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Evaluation of cloud base height measurements from Ceilometer CL31 and MODIS satellite over Ahmedabad, India
摘要： Clouds play a tangible role in the Earth’s atmosphere and in particular, the cloud base height (CBH), which is linked to cloud type, is one of the most important characteristics to describe the influence of clouds on the environment. In the present study, CBH observations from Ceilometer CL31 were extensively studied during May 2013 to January 2015 over Ahmedabad (23.03? N, 72.54? E), India. A detailed comparison has been performed with the use of ground-based CBH measurements from Ceilometer CL31 and CBH retrieved from MODIS (Moderate Resolution Imaging Spectroradiometer) onboard Aqua and Terra satellite. CBH retrieved from MODIS is ～ 1.955 and ～ 1.093 km on 25 July 2014 and 1 January 2015 respectively, which matches well with ceilometer-measured CBH (～ 1.92 and ～ 1.097 km). Some interesting features of cloud dynamics viz. strong downdraft and updraft have been observed over Ahmedabad which revealed different cloud characteristics during monsoon and post-monsoon periods. CBH shows seasonal variation during the Indian summer monsoon and post-monsoon period. Results indicate that the ceilometer is an excellent instrument to precisely detect low- and mid-level clouds, and the MODIS satellite provides accurate retrieval of high-level clouds over this region. The CBH algorithm used for the MODIS satellite is also able to capture the low-level clouds.
关键词： monsoon,satellite,MODIS,post-monsoon,cloud dynamics,cloud base height,ceilometer
更新于2025-09-23 15:21:21
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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