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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/amt-2018-68
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
02 Mar 2018
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Measurement Techniques (AMT).
Cloud fraction determined by thermal infrared and visible all-sky cameras
Christine Aebi1,2, Julian Gröbner1, and Niklaus Kämpfer2 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 day and nighttime with high temporal resolution. It has been developed and tested at Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center (PMOD/WRC) in Davos, Switzerland. The IRCCAM consists of a commercial microbolometer camera sensitive in the 8 μm–14 μm wavelength range. Over a time period of two years, the fractional cloud coverage obtained by the IRCCAM is compared with two other commercial cameras sensitive in the visible spectrum (Mobotix Q24M and Schreder VIS-J1006) as well as with the automated partial cloud amount detection algorithm (APCADA) using pyrgeometer data. In comparison to the visible cloud detection algorithms, the IRCCAM shows median difference values of 0.01 to 0.07 cloud fraction wherein around 90 % of the data are within ±0.25 (±2 oktas) cloud fraction. Thus there is no significant difference in the cloud fraction determination of the IRCCAM in comparison to the other study instruments. Analysis indicates no significant difference in the performance of the IRCCAM during day or nighttime and also not in different seasons. The cloud types where all algorithms are in closest agreement are low-level clouds (with median differences in cloud fraction of −0.01 to 0.02), followed by mid-level (0.00) and high-level clouds (−0.13).
Citation: Aebi, C., Gröbner, J., and Kämpfer, N.: Cloud fraction determined by thermal infrared and visible all-sky cameras, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2018-68, in review, 2018.
Christine Aebi et al.
Christine Aebi et al.
Christine Aebi et al.

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Short summary
A newly developed hemispherical thermal infrared cloud camera (IRCCAM) is presented. The IRCCAM allows to detect clouds automatically during day and nighttime. The cloud fraction determined from the IRCCAM is compared with the cloud fraction determined from other instruments over a time period of two 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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