Abstract The accurate estimation of temporally-continuous gross primary production (GPP) is important for a mechanistic understanding of the global carbon budget, as well as the carbon exchange between land and atmosphere. Ground-based PhenoCams can provide near-surface observations of plant phenology with high temporal resolution and possess great potential for use in modeling the seasonal dynamics of GPP. However, due to the site-level empirical approaches for estimating the fraction of absorbed photosynthetically active radiation (fAPAR), a broad application of PhenoCams in GPP modeling has been restricted. In this study, the stage of vegetation phenology (Pscalar) is proposed, which is calculated from the excess green index (ExGI) derived from PhenoCam data. We integrate Pscalar with the enhanced vegetation index (EVI) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) in order to generate a daily time-series of the fAPAR (fAPARCAM), and then to estimate daily GPP (GPPCAM) with a light use efficiency model in a semi-arid grassland area from 2012 to 2014. Over the three continuous years, the daily fAPARCAM exhibited similar temporal behavior to the eddy covariance–measured GPP (GPPEC), and the overall determination coefficients (R2) were all > 0.81. GPPCAM agreed well with GPPEC, and these agreements were highly statistically significant (p

中文翻译：

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将 PhenoCam 衍生的植被指数整合到光利用效率模型中，以估计半干旱草原的每日初级生产总值

摘要 对时间连续性初级生产总值（GPP）的准确估计对于理解全球碳收支以及陆地和大气之间的碳交换具有重要意义。基于地面的 PhenoCams 可以提供具有高时间分辨率的植物物候的近地表观测，并且在模拟 GPP 的季节性动态方面具有巨大的潜力。然而，由于用于估计吸收的光合有效辐射 (fAPAR) 分数的站点级经验方法，PhenoCams 在 GPP 建模中的广泛应用受到限制。在本研究中，提出了植被物候阶段（Pscalar），它是根据 PhenoCam 数据得出的过量绿色指数（ExGI）计算得出的。我们将 Pscalar 与源自中分辨率成像光谱仪 (MODIS) 的增强植被指数 (EVI) 相结合，以生成 fAPAR (fAPARCAM) 的每日时间序列，然后在轻度使用情况下估计每日 GPP (GPPCAM) 2012 年至 2014 年半干旱草原地区效率模型。在连续三年中，每日 fAPARCAM 表现出与涡度协方差测量的 GPP (GPPEC) 相似的时间行为，总体决定系数 (R2) 均 > 0.81 . GPPCAM 与 GPPEC 一致，这些一致在统计上具有高度显着性（p 在连续三年中，每日 fAPARCAM 表现出与涡度协方差测量的 GPP (GPPEC) 相似的时间行为，并且总体决定系数 (R2) 均 > 0.81。GPPCAM 与 GPPEC 一致，这些一致在统计上具有高度显着性（p 在连续三年中，每日 fAPARCAM 表现出与涡度协方差测量的 GPP (GPPEC) 相似的时间行为，并且总体决定系数 (R2) 均 > 0.81。GPPCAM 与 GPPEC 一致，这些一致在统计上具有高度显着性（p