Long-term comparisons of net radiation calculation schemes |
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Authors: | J H Kjaersgaard R H Cuenca F L Plauborg S Hansen |
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Affiliation: | 1.Department of Agricultural Sciences,The Royal Veterinary and Agricultural University,Taastrup,Denmark;2.Department of Biological and Ecological Engineering,Oregon State University,Corvallis,USA;3.Department of Agroecology, Danish Institute of Agricultural Sciences,Research Centre Foulum,Tjele,Denmark |
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Abstract: | Six commonly used models for calculating daily net radiation were tested against measured net radiation. Meteorological data
from 32 and 7 consecutive years obtained at two temperate sites were used. The extensive duration of the datasets ensured
that all weather conditions and extreme events were captured. A set of statistical procedures was used to evaluate the performance
of the models. The mean bias errors ranged from 0.0 W m−2 to 24.8 W m−2 and 0.1–24.7 W m−2 and root mean square error from 11.0 W m−2 to 28.1 W m−2 and 10.0–27.9 W m−2 at the two sites respectively, for days without snow cover on the ground. The best agreement was found when locally calibrated
model coefficients were used. Only negligible differences in model performances were found between the two sites and the differences
were lower than the inaccuracies of the net radiation instruments used. Including days with snow cover in the analysis lead
to a slight increase in the bias and scatter of the predictions. Model performances were in general better during summertime
than wintertime. Altered albedo values during winter caused by generally low sun angles were likely the cause of this. Analysis
showed that at least 5 years of data were needed to obtain stable calibration coefficients for local calibration of the models.
Based on the results from this study, and due to their physical background, two physical based models were recommended for
calculating daily values of net radiation under temperate climate regimes. A simple adjustment of the calibration coefficients
based on climate regime was suggested for these models. |
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Keywords: | Albedo Net Radiation Prediction Surface radiation balance Temperate climate regime |
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