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Cloud screening and quality control algorithm for star photometer data: assessment with lidar measurements and with all-sky-images

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Author(s): D. Pérez-Ramírez | H. Lyamani | F. J. Olmo | D. N. Whiteman | F. Navas-Guzman | L. Alados-Arboledas

Journal: Atmospheric Measurement Techniques Discussions
ISSN 1867-8610

Volume: 5;
Issue: 1;
Start page: 1657;
Date: 2012;
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ABSTRACT
This paper present the development and set up of a cloud screening and data quality control algorithm for a star photometer based on CCD camera as detector. This kind of algorithms is necessary for passive remote sensing techniques to retrieve the columnar aerosol optical depth, δAe(λ), and precipitable water vapor content, W, at night-time. This cloud screening procedure consists of calculating moving averages of δAe(λ) and W under different time-windows combined with a procedure for detecting outliers. Additionally, to avoid undesirable δAe(λ) and W fluctuations caused by the atmospheric turbulence, the data are averaged on 30 min. The algorithm is applied to the star photometer deployed in the city of Granada (37.16° N, 3.60° W, 680 m a.s.l.; South-East of Spain) for the measurements acquired between March 2007 and September 2009. The algorithm is evaluated with correlative measurements registered by a lidar system and also with all-sky images obtained at the sunset and sunrise of the previous and following days. Promising results are obtained detecting cloud-affected data. Additionally, the cloud screening algorithm has been evaluated under different aerosol conditions including Saharan dust intrusion, biomass burning and pollution events.
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