Solar-Induced Chlorophyll Fluorescence (SIF) is an emission of light in the 650–850 nm spectral range from the excited state of the chlorophyll-a pigment after absorption of photosynthetically active radiation (PAR). As this is directly linked to the electron transport chain in oxygenic photosynthesis, SIF is a powerful proxy for photosynthetic activity. SIF observations are relatively new and, while global scale measurements from satellites using high-resolution spectroscopy of Fraunhofer bands are becoming more available, observations at the intermediate canopy scale using these techniques are sparse. We present a novel ground-based spectrometer system - PhotoSpec - for measuring SIF in the red (670–732 nm) and far-red (729–784 nm) wavelength range as well as canopy reflectance (400–900 nm) to calculate vegetation indices, such as the normalized difference vegetation index (NDVI), the enhanced vegetation index (EVI), and the photochemical reflectance index (PRI). PhotoSpec includes a 2D scanning telescope unit which can be pointed to any location in a canopy with a narrow field of view (FOV = 0.7°). PhotoSpec has a high signal-to-noise ratio and spectral resolution, which allows high precision solar Fraunhofer line retrievals over the entire fluorescence wavelength range under all atmospheric conditions using a new two-step linearized least-squares retrieval procedure. Initial PhotoSpec observations include the diurnal SIF cycle of single broad leaves, grass, and dark-light transitions. Results from the first tower-based measurements in Costa Rica show that the instrument can continuously monitor SIF of several tropical species throughout the day. The PhotoSpec instrument can be used to explore the relationship between SIF, photosynthetic efficiencies, Gross Primary Productivity (GPP), and the impact of canopy radiative transfer, viewing geometry, and stress conditions at the canopy scale.

中文翻译：

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PhotoSpec：一种测量空间分布的红色和远红色太阳诱导叶绿素荧光的新仪器

太阳诱导的叶绿素荧光 (SIF) 是在吸收光合有效辐射 (PAR) 后叶绿素 a 色素激发态发出的 650-850 nm 光谱范围内的光。由于这与含氧光合作用中的电子传递链直接相关，因此 SIF 是光合作用活动的有力代表。SIF 观测相对较新，虽然使用弗劳恩霍夫波段高分辨率光谱从卫星进行的全球尺度测量变得越来越可用，但使用这些技术在中间冠层尺度上进行的观测却很少。我们提出了一种新型地面光谱仪系统 - PhotoSpec - 用于测量红色 (670–732 nm) 和远红色 (729–784 nm) 波长范围内的 SIF 以及冠层反射率 (400–900 nm) 以计算植被指数，如归一化植被指数（NDVI）、增强植被指数（EVI）和光化学反射指数（PRI）。PhotoSpec 包括一个 2D 扫描望远镜单元，该单元可以指向具有狭窄视野 (FOV = 0.7°) 的树冠中的任何位置。PhotoSpec 具有高信噪比和光谱分辨率，允许在所有大气条件下使用新的两步线性化最小二乘检索程序在整个荧光波长范围内进行高精度太阳弗劳恩霍夫谱线检索。最初的 PhotoSpec 观测包括单片阔叶、草和暗光过渡的昼夜 SIF 循环。哥斯达黎加首次基于塔的测量结果表明，该仪器可以全天连续监测几种热带物种的 SIF。