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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 10 | Copyright
Atmos. Meas. Tech., 11, 5549-5563, 2018
https://doi.org/10.5194/amt-11-5549-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Oct 2018

Research article | 12 Oct 2018

Cloud fraction determined by thermal infrared and visible all-sky cameras

Christine Aebi1,2, Julian Gröbner1, and Niklaus Kämpfer2 Christine Aebi et al.
  • 1Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Davos, Switzerland
  • 2Oeschger Center for Climate Change Research and Institute of Applied Physics, University of Bern, Bern, Switzerland

Abstract. The thermal infrared cloud camera (IRCCAM) is a prototype instrument that determines cloud fraction continuously during daytime and night-time using measurements of the absolute thermal sky radiance distributions in the 8–14µm wavelength range in conjunction with clear-sky radiative transfer modelling. Over a time period of 2 years, the fractional cloud coverage obtained by the IRCCAM is compared with two commercial cameras (Mobotix Q24M and Schreder VIS-J1006) sensitive in the visible spectrum, as well as with the automated partial cloud amount detection algorithm (APCADA) using pyrgeometer data. Over the 2-year period, the cloud fractions determined by the IRCCAM and the visible all-sky cameras are consistent to within 2oktas (0.25 cloud fraction) for 90% of the data set during the day, while for day- and night-time data the comparison with the APCADA algorithm yields an agreement of 80%. These results are independent of cloud types with the exception of thin cirrus clouds, which are not detected as consistently by the current cloud algorithm of the IRCCAM. The measured absolute sky radiance distributions also provide the potential for future applications by being combined with ancillary meteorological data from radiosondes and ceilometers.

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A newly developed hemispherical thermal infrared cloud camera (IRCCAM) is presented. The IRCCAM allows automatic cloud detection during the day and at night-time. The cloud fraction determined from the IRCCAM is compared with the cloud fraction determined from other instruments over a time period of 2 years. The IRCCAM has an agreement of +/- 2 oktas cloud fraction in 90 % of the data compared to other instruments. There are no significant differences between seasons or different times of day.
A newly developed hemispherical thermal infrared cloud camera (IRCCAM) is presented. The IRCCAM...
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