Short-term climatology and performance of lidar-based visibility map at the Hong Kong International Airport

Abstract

Visibility maps have been generated in real time at the Hong Kong International Airport (HKIA) based on the backscattered power data from Doppler light detection and ranging (lidar) systems and the visibility readings from the forward scatter sensors at the airport. The short-term climatology of visibility at HKIA (in years 2005, 2006 and 2007) is studied in this article by considering the mean visibility maps in different seasons and different years. The visibility is found to be the lowest in winter and the highest in summer. There appear to be lower visibility areas to the north through to the west of HKIA, which may be related to the haze brought about by the north to westerly winds during northeast monsoon weather in the winter and the sea breeze. The performance of the visibility map is also studied by considering the visibility maps based on the forward scatter sensors at the eastern and central parts of HKIA and using the sensors at the western part of the airport to provide independent measurements for verification purposes. Based on box plots, the visibility maps are found to have generally satisfactory quality, especially for visibility of 1500 m or above. In past studies, the lidar-based visibility map has been mostly used to study hazy and misty weather. Its performance in a fog case in 2005 is studied in the present article.