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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.
关键词： ceilometer,CL31,LD40,Hong Kong International Airport,aviation meteorology,cloud base height,LD12
更新于2025-09-11 14:15:04
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Recommendations for processing atmospheric attenuated backscatter profiles from Vaisala CL31 ceilometers
摘要： Ceilometer lidars are used for cloud base height detection, to probe aerosol layers in the atmosphere (e.g. detection of elevated layers of Saharan dust or volcanic ash), and to examine boundary layer dynamics. Sensor optics and acquisition algorithms can strongly influence the observed attenuated backscatter profiles; therefore, physical interpretation of the profiles requires careful application of corrections. This study addresses the widely deployed Vaisala CL31 ceilometer. Attenuated backscatter profiles are studied to evaluate the impact of both the hardware generation and firmware version. In response to this work and discussion within the CL31/TOPROF user community (TOPROF, European COST Action aiming to harmonise ground-based remote sensing networks across Europe), Vaisala released new firmware (versions 1.72 and 2.03) for the CL31 sensors. These firmware versions are tested against previous versions, showing that several artificial features introduced by the data processing have been removed. Hence, it is recommended to use this recent firmware for analysing attenuated backscatter profiles. To allow for consistent processing of historic data, correction procedures have been developed that account for artefacts detected in data collected with older firmware. Furthermore, a procedure is proposed to determine and account for the instrument-related background signal from electronic and optical components. This is necessary for using attenuated backscatter observations from any CL31 ceilometer. Recommendations are made for the processing of attenuated backscatter observed with Vaisala CL31 sensors, including the estimation of noise which is not provided in the standard CL31 output. After taking these aspects into account, attenuated backscatter profiles from Vaisala CL31 ceilometers are considered capable of providing valuable information for a range of applications including atmospheric boundary layer studies, detection of elevated aerosol layers, and model verification.
关键词： attenuated backscatter,aerosol layers,model verification,atmospheric boundary layer,ceilometer,Vaisala CL31,lidar
更新于2025-09-04 15:30:14