# Mapping Rice Fields in Urban Shanghai, Southeast China, Using Sentinel-1A and Landsat 8 Datasets
## 3 Results
### Mapping Results from Sentinel-1A and Landsat 8  
Results from the proposed mapping algorithm, which utilizes both the temporal VH images of Sentinel-1A and the single-date NDVI and MNDWI from Landsat 8 are presented in Figure 7.  
In Figure 7, the wide classification errors observed in Figure 6 have been reduced significantly with the introduction of single-date optical indices (NDVI and MNDWI). The map shows greater class homogeneity as much of the misclassified, island or mixed pixels have been eliminated. Rice and Water are more clearly delineated. Rice pixels can now only be seen inland, and in places where rice cultivation is most likely. The area covered by Trees has significantly reduced as a consequence of the increase in the area covered by the class \"Others\". Additionally, some of the pixels (bare surfaces, asphalt pavements, grassland, etc.) initially misclassified as Water have now been categorized into the class \"Others\". The Built category still maintains its relatively good agreement with reference data. The class accuracy assessment report of Figure 7 is given in Table 6. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Classes** & **Rice** & **Water** & **Built** & **Trees** & **Others** & **Row Total** \\ \hline Rice & 107 & 3 & 2 & 1 & 6 & 119 \\ Water & 1 & 38 & 2 & 1 & 7 & 49 \\ Built & 0 & 0 & 44 & 2 & 7 & 53 \\ Trees & 0 & 0 & 2 & 38 & 18 & 58 \\ Others & 0 & 1 & 0 & 8 & 12 & 21 \\ CT & 108 & 42 & 50 & 50 & 50 & 300 \\ PA (\%) & 99.1 & 90.5 & 88.0 & 76.0 & 24.0 & \\ UA (\%) & 89.9 & 77.6 & 83.0 & 65.5 & 57.1 & \\ Overall Classification Accuracy: 79.7\% & \multicolumn{5}{c}{Kappa Statistic: 0.73} \\ \hline \hline \end{tabular}  
* CT, PA and UA are column total, producer’s accuracy and user’s accuracy, respectively.  
\end{table} 
Table 5: Error matrix of accuracy assessment of classification with Sentinel-1A VH images. Figure 7: Simplified land-cover map of study area derived from Sentinel-1A VH and Landsat 8 OLI. In Table 6, the commission errors previously recorded in Rice have all been eliminated, with however, a few omission errors. There is a slight decrease in the accuracy of Built, but that of Water increases. The improvement in the UA of Trees corresponds to the improvement in the PA of Others. In Figures 6 and 7, it can be clearly seen that, excluding the apparent commission errors in the Rice class in Figure 6, there seems a perfect agreement on the spatial distribution of rice fields between the two maps. Paddy rice cultivation is mostly concentrated in the northeastern part of the study area, which mainly includes the urban Shanghai districts of Jiading and Baoshan. polarization exhibited the most sustained increase in backscatter of Rice A, increasing sharply from flooding/planting to apparent tillering and booting, and decreasing slightly at heading. With the VV channel, the temporal increase in backscatter saturates at the second available image for both Rice subclasses (A and B). For Rice B, even though the increase in backscatter saturates at the second image for both polarizations, the VH channel shows a relatively shallow decline compared to the steep decline at VV polarization. Using two-class separability measures reported in [51], the VH polarization is also found to have an overall better performance in discriminating the investigated land-cover classes. Hence, given its more sustained increase in temporal backscatter with rice and its better inter-class signature separability, the VH polarization was regarded optimal for our study, and whose temporal images were used in subsequent analysis. As would be expected, Water showed the lowest temporal backscatter, a feature attributable to the smooth or specular reflections from the water surface [23]. Built exhibited the highest temporal backscatter profile, which is largely ascribed to corner reflections from buildings and other vertical objects [49]. Trees also showed a high temporal backscatter profile second only to Built.