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| Calibration and Validation of an All-Sky Imager |
| HUO Juan,LU Da-Ren |
| Key Laboratory for Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,Key Laboratory for Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029 |
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Abstract The automatic all-sky imager developed by the Institute of Atmospheric Physics, Chinese Academy of Sciences, provides all-sky visible images in the red, green, and blue channels. This paper presents three major calibration experiments of the all-sky imager, geometric angular calibration, optical calibration, and radiometric calibration, and then infers an algorithm to retrieve relative radiance from the all-sky images. Field experiments show that the related coefficient between retrieved radiance and measured radiance is about 0.91. It is feasible to use the algorithm to retrieve radiance from images. The paper sets up a relationship between radiance and the image, which is useful for using the all-sky image in numerical-simulations that predict more meteorological parameters.
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Received: 22 April 2009
Revised: 25 June 2009
Accepted: 27 June 2009
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