## 2 Data and Methods
### Data Processing  
#### 2.3.1 Site Data Processing  
The final data collection frequency for EC used in this study is 10 Hz, with a time output frequency of 30 min. The data collection frequency for radiation and gradient observations is 1 Hz, with a time output frequency of 30 min. All original flux observation data are initially in the TOB1 format, which can be converted to the TOB3/5 format for preliminary operations by the LoggerNet software4.0 (Campbell Scientific, Logan, UT, USA). Subsequently, EddyPro7.1 software was employed for data processing, including outlier removal [45], time lag correction [46], coordinate sequence rotation [47], frequency response correction [48], sonic virtual temperature, and density correction [49], thereby obtaining flux data with a time step of half an hour. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Product Name** & **Generation Method** & **Temporal Resolution** & **Spatial Resolution** & **Time Period** & **Acquisition Platform** \\ \hline \multirow{6}{*}{CSIF} & Based on the combination of SIF from & & & & \\  & OCO\_2 and calibrated MODIS BRDF & & & & \\  & seven-band surface reflectance, & & & & \\  & trained artificial neural networks & & & & \\  & (ANNs), applying ANNs, & & & & \\  & incorporating weather conditions, & & & & \\  & and employing machine learning & & & & \\  & algorithms to generate. & & & & \\  & Generated through machine learning & & & & \\  & reconstruction of TROPO sphere & & & & \\ RTSIF & Monitoring Instrument (TRPOMI) & & & & \\  & on Copernicus Sentinel-5P mission. & & & & \\  & Generated using & & & & \\  & data-driven methods & & & & \\  & based on SIF from OCO\_2, MODIS, & & & & \\  & and meteorological reanalysis data. & & & & \\  & Utilizes SIF from OCO\_2 and & & & & \\  & calibrated MODIS BRDF seven-band & & & & \\  & surface reflectance, trained artificial & & & & \\  & neural networks (ANNs), applying & & & & \\  & ANNs, incorporating MODIS & & & & \\  & reflectance, and land cover to predict. & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Basic information on four widely used SIF satellite products. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Name** & **Value** & **Reference** \\ \hline L & Canopy continuous & Derived from the RTSIF sensor & - \\  & radiation intensity & & \\ \(\theta\)s & Solar zenith angle & Atmospheric effects within the SIF satellite & [39] \\  & spectrum range are negligible and considered as 0 & & [40] \\ G(\(\theta\)) & Geometric mean & 0.5 & & [41; 42] \\ \(\omega\) & Absorption value of chlorophyll in the & The change in \(\omega\) in this spectrum range is minimal & [41; 42] \\  & 743–758 nm spectrum range & & and considered as a unit value of 1 & [41; 42] \\ E & Solar irradiance of & & 1277.3 mW/m\({}^{2}\)/nm & [43] \\  & 743–758 nm & & & \\ CI & Clumping index & & Determine from He L global products based on the type of underlying surface in the research area & [44] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: SIF data accuracy improvement auxiliary parameter data set. Owing to uncontrollable factors such as instrument damage and abrupt weather changes, the preliminary processed flux data may still suffer from issues, such as missing or discontinuous data. Therefore, it is necessary to further comprehensive interpolation using the [PERSON] online interpolation tool, which was performed on the half-hourly flux data. Through comprehensive processing, high-quality and continuous half-hourly flux data can be obtained. (The tool was developed by the Max Planck Institute for Biogeochemistry and can be obtained at: [[https://www.bgc-jena.mpg.de/bgi/index.php/Services/READdyProCWeb](https://www.bgc-jena.mpg.de/bgi/index.php/Services/READdyProCWeb)]([https://www.bgc-jena.mpg.de/bgi/index.php/Services/READdyProCWeb](https://www.bgc-jena.mpg.de/bgi/index.php/Services/READdyProCWeb)), accessed on 18 September 2023).