## 3 Results
### Further Validation of Method II  
We verified that our approach under hypothesis II also would work for other combinations of image dates by developing modified thresholds for the 26 September image based on SF relationships with the 11 July image (Table 9) and 16 August image (Table 10). Resulting modified thresholds had small differences with those of the traditional CT model for 26 September (Figure 4C) and resulted in similar maps, as well (Figure 9, and see Figure 5C for area estimates). We calculated areal extents of aquatic vegetation types in the four sections based on the maps developed for 26 September (Figure 10). Results show close agreement among three maps in total area calculated by vegetation type and sections. The greatest difference in area measurements was less than five square kilometers. We used ground-truth samples from September (sample group III) to assess user's, producer's, and overall accuracies for the maps generated for 26 September (Table 11). Overall accuracies ranged from 80% to 84%, corroborating earlier indication that the approach used for hypothesis II was effective and feasible for modifying a traditional CT model to accommodate other image dates. \begin{table}
\begin{tabular}{c c c c} \hline \hline
\begin{tabular}{c} **Region of** \\ **Interest (ROI)** \\ \end{tabular} & \(\mathbf{R^{2}}\) & **Equation** & **Modified Threshold** \\ \hline ROI 1 & 0.9444 & \(bMCT_{{}_{2-3}}^{3}\)-SF\({}_{1}^{2}\) = 1.3716\(\times TCT_{{}_{2}}\)-SF\({}_{1}^{2}\) - 0.1708 & \(bMCT_{{}_{2-3}}^{3}\)-SF\({}_{1}^{2}\) & 0.1310 \\ ROI 2 & 0.9612 & \(bMCT_{{}_{2-3}}^{3}\)-SF\({}_{2}^{2}\) = 0.8363\(\times TCT_{{}_{2}}\)-SF\({}_{2}^{2}\) - 0.0008 & \(bMCT_{{}_{2-3}}^{3}\)-SF\({}_{2}^{2}\) & \(-\)0.0677 \\ ROI 3 & 0.9796 & \(bMCT_{{}_{2-3}}^{3}\)-SF\({}_{3}^{2}\) = 0.8493\(\times TCT_{{}_{2}}\)-SF\({}_{3}^{2}\) + 0.0767 & \(bMCT_{{}_{2-3}}^{3}\)-SF\({}_{3}^{2}\) & 0.1786 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Equations and thresholds of spectral features (SFs) in a CT model for 26 September modified under hypothesis II from the traditional CT model developed for 16 August. See Table 4 for descriptions of ROIs. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
\begin{tabular}{c} **Region of** \\ **Interest (ROI)** \\ \end{tabular} & \(\mathbf{R^{2}}\) & **Equation** & **Modified Threshold** \\ \hline ROI 1 & 0.9738 & \(bMCT_{{}_{1-3}}^{3}\)-SF\({}_{1}^{2}\) = 0.6794\(\times TCT_{{}_{1}}\)-SF\({}_{1}^{2}\) + 0.1241 & \(bMCT_{{}_{1-3}}^{3}\)-SF\({}_{1}^{2}\) & 0.1581 \\ ROI 2 & 0.985 & \(bMCT_{{}_{1-3}}^{3}\)-SF\({}_{2}^{2}\) = 0.8809\(\times TCT_{{}_{1}}\)-SF\({}_{2}^{2}\) - 0.0322 & \(bMCT_{{}_{1-3}}^{3}\)-SF\({}_{2}^{2}\) & \(-\)0.0630 \\ ROI 3 & 0.9649 & \(bMCT_{{}_{1-3}}^{3}\)-SF\({}_{3}^{2}\) = 0.5353\(\times TCT_{{}_{1}}\)-SF\({}_{3}^{2}\) + 0.0715 & \(bMCT_{{}_{1-3}}^{3}\)-SF\({}_{3}^{2}\) & 0.1743 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Equations and thresholds of spectral features (SFs) in a CT model for 26 September modified under hypothesis II from the traditional CT model developed for 11 July. See Table 4 for description of ROI. See Equations (1) and (2) for definitions of mathematical terms. See Table 4 for descriptions of ROIs. Figure 10: Total area of emergent, floating-leaved and submerged vegetation in the four sections of Taihu Lake, estimated from maps developed for 26 September 2013, based on the traditional CT model for September (TCT3) and on thresholds modified from the 11 July (MCT3A) and August 16 (MCT3B) models under hypothesis II.