# 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
### Downdraft Wind Field  
A downburst is a strong convective weather phenomenon [21]. It is a strong downdraft usually generated in thunderstorm clouds. When the aircraft passes a downburst, it will encounter a sudden change of wind direction and its altitude could drop rapidly. Therefore, it is very easy for an accident to occur when the aircraft passes a downburst. The simulated wind field of a downburst in this paper is displayed in Figure 8, where the downdraft speed and its adjacent diffusion airflow speed are both set as 50 m/s and the surrounding airflow is set as turbulent wind field. Note that the height of the simulated downdraft wind field is higher than the actual height. Since the experiment is to test the effectiveness of the improved algorithm on wind shear detection in the wind field with the characteristic of downdraft, it does not influence the experiment's purpose. The red straight line in Figure 8 is the slide path and laser beam of the simulated aircraft in slide path scanning.  
The results of wind shear detection under the background of the downdraft wind field are depicted in Figure 9, where the black dotted line represents the headwind profile data in the slide path obtained by the simulated lidar. The results revealed that wind shear exists at multiple positions. Algorithm WSDHP finds the wind shear at multiple locations. Among the results from algorithm WSDHP, the strongest wind shear is located 5000 m away from the aircraft landing point and the maximum wind shear intensity factor value is 19.35. The second-strongest wind shear is located 7000 m away from the aircraft landing point and the wind shear intensity factor value is 15.63. Algorithm WSDSF also finds wind shear at multiple locations, with the calculated maximum wind shear positions the same as the result of algorithm WSDHP. However, the calculated maximum wind shear intensity value of 55.74 is much larger than that calculated from the algorithm WSDHP. Concurrently, it is interesting that the wind shear intensity value 7000 m from the aircraft landing point is the same as that at 5000 m. In addition, both algorithms can accurately detect the position of maximum wind shear, but the maximum wind shear intensity values calculated differ due to the different ramp lengths of the two algorithms. Therefore, it can be concluded that the  
Figure 7: The results of wind shear detection under the background of the frontal wind field.  
wind shear intensity value calculated based on the ramp length from algorithm WSDSF is larger than that from algorithm WSDHP, and algorithm WSDSF can more accurately detect the position of maximum wind shear and the real wind shear intensity at each position. Concurrently, the double ramps detection algorithm also found the wind shear at multiple locations and accurately determined the location of the maximum wind shear. However, it should be noted that the wind shear intensity from the double ramp detection algorithm is much smaller than that from algorithms WSDHP and WSDSF, which did not accurately reflect the real wind shear intensity at each location. It can be concluded that the double ramp wind shear detection algorithm easily underestimated the wind shear intensity when the real wind shear was strong.