Reprint 776 Applications of an Infrared Doppler Lidar in Detection of Wind Shear

In December 2005, operational wind shear alerting at the Hong Kong International Airport (HKIA) reached an important milestone with the launch of the automatic Lidar (light detection and ranging) Windshear Alerting System (LIWAS). This signifies that the anemometer-based and radar-based wind shear detection technologies deployed worldwide in the twentieth century have been further advanced by the addition of the lidar—a step closer to all-weather coverage. Unlike the microburst and gust front, which have a well-defined coherent vertical structure in the lowest several hundred meters of the atmosphere, terrain-induced wind shear tends to have high spatial and temporal variability. To detect the highly changeable winds to be encountered by the aircraft under terraininduced wind shear situations, the Hong Kong Observatory devises an innovative glide path scan (GPScan) strategy for the lidar, pointing the laser beam toward the approach and departure glide paths, with the changes in azimuth and elevation angles concerted. The purpose of the GPScans is to derive the headwind profiles and hence the wind shear along the glide paths. Developed based on these GPScans, LIWAS is able to capture about 76% of the wind shear events reported by pilots over the most-used approach corridor under clear-air conditions. During the past two years, further developments of the lidar took place at HKIA, including the use of runway-specific lidar to further enhance the wind shear detection performance.