Calculation of windshear hazard factor based on Doppler LIDAR data

Apart from the magnitude of headwind change, the intensity of windshear could be expressed in terms of the windshear hazard factor, which is also called the F-factor. The F-factor consists of two terms, namely, the rate of headwind change, and the vertical acceleration. An attempt is made in the present study to calculate F-factor based on the glide-path scan data of the Doppler LIDARs at the Hong Kong International Airport (HKIA). The glide-path scan of the HKIA LIDAR is designed to measure the headwind profiles along the flight paths of the airport which is then used directly to derive the headwind change term of the F-factor. The vertical acceleration term is further estimated by considering horizontal divergence based on the available LIDAR data. It is found from case studies that the vertical acceleration term does not have significant contribution to the F-factor compared to the headwind change term for the terrain-induced windshear at HKIA. The LIDAR's headwind data are then input into a B-747 simulator to calculate the F-factor profile. Case studies suggested that the LIDAR-based F-factor profile correlates reasonably well with the aircraft-based F-factor profile at the same time. The present study shows that the LIDAR-based F-factor profile could be useful in the monitoring of low-level windshear at the airport. Areas of further research for LIDAR-based F-factor would also be discussed in the paper.