## 3 Methods  
The technical route for this study encompassed the four main aspects illustrated in Figure 3: (1) Data Acquisition, which involves obtaining remote-sensing data, meteorological data, validation data, and other relevant data sources; (2) Construction of the kernel  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Station Name** & **Longitude (\({}^{\circ}\))** & **Latitude (\({}^{\circ}\))** & **Vegetation Type** \\ \hline Changbaishan & 128.096 & 42.402 & Forest \\ Qianyanzhou & 115.063 & 26.747 & Forest \\ Dinghushan & 112.536 & 23.173 & Forest \\ Xishuangbanna & 101.266 & 21.950 & Forest \\ Haibei & 101.331 & 37.665 & Shrub \\ Dang Xiong & 91.066 & 30.497 & Grassland \\ Inner Mongolia & 116.675 & 43.545 & Grassland \\ Yucheng & 116.640 & 36.958 & Farmland \\ \hline \hline \end{tabular}
\end{table}
Table 2: Details of the observation stations of carbon flux.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Data Types** & **Data Sources** \\ \hline vegetation type & [[https://doi.org/10.5067/MODIS/MCD12Q1.006](https://doi.org/10.5067/MODIS/MCD12Q1.006)]([https://doi.org/10.5067/MODIS/MCD12Q1.006](https://doi.org/10.5067/MODIS/MCD12Q1.006)) (accessed on 10 August 2022) \\ NDVI & [[http://www.vito-eodata.be](http://www.vito-eodata.be)]([http://www.vito-eodata.be](http://www.vito-eodata.be)) (accessed on 6 June 2022) \\ temperature & [[http://www.geodata.cn](http://www.geodata.cn)]([http://www.geodata.cn](http://www.geodata.cn)) (accessed on 2 September 2022) \\ precipitation & [[http://www.geodata.cn](http://www.geodata.cn)]([http://www.geodata.cn](http://www.geodata.cn)) (accessed on 2 September 2022) \\ evaporation & [[http://www.geodata.cn](http://www.geodata.cn)]([http://www.geodata.cn](http://www.geodata.cn)) (accessed on 2 September 2022) \\ radiation & [[https://doi.org/10.24381/cds.68d2](https://doi.org/10.24381/cds.68d2) bb30]([https://doi.org/10.24381/cds.68d2](https://doi.org/10.24381/cds.68d2) bb30) (accessed on 30 August 2022) \\ carbon flux & [[http://www.crem.org.cn](http://www.crem.org.cn)]([http://www.crem.org.cn](http://www.crem.org.cn)) (accessed on 30 October 2022) \\ MOD17A3 HGF & [[https://doi.org/10.5067/MODIS/MOD17A3](https://doi.org/10.5067/MODIS/MOD17A3) HGF.061]([https://doi.org/10.5067/MODIS/MOD17A3](https://doi.org/10.5067/MODIS/MOD17A3) HGF.061) (accessed on 30 October 2022) \\ ChinaNPP_1985_2015 & [[http://www.geododata.cn/](http://www.geododata.cn/)]([http://www.geododata.cn/](http://www.geododata.cn/)) (accessed on 30 October 2022) \\ GLO-PEM NPP & [[https://www.resdc.cn/](https://www.resdc.cn/)]([https://www.resdc.cn/](https://www.resdc.cn/)) (accessed on 30 October 2022) \\ administrative divisions & [[http://ngcc.bssm.gov.cn/](http://ngcc.bssm.gov.cn/)]([http://ngcc.bssm.gov.cn/](http://ngcc.bssm.gov.cn/)) (accessed on 15 June 2022) \\ soil & [[http://dx.doi.org/10.3334/ORNLDAAC/1247](http://dx.doi.org/10.3334/ORNLDAAC/1247)]([http://dx.doi.org/10.3334/ORNLDAAC/1247](http://dx.doi.org/10.3334/ORNLDAAC/1247)) (accessed on 19 September 2022) \\ GDP & [[https://www.resdc.cn/](https://www.resdc.cn/)]([https://www.resdc.cn/](https://www.resdc.cn/)) (accessed on 19 September 2022) \\ population & [[https://www.resdc.cn/](https://www.resdc.cn/)]([https://www.resdc.cn/](https://www.resdc.cn/)) (accessed on 19 September 2022) \\ DEM & [[http://www.gscloud.cn/](http://www.gscloud.cn/)]([http://www.gscloud.cn/](http://www.gscloud.cn/)) (accessed on 15 June 2022) \\ \hline \hline \end{tabular}
\end{table}
Table 3: The datasets used in this paper.  
function by referencing the RBF algorithm in machine learning to optimize the normalized vegetation index NDVI; (3) Estimation and Accuracy Validation of the net primary productivity (NPP) utilizing the CASA model to estimate vegetation NPP in Chinese terrestrial ecosystems in the past two decades and validating the results using the validation data; and (4) Analysis of the spatiotemporal evolution of NPP, including trend analysis and examination of the driving mechanisms.