## Materials and Methods
### Experimental Region and Data
#### 2.1.3 Satellite Data  
The HJ-1 which includes three satellites (HJ-1A, HJ-1B and HJ-1C) was launched by the China Center for Resources Satellite Data and Applications (CRESDA) on 6 September 2008 ([[http://www.cresda.com/CN/](http://www.cresda.com/CN/)]([http://www.cresda.com/CN/](http://www.cresda.com/CN/))). There were two optical charge coupled devices (CCDs) and a hyper-spectrum image (HIS) loaded on HJ-1A, and there were two CCDs and an infrared scanner (IRS) on HJ-1B. HJ-1A/B had a short revisit period (two days), high spatial resolution (30 m), and large cover area (700 km), which made it applicable to monitor the regional environment. The satellite sensor parameters of HJ-1 are provided in Table 2. Considering the quality of remote sensing over the study area, the available satellite images obtained in the growth season of 2015 from April to October were selected (Table 3). All of the images were subjected to geometric correction and atmospheric correction.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Land Use** & **Site** & **Location** & **Instrument** \\ \hline Maize & Daman & 100\({}^{\circ}\)22\({}^{\prime}\)20\({}^{\prime}\) E, 38\({}^{\circ}\)51\({}^{\prime}\)20\({}^{\prime\prime}\) N & AWS, EC \\ Steppe desert & Huazhaizi & 100\({}^{\circ}\)19\({}^{\prime}\)12\({}^{\prime}\) E, 38\({}^{\circ}\)45\({}^{\prime}\)57\({}^{\prime\prime}\) N & AWS, EC \\ Desert & Gebi & 100\({}^{\circ}\)19\({}^{\prime}\)12\({}^{\prime}\) E, 38\({}^{\circ}\)45\({}^{\prime}\)57\({}^{\prime\prime}\) N & AWS \\ Desert & Shenshawo & 100\({}^{\circ}\)19\({}^{\prime}\)12\({}^{\prime}\) E, 38\({}^{\circ}\)45\({}^{\prime}\)57\({}^{\prime\prime}\) N & AWS \\ Wetland & Zhangye & 100\({}^{\circ}\)19\({}^{\prime}\)12\({}^{\prime}\) E, 38\({}^{\circ}\)45\({}^{\prime}\)57\({}^{\prime\prime}\) N & AWS \\ \hline \hline \end{tabular}
\end{table}
Table 1: Specific information for each site.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sensor** & **Band** & \begin{tabular}{c} **Spectral** \\ **Resolution** \\ **(\(\mu\)m)** \\ \end{tabular} & \begin{tabular}{c} **Spatial** \\ **Resolution** \\ **(m)** \\ \end{tabular} & **Sensor** & **Band** & \begin{tabular}{c} **Spectral** \\ **Resolution** \\ **(\(\mu\)m)** \\ \end{tabular} & **Sensation** \\ \hline HJ-1A/B CCD & \begin{tabular}{c} 1 \\ 2 \\ 3 \\ 4 \\ \end{tabular} & \begin{tabular}{c} 0.43–0.52 \\ 0.52–0.60 \\ 0.76–0.9 \\ 0.76–0.9 \\ \end{tabular} & \begin{tabular}{c} \\ 30 \\ 4 \\ \end{tabular} & \begin{tabular}{c} \\ 5 \\ 0.76–0.9 \\ \end{tabular} & \begin{tabular}{c} \\ 6 \\ 7 \\ 8 \\ \end{tabular} & \
\begin{tabular}{c} 1.55–1.75 \\ 3.5–3.9 \\ 10.5–12.5 \\ \end{tabular} &
\begin{tabular}{c} \\ 150 \\ 300 \\ 300 \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}
Table 2: HJ-1A/B charge coupled device (CCD) and HJ1-B infrared scanner (IRS) sensor parameters. HJ-1A and HJ-1B (HJ-1A/B) are the two satellites in HJ-1, respectively.  
Cropping planting structure was derived from HJ-1 CCDs data with a support vector machine (SVM), object-based method, and time-series analysis, with the overall accuracy for the crop classification reaching 84.09% [47]. The green (0.52-0.62 \(\upmu\)m), red (0.63-0.69 \(\upmu\)m), and near infrared (0.76-0.9 \(\upmu\)m) bands of HJ-1 CCDs data were used to calculate the leaf area index (LAI) through a vegetation canopy radiation model developed by [PERSON] et al. (2007) [48].