Abstract Predictions of hydrological states and fluxes, especially transpiration, are poorly constrained in hydrological models due to large uncertainties in parameterization and process description. Novel technologies like remote sensing of sun-induced chlorophyll fluorescence (SIF)—which provides information from the photosynthetic apparatus—may help in constraining water cycle components. This paper discusses the nature of the plant physiological basis of the fluorescence signal and analyses the current literature linking hydrological states and fluxes to SIF. Given the connection between photosynthesis and transpiration, through the water use efficiency, SIF may serve as a pertinent constraint for hydrological models. The FLuorescence EXplorer (FLEX) satellite, planned to be launched in 2023, is expected to provide spatially high-resolution measurements of red and far-red SIF complementing the products from existing satellite missions and the high-temporal resolution products from upcoming geostationary missions. This new data stream may allow us to better constrain plant transpiration, assess the impacts of water stress on plants, and infer processes occurring in the root zone through the soil-plant water column. To make optimal use of this data, progress needs to be made in 1) our process representation of spatially aggregated fluorescence signals from spaceborne SIF instruments, 2) integration of fluorescence processes in hydrological models—particularly when paired with other satellite data, 3) quantifying the impact of soil moisture on SIF across scales, and 4) assessment of the accuracy of SIF measurements—especially from space.

中文翻译：

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太阳诱导叶绿素荧光定量水文状态和通量的价值：现状和挑战

摘要 由于参数化和过程描述的巨大不确定性，水文状态和通量的预测，特别是蒸腾作用，在水文模型中的约束很差。像太阳诱导叶绿素荧光 (SIF) 遥感这样的新技术——它提供来自光合装置的信息——可能有助于限制水循环成分。本文讨论了荧光信号的植物生理基础的性质，并分析了当前将水文状态和通量与 SIF 联系起来的文献。鉴于光合作用和蒸腾作用之间的联系，通过用水效率，SIF 可以作为水文模型的相关约束。计划于 2023 年发射的荧光探索者 (FLEX) 卫星，预计将提供红色和远红色 SIF 的空间高分辨率测量，补充现有卫星任务的产品和即将到来的地球静止任务的高时间分辨率产品。这个新的数据流可以让我们更好地限制植物蒸腾作用，评估水分胁迫对植物的影响，并通过土壤-植物水柱推断根区发生的过程。为了充分利用这些数据，需要在以下方面取得进展：1) 我们对来自星载 SIF 仪器的空间聚合荧光信号的过程表示，2) 荧光过程在水文模型中的整合——特别是与其他卫星数据配对时，3) 量化土壤水分对 SIF 跨尺度的影响，以及 4) 评估 SIF 测量的准确性——尤其是从空间。