Cloud detection and classification based on MAX-DOAS observations

Atmospheric Measurement Techniques. 2014;7(5):1289-1320 DOI 10.5194/amt-7-1289-2014

 

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Journal Title: Atmospheric Measurement Techniques

ISSN: 1867-1381 (Print); 1867-8548 (Online)

Publisher: Copernicus Publications

Society/Institution: European Geosciences Union (EGU)

LCC Subject Category: Technology: Engineering (General). Civil engineering (General): Environmental engineering | Technology: Engineering (General). Civil engineering (General): Earthwork. Foundations

Country of publisher: Germany

Language of fulltext: English

Full-text formats available: PDF, XML

 

AUTHORS

T. Wagner (Max Planck Institute for Chemistry, Mainz, Germany)
A. Apituley (Royal Netherlands Meteorological Institute (KNMI), De Bilt, the Netherlands)
S. Beirle (Max Planck Institute for Chemistry, Mainz, Germany)
S. Dörner (Max Planck Institute for Chemistry, Mainz, Germany)
U. Friess (Institute for Environmental Physics, University of Heidelberg, Heidelberg, Germany)
J. Remmers (Max Planck Institute for Chemistry, Mainz, Germany)
R. Shaiganfar (Max Planck Institute for Chemistry, Mainz, Germany)

EDITORIAL INFORMATION

Peer review

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Instructions for authors

Time From Submission to Publication: 14 weeks

 

Abstract | Full Text

Multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations of aerosols and trace gases can be strongly influenced by clouds. Thus, it is important to identify clouds and characterise their properties. In this study we investigate the effects of clouds on several quantities which can be derived from MAX-DOAS observations, like radiance, the colour index (radiance ratio at two selected wavelengths), the absorption of the oxygen dimer O<sub>4</sub> and the fraction of inelastically scattered light (Ring effect). To identify clouds, these quantities can be either compared to their corresponding clear-sky reference values, or their dependencies on time or viewing direction can be analysed. From the investigation of the temporal variability the influence of clouds can be identified even for individual measurements. Based on our investigations we developed a cloud classification scheme, which can be applied in a flexible way to MAX-DOAS or zenith DOAS observations: in its simplest version, zenith observations of the colour index are used to identify the presence of clouds (or high aerosol load). In more sophisticated versions, other quantities and viewing directions are also considered, which allows subclassifications like, e.g., thin or thick clouds, or fog. We applied our cloud classification scheme to MAX-DOAS observations during the Cabauw intercomparison campaign of Nitrogen Dioxide measuring instruments (CINDI) campaign in the Netherlands in summer 2009 and found very good agreement with sky images taken from the ground and backscatter profiles from a lidar.