## 2 Materials and Method
### Data Acquisition
#### 2.1.2 Remote Sensing Data  
Moderate-resolution imaging spectroradiometer (MODIS) remote sensing data products are frequently used in light use efficiency models. MODIS provides high temporal resolution images of the land surface. The sensor contains 36 bands in the visible (459 nm) to thermal-infrared band (14,385 nm). Vegetation indices and land surface temperature can be retrieved from these bands. Many land surface variables products were estimated and distributed by the Land Processes Distributed Active Archive Centre (LP DAAC), and are widely used in scientific research. In this study, the 8-day land surface reflectance product (MOD09A1) and daily land surface temperature product (MOD11A1) were downloaded from the website of MODIS Land Product Subsets [21,22]. The vegetation indices (EVI and NDWI) were estimated from the MOD09A1. MOD09A1 data were resampled to 1 km spatial resolution. The temporal profiles of the vegetation indices and LST were extracted according to the geographical coordinates of the two stations. The vegetation indices were smoothed using the Savizky-Golay algorithm [23] and were interpolated into daily data.  
The formulas for EVI, NDWI and the Savizky-Golay algorithm are as follows:  
\[EVI=G\times\left(\rho_{air}-\rho_{rad}\right)/\left(\rho_{air}+\left(C_{1} \times\rho_{rad}-C_{2}\times\rho_{blue}\right)+\mathrm{L}\right) \tag{1}\]  
\begin{table}
\begin{tabular}{c c c} \hline
**Measurements** & **Daman Superstation** & **Zhangye wetland Station** \\ \hline Location & 100.3722\({}^{\circ}\) E, 38.8555\({}^{\circ}\) N & 100.4464\({}^{\circ}\) E, 38.9751\({}^{\circ}\) N \\ Elevation & 1556.06 m & 1460.00 m \\ Land cover & Maize & Reed \\ Wind speed & 3 m, 5 m, 10 m, 15 m, & 5 m and 10 m \\  & 20 m, 30 m and 40 m & \\  & 3 m, 5 m, 10 m, 15 m, & \\ Wind direction & 20 m, 30 m and 40 m & 10 m \\  & 3 m, 5 m, 10 m, 15 m, & \\ Air temperature, relative humidity & 20 m, 30 m and 40 m & 5 m and 10 m \\  & 3 m, 5 m, 10 m, 15 m, & \\ CO\({}_{2}\) concentration & 20 m, 30 m and 40 m & No measurement \\ Air pressure & 2 m & 2 m \\ Land surface temperature & 12 m & \\ PAR & 12 m & 6 m \\ Soil heat flux & 6 cm & 6 cm \\  & 0 cm, 2 cm, 4 cm, 10 cm, 20 cm, & 0 cm, 2 cm, 4 cm, \\ Soil temperature & 40 cm, 80 cm, 120 cm and 160 cm & 10 cm, 20 cm and 40 cm \\  & 2 cm, 4 cm, 10 cm, 20 cm, 40 cm, & No measurement \\ Soil moisture & 80 cm, 120 cm and 160 cm & \\ Rainfall & 2.5 m & 10 m \\ EC systems & 4.5 m & 5.2 m \\ \hline \end{tabular}
\end{table}
Table 1: Observing items at the Daman superstation and Zhangye wetland station.  
_Remote Sens._**2015**, \(7\)  
\[NDWI=\frac{\rho_{air}-\rho_{air}}{\rho_{air}+\rho_{air}} \tag{2}\]  
\[Y_{i}^{*}=\frac{1}{2m+1}\sum\
olimits_{j=-m}^{j=n}C_{j}Y_{i+j} \tag{3}\]  
where \(G\) is 2.5, _C1_ is 6, _C2_ is 7.5 and \(L\) is 1, _phae, pred_, _phir_ and _phir_ are the reflectance of the blue (band 4), red (band 1), near infrared (band 2) and shortwave infrared bands (band 6), \(Y\) is the original time-series data, _Y_\({}_{i}^{*}\) is the reconstructed time-series data, _Cj_ is the jth weight of the filter window and 2 m + 1 is the size of the filter window. The window size and order of Savizky-Golay algorithm were set to 13 and 4 based on previous studies [24,25].