## 3 Results
### Classification Results and Accuracy Assessment
#### 3.3.2 Sentinel-2A Image Classification Accuracy Assessment  
The classification results of Sentinel-2A images based on the spectral model, texture model, and spectral-texture model were overlaid with the airborne image classification results, respectively, and the results are shown in Figure 6. The green zone in Figure 6 shows the cotton root rot-infested areas detected by both the airborne and Sentinel-2A images, indicating the correctly classified areas in the Sentinel-2A image. The blue zone depicts the cotton root rot-infested areas detected by the Sentinel-2A image but not detected by the airborne image, which indicates the commission area for the Sentinel-2A image. The orange zone in Figure 6 is the cotton root rot-infested areas only detected by the airborne image, which indicate the areas omitted by the Sentinel-2A image. From Table 6 and Figure 6, the classification accuracy of the spectral model, texture model, and spectral-texture model was 92.95%, 84.81%, 91.87%, respectively. The spectral model produced the highest OA to identify root rot-infested cotton, followed by the spectral-texture model and the texture model. In the classification results of the spectral model, the PA, which indicates the probability of actual areas being correctly classified, was 89.73% for the root rot category and 93.42% for the noninfested category. In other words, 89.73% (the green zones in Figure 6a) of the root rot areas were correctly identified as root rot, while 93.42% of the noninfested areas (the gray zones in Figure 6a) were correctly identified as noninfested in the classification map. Additionally, with spectral model, 10.27% of the root rot-infested areas were omitted by the Sentinel-2A image. The PA of the texture model and the spectral-texture model were 92.55% and 90.80%, respectively, for the infested category, which means that more root rot areas were identified with the texture model and the spectral-texture model. At the same time, the UA for the infested category of the texture model and the spectral-texture model was lower than that of the spectral model, indicating that more commission areas (the blue zones in Figure 6b,c) were generated from the Sentinel-2A image with the texture model and the spectral-texture model. The PA and UA for the infested category of the spectral-texture model were 90.80% and 62.70%, respectively. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{3}{*}{**Field**} & \multirow{3}{*}{
\begin{tabular}{c} **Field** \\ **Area** \\ \end{tabular} } & \multicolumn{6}{c}{**Cotton Root Rot-Infested Area**} \\ \cline{3-10}  & & \multicolumn{3}{c}{**Airborne Image**} & \multicolumn{3}{c}{**Sentinel-2A Image**} \\ \cline{3-10}  & & \multicolumn{3}{c}{**Neural Network**} & \multicolumn{3}{c}{**Spectral Model**} & \multicolumn{3}{c}{**Texture Model**} & \multicolumn{3}{c}{**Spectral-Texture Model**} \\ \cline{2-10}  & \(\mathbf{m^{2}}\) & \(\mathbf{m^{2}}\) & \% & \(\mathbf{m^{2}}\) & \% & \(\mathbf{m^{2}}\) & \% & \(\mathbf{m^{2}}\) & \% \\ \hline
1 & 628,265 & 42,548 & 6.77 & 63,919 & 10.17 & 113,130 & 18.01 & 73,327 & 11.67 \\
2 & 693,875 & 5232 & 0.75 & 1827 & 0.26 & 12,636 & 1.82 & 9730 & 1.40 \\
3 & 870,805 & 3038 & 0.35 & 3562 & 0.41 & 13,433 & 1.54 & 10,611 & 1.22 \\
4 & 929,965 & 141,717 & 15.24 & 165,906 & 17.84 & 396,430 & 42.63 & 246,838 & 26.54 \\
5 & 356,173 & 17,714 & 4.97 & 27,191 & 7.63 & 43,158 & 12.12 & 28,886 & 8.11 \\
6 & 424,042 & 187,955 & 44.32 & 261,485 & 61.66 & 318,249 & 75.05 & 243,822 & 57.50 \\
7 & 265,673 & 127,941 & 48.16 & 157,893 & 59.43 & 173,828 & 65.43 & 135,003 & 50.82 \\
8 & 189,532 & 34,141 & 18.01 & 70,841 & 37.38 & 68,155 & 35.96 & 63,212 & 33.35 \\ Total & 4,358,330 & 560,286 & 12.86 & 752,623 & 17.27 & 1,139,019 & 26.13 & 811,428 & 18.62 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Cotton root rot-infested areas of classification maps generated from airborne images and Sentinel-2A images for Fields 1–8.