## 3 Methodology
### Stability and Sensitivity  
The land surface water extraction results of the eight test points based on SMDPSO+LFE are shown in Figure 14.  
The OA and Kappa coefficients of the eight test areas are shown in Table 4.  
Figure 14: Global stability test sample: (**a**) Mountain lakes in Thailand; (**b**) Lake Gandhi in India; (**c**) Aral Sea in Kazakhstan; (**d**) Nasser reservoir in Egypt; (**e**) Congo river; (**f**) Magdalena river in Colombia; (**g**) Mexican coastal lake; (**h**) Mississippi River in the United States.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Single-Band** & **Water Index** & **Decision Tree** & \
\begin{tabular}{c} **Supervised** \\ **Classification** \\ \end{tabular} &
\begin{tabular}{c} **Unsupervised** \\ **Classification** \\ \end{tabular} & **SMDPSO** & **SMDPSO+LFE** \\ \hline
**OA** & 93.38\% & 93.32\% & 93.38\% & 93.79\% & 94.67\% & 96.02\% & 97.56\% \\ \hline
**Kappa** & 0.84 & 0.84 & 0.87 & 0.88 & 0.89 & 0.91 & 0.95 \\ \hline
**f1** & 90.77\% & 90.56\% & 92.43\% & 91.87\% & 95.24\% & 96.54\% & 96.99\% \\ \hline
_miou_ & 86.65\% & 86.46\% & 87.96\% & 87.20\% & 89.75\% & 92.19\% & 95.17\% \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison results of the coefficients of extraction using different methods.  
Three sampling areas were selected to evaluate the sensitivity of SMDPSO+LFE to the standard water spectrum. The standard water spectrum vector values of the different areas applied to water probability are shown in Table 5 below.  
The overall classification accuracy of SMDPSO+LFE using different standard water spectral values is shown in Figure 15. Lake Superior has a relatively high OA value in the study area and the eight stability test areas.  
In this study, the size of the block in the study area of Poyang Lake changed from 3 to 10 were used to extract surface water separately, and the corresponding OA was calculated according to the sampling results, as shown in Table 6.  
In this paper, different iterations were used to output the image water extraction results from the images in the research area, the OA and Kappa coefficients were calculated for the water extraction results.  
The number of iterations and the relationship between the OA and Kappa coefficients are shown in Figure 16.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Block Size** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** \\ \hline
**OA** & 97.33\% & 97.64\% & 97.66\% & 97.39\% & 96.94\% & 95.59\% & 93.61\% & 93.00\% \\ \hline \hline \end{tabular}
\end{table}
Table 6: Overall classification accuracy of different block sizes.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Blue** & **Green** & **Red** & **Nir** & **NDVI** \\ \hline
**Lake Superior** & 0.0745 & 0.0403 & 0.0240 & 0.0173 & 0.8521 \\
**Congo river** & 0.1167 & 0.0837 & 0.6320 & 0.5500 & 0.6294 \\
**Persian Gulf** & 0.1058 & 0.0858 & 0.6230 & 0.5090 & 0.7098 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison of the results for the coefficients of extraction using different methods.  
Figure 15: The overall classification accuracy of the water spectrum based on different standards.