Comparison of extrapolation and interpolation methods for estimating daily photosynthetically active radiation (PAR) |
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Authors: | Guofeng Wu Jan de Leeuw Andrew K Skidmore Yaolin Liu Herbert H T Prins |
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Institution: | (1) Department of Environmental Engineering, Abant Izzet Baysal University, Bolu, Turkey;(2) Department of Farm Machinery, Faculty of Agriculture, Akdeniz University, Antalya, Turkey |
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Abstract: | Measurements of photosynthetically active radiation (PAR), which are indispensable for simulating plant growth and productivity,
are generally very scarce. This study aimed to compare two extrapolation and one interpolation methods for estimating daily
PAR reaching the earth surface within the Poyang Lake national nature reserve, China. The daily global solar radiation records
at Nanchang meteorological station and daily sunshine duration measurements at nine meteorological stations around Poyang
Lake were obtained to achieve the objective. Two extrapolation methods of PARs using recorded and estimated global solar radiation
at Nanchang station and three stations (Yongxiu, Xingzi and Duchang) near the nature reserve were carried out, respectively,
and a spatial interpolation method combining triangulated irregular network (TIN) and inverse distance weighting (IDW) was
implemented to estimate daily PAR. The performance evaluation of the three methods using the PARs measured at Dahuchi Conservation
Station (day number of measurement = 105 days) revealed that: (1) the spatial interpolation method achieved the best PAR estimation
(R
2 = 0.89, s.e. = 0.99, F = 830.02, P < 0.001); (2) the extrapolation method from Nanchang station obtained an unbiased result (R
2 = 0.88, s.e. = 0.99, F = 745.29, P < 0.001); however, (3) the extrapolation methods from Yongxiu, Xingzi and Duchang stations were not suitable for this specific
site for their biased estimations. Considering the assumptions and principles supporting the extrapolation and interpolation
methods, the authors conclude that the spatial interpolation method produces more reliable results than the extrapolation
methods and holds the greatest potential in all tested methods, and more PAR measurements should be recorded to evaluate the
seasonal, yearly and spatial stabilities of these models for their application to the whole nature reserve of Poyang Lake. |
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