maximum wind shear intensity factor was 6.2 and occurred 9000 m away from the aircraft landing point. In addition, WSDSF accurately identified the position of maximum wind shear, and its wind shear intensity factor value was 19.69, which is the same as the result of algorithm WSDHP. However, the wind shear intensity factor calculated by algorithm WSDSF at 9000 m from the aircraft landing point was 12.4, which is higher than algorithm WSDHP. Therefore, it can be further concluded that the ramp length calculated by algorithm WSDSF can more accurately identify the position of maximum wind shear and the real wind shear intensity value at each position. The double ramp detection algorithm also accurately determined the position of maximum wind shear, but it issued the false warning of wind shear near 4000 and 8000 m from the aircraft landing point, as the shear intensity values at these two positions should be significantly lower than those at 5000 and 9000 m (see the headwind profile data in the slide path). This phenomena could be because the double ramp detection algorithm is sensitive to weak wind shear.  
Figure 10: The left figure is the simulated low-level jet wind field in the 3-D coordinate system; the right figure is the profile view of the simulated low-level jet wind field.