Continuous All-Sky Cloud Measurements: Cloud Fraction Analysis Based on a Newly Developed Instrument
Abstract
Clouds play an important role in the climate system and are also a crucial parameter for the Earth's surface energy budget. Ground-based measurements of clouds provide data in a high temporal resolution in order to quantify its influence on radiation. The newly developed all-sky cloud camera at PMOD/WRC in Davos (Switzerland), the infrared cloud camera (IRCCAM), is a microbolometer sensitive in the 8 - 14 μm wavelength range. To get all-sky information the camera is located on top of a frame looking downward on a spherical gold-plated mirror. The IRCCAM has been measuring continuously (day and nighttime) with a time resolution of one minute in Davos since September 2015. To assess the performance of the IRCCAM, two different visible all-sky cameras (Mobotix Q24M and Schreder VIS-J1006), which can only operate during daytime, are installed in Davos. All three camera systems have different software for calculating fractional cloud coverage from images. Our study analyzes mainly the fractional cloud coverage of the IRCCAM and compares it with the fractional cloud coverage calculated from the two visible cameras. Preliminary results of the measurement accuracy of the IRCCAM compared to the visible camera indicate that 78 % of the data are within ± 1 octa and even 93 % within ± 2 octas. An uncertainty of 1-2 octas corresponds to the measurement uncertainty of human observers. Therefore, the IRCCAM shows similar performance in detection of cloud coverage as the visible cameras and the human observers, with the advantage that continuous measurements with high temporal resolution are possible.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.A53G2347A
- Keywords:
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- 0321 Cloud/radiation interaction;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0360 Radiation: transmission and scattering;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0394 Instruments and techniques;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES