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A New Clear-Sky Method for Assessing Photosynthetically Active Radiation at the Surface Level

1
Finnish Meteorological Institute, 70211 Kuopio, Finland
2
MINES ParisTech, PSL Research University, Centre Observation, Impacts, Energy, 06904 Sophia Antipolis, France
3
NOAA Earth System Research Laboratory, Global Monitoring Division (GMD), Boulder, CO 80305, USA
*
Author to whom correspondence should be addressed.
Atmosphere 2019, 10(4), 219; https://doi.org/10.3390/atmos10040219
Received: 1 April 2019 / Revised: 16 April 2019 / Accepted: 18 April 2019 / Published: 23 April 2019
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Abstract

A clear–sky method to estimate the photosynthetically active radiation (PAR) at the surface level in cloudless atmospheres is presented and validated. It uses a fast and accurate approximation adopted in several radiative transfer models, known as the k-distribution method and the correlated-k approximation, which gives a set of fluxes accumulated over 32 established wavelength intervals. A resampling technique, followed by a summation, are applied over the wavelength range [0.4, 0.7] µm in order to retrieve the PAR fluxes. The method uses as inputs the total column contents of ozone and water vapor, and optical properties of aerosols provided by the Copernicus Atmosphere Monitoring Service. To validate the method, its outcomes were compared to instantaneous global photosynthetic photon flux density (PPFD) measurements acquired at seven experimental sites of the Surface Radiation Budget Network (SURFRAD) located in various climates in the USA. The bias lies in the interval [−12, 61] µmol m−2 s−1 ([−1, 5] % in values relative to the means of the measurements at each station). The root mean square error ranges between 37 µmol m−2 s−1 (3%) and 82 µmol m−2 s−1 (6%). The squared correlation coefficient fluctuates from 0.97 to 0.99. This comparison demonstrates the high level of accuracy of the presented method, which offers an accurate estimate of PAR fluxes in cloudless atmospheres at high spatial and temporal resolutions useful for several bio geophysical models. View Full-Text
Keywords: photosynthetically active radiation; correlated–k approximation; resampling technique; Copernicus Atmosphere Monitoring Service; cloudless atmospheres; albedo photosynthetically active radiation; correlated–k approximation; resampling technique; Copernicus Atmosphere Monitoring Service; cloudless atmospheres; albedo
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Wandji Nyamsi, W.; Blanc, P.; Augustine, J.A.; Arola, A.; Wald, L. A New Clear-Sky Method for Assessing Photosynthetically Active Radiation at the Surface Level. Atmosphere 2019, 10, 219.

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