Estimation of Global and Diffuse Photosynthetic Photon Flux Density under Various Sky Conditions Using Ground-Based Whole-Sky Images
Estimation of Global and Diffuse Photosynthetic Photon Flux Density under Various Sky Conditions Using Ground-Based Whole-Sky Images
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DOI：
10.3390/rs11080932
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发表时间：
2019-04
期刊：
影响因子：
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通讯作者：
M. Yamashita;M. Yoshimura
中科院分区：
文献类型：
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作者：
M. Yamashita;M. Yoshimura
了解光合作用光子通量密度（PPFD：μmol m−2 s−1）对于理解植物光合作用的生理过程至关重要。在短时间尺度上的全球PPFD的扩散组件是需要的光合作用的准确建模。然而，由于PPFD很难确定，它通常是从全球常规观测的入射太阳辐射（SR：W m−2）估计的。为了从SR估算PPFD，使用PAR分数（PF; PAR/SR：无单位）将光合有效辐射（PAR：W m−2）从SR中分离出来，然后使用量子能量比（Q/E：μmol J−1）将PAR转换为PPFD。在这个过程中，PF和Q/E被认为是恒定值;然而，最近有报道说，PF和Q/E在不同的天空条件下会发生变化。此外，需要漫射比（DR）来区分全球PAR中的漫射分量，并且已知DR取决于天空条件而变化。地面全天空图像可用于天空状况监测，而不是人眼判读。本研究开发了一种方法来估计全球和弥漫PPFD使用全天空图像。通过全天图像处理得到天空条件因子，并研究了这些因子对PF、总PAR和散射PAR的Q/E和DR的影响。利用不同天空条件下的天空条件因子，估算了全球和漫射PPFD的瞬时值，并在此基础上分析了天空条件因子对PF、Q/E和DR的具体影响。PPFD估计的结果具有约为+0.3%和+3.8%的小偏倚误差，全局和扩散PPFD的相对均方根误差分别约为27%和20%。
A knowledge of photosynthetic photon flux density (PPFD: μmol m−2 s−1) is crucial for understanding plant physiological processes in photosynthesis. The diffuse component of the global PPFD on a short timescale is required for the accurate modeling of photosynthesis. However, because the PPFD is difficult to determine, it is generally estimated from incident solar radiation (SR: W m−2), which is routinely observed worldwide. To estimate the PPFD from the SR, photosynthetically active radiation (PAR: W m−2) is separated from the SR using the PAR fraction (PF; PAR/SR: unitless), and the PAR is then converted into the PPFD using the quanta-to-energy ratio (Q/E: μmol J−1). In this procedure, PF and Q/E are considered constant values; however, it was reported recently that PF and Q/E vary under different sky conditions. Moreover, the diffuse ratio (DR) is needed to distinguish the diffuse component in the global PAR, and it is known that the DR varies depending on sky conditions. Ground-based whole-sky images can be used for sky-condition monitoring, instead of human-eye interpretation. This study developed a methodology for estimating the global and diffuse PPFD using whole-sky images. Sky-condition factors were derived through whole-sky image processing, and the effects of these factors on the PF, the Q/E of global and diffuse PAR, and the DR were examined. We estimated the global and diffuse PPFD with instantaneous values using the sky-condition factors under various sky conditions, based on which the detailed effects of the sky-condition factors on PF, Q/E, and DR were clarified. The results of the PPFD estimations had small bias errors of approximately +0.3% and +3.8% and relative root mean square errors of approximately 27% and 20% for the global and diffuse PPFD, respectively.