The shade ring correction for measurements of diffuse irradiance under clear skies |
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| Affiliation: | 1. Université de Nantes, CNRS, GEPEA, UMR-CNRS 6144, Bd de l׳Université, CRTT-BP 406, 44602 Saint-Nazaire Cedex, France;2. Mechanical and Aerospace Engineering Department, Henry Samueli School of Engineering and Applied Science, University of California, Los Angeles, CA 90095, USA;1. Key Laboratory of Special Display Technology of the Ministry of Education, National Engineering Laboratory of Special Display Technology, National key Laboratory of Advanced Display Technology, Academy of Photoelectric Technology, Hefei University of Technology, Hefei, 230009, China;2. School of Instrument Science and Opto-Electronics Engineering, Hefei University of Technology, Hefei, 230009, China;1. Max Planck Institute for Biogeochemistry, 07745 Jena, Germany;2. German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, 04103 Leipzig, Germany;3. SIMBIOS, Abertay University of Dundee, Dundee DD1 1HG, Scotland, UK;4. Institute of Environmental Sciences (CML), University Leiden, 2333CC Leiden, The Netherlands;5. Institute of Ecology, University of Innsbruck, 6020 Innsbruck, Austria;6. Systematic Botany and Functional Biodiversity Research, Institute of Biology, University of Leipzig, 04103 Leipzig, Germany;7. Department of Forest Resources, University of Minnesota, St Paul, Minnesota 55108, USA;8. Hawkesbury Institute for the Environment, University of Western Sydney, Penrith, 2751 New South Wales, Australia |
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| Abstract: | Observed and estimated values of the shade ring correction in the measurement of diffuse irradiance are compared for a sample of days which were cloud-free or almost so. Corrections are determined observationally from measurements of diffuse irradiance using both a shade ring and an occulting disc, which are recorded every minute. Estimated corrections are calculated (a) from numerical integration of analytic radiance distributions and (b) from empirical formulae. The former method gives results that are sensitive to the choice of radiance distribution. Method (b) does not account for the variation in corrections throughout the day, but is adequate for most periods. Errors due to a misalignment of the shade ring are examined, using calculations from analytic radiance distributions. |
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