A comparison between laser ceilometers at Hong Kong International Airport

摘要： The Vaisala LD12 ceilometer has been in use at the meteorological garden at Hong Kong International Airport (HKIA) since its opening in mid-1998. Another model, the LD40, was installed at the airport in the early 2000s. These instruments are mainly used for providing cloud base height measurements for reference in aviation weather reporting. The data are available on several platforms, including the aerodrome meteorological observing system and a web-based self-briefing system for pilots. Technical support for the LD12 and LD40 models is no longer provided by the manufacturer, and they are due to be replaced at HKIA by a new model with the latest laser ceilometer technology, such as the CL31. To assure continuity of cloud base height measurement, a field comparison between the LD12 and the CL31 was conducted at the meteorological garden at HKIA between July 2010 and June 2011. Another field comparison was performed between the LD40 and the CL31 over a period of 2 years from January 2016 to December 2017. In each comparison, the two ceilometers were separated by about 10m and were pointing vertically upwards without mutual interference. Photographs of the ceilometer field comparison setups are shown in Figure 1. This paper describes the analysis of the ceilometer data for the assurance of continuity of cloud base height measurements following the equipment change. It is hoped that the findings presented here might provide a useful reference for other airports implementing similar equipment replacements.