Solar-induced chlorophyll fluorescence (SIF) emissions were estimated by the "area-ratio Fraunhofer line depth (aFLD) method", a new retrieval methodology in spectra from a low spectral resolution (SR) spectroradiometer (MS-700: full width half maximum (FWHM) of 10 nm and spectral sampling interval of 3.3 nm), assisted with a scaling to reference SIF detected from high SR spectrum. The sparse pixels of a spectrum of low SR misses detecting the minimum of the O₂A absorption band around at 760 nm, which makes the SIF detection by conventional FLD methods lose accuracy considerably. To overcome this, the aFLD method uses the definite integral of spectra over a wide interval between 750 and 780 nm. The integration of the spectrum is insusceptible to the change in shape of the depression curve, leading to higher accuracy of the aFLD method. Daily SIF, calculated by the aFLD method using the spectra obtained with MS-700, was scaled to reference daily SIF calculated by the spectral fitting method using the spectra obtained from August to December 2019 with an ultrafine SR spectroradiometer (QE Pro, FWHM = 0.24 nm). As a result, SIF calculated from MS-700 spectra by aFLD method was strongly correlated with the reference SIF from QE Pro spectra (r² = 0.81) and was successfully scaled. Then, the scaled 11-year SIF from MS-700 at a deciduous broadleaf forest showed the correlation with GPP at multiple time steps: daily, monthly, and yearly, consistently during 2008–2018. The comparison of aFLD-derived SIF with the global Orbiting Carbon Observatory-2 (OCO-2) SIF data set (GOSIF) showed high correlation on monthly values during 2008–2017 (r² = 0.85). The combining approach of the aFLD method with a scaling to reference SIF successfully detected long-term canopy SIF emissions, which has great potential to provide essential information on ecosystem-level photosynthesis.

太阳诱导的叶绿素荧光 (SIF) 发射是通过“面积比弗劳恩霍夫线深度 (aFLD) 方法”估算的，这是一种新的光谱检索方法，来自低光谱分辨率 (SR) 光谱辐射计（MS-700：全宽半最大值(FWHM) 为 10 nm，光谱采样间隔为 3.3 nm)，有助于缩放到从高 SR 光谱检测到的参考 SIF。低 SR 光谱的稀疏像素未检测到 O ₂的最小值760 nm 附近的吸收带，这使得传统 FLD 方法的 SIF 检测精度大大降低。为了克服这个问题，aFLD 方法在 750 和 780 nm 之间的宽范围内使用光谱的定积分。光谱的积分不受凹陷曲线形状变化的影响，从而提高了 aFLD 方法的准确性。使用 MS-700 获得的光谱通过 aFLD 方法计算的每日 SIF 被缩放为参考每日 SIF，使用光谱拟合方法使用超细 SR 光谱仪（QE Pro，FWHM = 0.24）获得的光谱从 2019 年 8 月到 12 月纳米）。因此，通过 aFLD 方法从 MS-700 光谱计算的 SIF 与来自 QE Pro 光谱的参考 SIF ( r ² = 0.81) 并成功缩放。然后，来自落叶阔叶林 MS-700 的 11 年 SIF 显示了与 GPP 在多个时间步长的相关性：每天、每月和每年，在 2008-2018 年期间始终如一。aFLD 衍生的 SIF 与全球轨道碳观测站 2 (OCO-2) SIF 数据集 (GOSIF) 的比较显示，2008-2017 年期间的月值具有高度相关性 ( r ²  = 0.85)。aFLD 方法与参考 SIF 的缩放相结合的方法成功地检测到了长期冠层 SIF 排放，这具有提供生态系统级光合作用基本信息的巨大潜力。