## 4 Results
### Relationship between ET Estimates and Land Use Status  
Since spatial distributions of ET estimates were obtained (Figure 3), we can conduct deep analyses by combining the land use types (Figure 1). The land use type within the study area, which was based on the aerial remote sensing data of the Compact Airborne Spectrographic Imager (CASI) and used the Support Vector Machine (SVM) for classification, was also provided by the Heihe Plan Science Data Center [39].  
There were five land uses types in the study area, including maize growing, village habitats, vegetable crops, orchards and woodlands. For each land use type, we performed statistical computation and gave an average ET. Table 3 shows the average ET of each land use type on the three days. Maize had the maximum ET, and the average ETs on the three days were 528 W/m\({}^{2}\), 389 W/m\({}^{2}\) and 425 W/m\({}^{2}\), respectively. Vegetable crops, orchards and woodlands had an average ET between 400 W/m\({}^{2}\) and 500 W/m\({}^{2}\) on 10 July and an average ET of approximately 300 W/m\({}^{2}\) on the other two days. Villages showed the lowest ET, with an average value of 330 W/m\({}^{2}\) on 10 July and less than 200 W/m\({}^{2}\) on the other two days. The spatial distribution of ET was intimately linked with vegetation patterns. In general, high ET is in accordance with dense vegetation cover, whereas low ET agrees with sparse vegetation cover. It indicates that the SEB-A method can well demonstrate ET differences caused by land use types. This agrees with previous suggestions that estimating ET at a regional level requires the incorporation of heterogeneous surface conditions [40]. We used the normalized difference vegetation index (NDVI) as an indicator to describe the vegetation characterization and gave phenology of maize, which is the staple crop in the study area. The summarized NDVIs of maize, vegetables, orchards and woodland, and the phenology of maize, are shown in Tables 4 and 5, respectively. In July and August, maize is in its vigorous growth season (Table 5) with frequent irrigation, and hence, the vegetation cover (Table 4) is dense and the ET is high. Because the orchards, vegetation (pepper, celery and cauliflower) and woodlands had sparse vegetation cover compared to the maize during this time, their associated ETs are lower than those of maize. As for villages, they had largely bare and solidified underlying surfaces, and thus their ETs were the lowest. These results are consistent with the facts.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Land Use Type**} & \multicolumn{2}{c}{**10 July (W/m\({}^{2}\))**} & \multicolumn{2}{c}{**11 August (W/m\({}^{2}\))**} & \multicolumn{2}{c}{**27 August (W/m\({}^{2}\))**} \\ \cline{2-7}  & \(\mathbf{LE_{act}}\) & \(\mathbf{LE_{exo}}\) & \(\mathbf{LE_{act}}\) & \(\mathbf{LE_{exo}}\) & \(\mathbf{LE_{act}}\) & \(\mathbf{LE_{exo}}\) \\ \hline maize & 528 & 91 & 389 & 36 & 425 & 71 \\ vegetable & 410 & \(-\)18 & 304 & 23 & 268 & 0 \\ orchard & 506 & 66 & 292 & \(-\)35 & 302 & \(-\)63 \\ woodland & 461 & 53 & 300 & \(-\)46 & 246 & 27 \\ village & 330 & \(-\)32 & 177 & 0 & 186 & 22 \\ \hline \hline \end{tabular}
\end{table}
Table 3: ET estimates and the exotic ET retrieved by the SEB-A method on five different land use types on 10 July, 11 August and 27 August 2012.  
Figure 5: The frequency distribution of percent errors on ET estimates.