## 4 Results
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Combinations** & **R\({}^{2}\)** & **RMSE** & **MAE** \\ \hline VV-NDVI & 0.797 & 0.070 & 0.084 \\ VV-NDWI & 0.764 & 0.035 & 0.071 \\ VV-CVI & 0.862 & 0.020 & 0.043 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison results of soil moisture inversion accuracy under the three combined inversion methods of the model developed in this paper. Figure 4: Scatter plot between the measured soil moisture and simulated soil moisture in VH (**a**) and VV (**b**) polarization at C-bands using the semi-empirical model (The units of RMSE is cm\({}^{3}\)/cm\({}^{3}\)). with the slightly higher R. The results demonstrated that the proposed model could monitor soil moisture accurately using X- and C-bands SAR data in the agricultural regions. Meanwhile, the estimated accuracy of soil moisture from KOMPSAT-5 data using the proposed model was a little higher than that using [PERSON]'s model, while the result was just the opposite from Sentinel-1 data. A possible reason for this result is that the CVI in the proposed model can effectively monitor the volume scattering of vegetation canopy and improve the estimated accuracy of soil moisture using X-band SAR data. In addition, X- and C-bands SAR data were used to generate the spatial distribution of soil moisture over the three wheat fields in Figure 7. Overall, soil moisture at X- and C-bands both present uniformly distribution although they have different spatial resolutions. For Site a# and c#, the X-band has little larger values than C-band. The estimated soil moisture contents using X-band SAR data over most parts of Site c# range from 0.01 to 0.20 cm\({}^{3}\)/cm\({}^{3}\). Only small areas in the north and south of the study area have the values of above 0.30 cm\({}^{3}\)/cm\({}^{3}\). For site a#, from the values of soil moisture retrieval using X- and C- bands SAR data in Figure 7a,b, the field is relatively wetter than that in Site c# and the estimated soil moisture is above 0.20 cm\({}^{3}\)/cm\({}^{3}\). The red circle is a pond for the irrigation. For Site b#, the result from C-band has slightly higher values than X-band especially in the western regions. Thus, the proposed semi-empirical model can perform well and retrieve highly consistent soil moisture values with ground measurements. Furthermore, to further validate the effectiveness of the spatial distribution of soil moisture in Figure 7, the simulated soil moisture contents were extracted from the soil moisture maps in three sites according to their geographical information. Figure 8 shows the scatter plot of the simulated and measured soil moisture based on KOMPSAT-5 and Sentinel-1 SAR data. As shown in Figure 8, the soil moisture maps at X- and C-bands provide good spatial patterns with the ground measurements. The R at X-band is 0.791 and RMSE is 0.032 cm\({}^{3}\)/cm\({}^{3}\), which is slightly higher than that at C-band. In order to evaluate the spatial distribution of soil moisture at X- and C-bands in the same resolution, the soil moisture maps from KOMPSAT-5 SAR data were resampled to 10 m, coinciding with that from Sentinel-1 data, over the three field sites. Meanwhile, the values of soil moisture with over 0.5 cm\({}^{3}\)/cm\({}^{3}\) were eliminated so as to ensure the validity of soil moisture remote sensing monitoring. Figure 9 shows the pyramid plot of retrieved soil moisture at X- and C-bands with the same resolution of 10 m over the three field sites. The values of soil moisture were divided in 10 groups from 0 to 0.5 cm\({}^{3}\)/cm\({}^{3}\) with the interval of 0.05 cm\({}^{3}\)/cm\({}^{3}\). As can be seen from Figure 9, most of the soil moisture values are relatively compact and distributed between 0.20 and 0.25 cm\({}^{3}\)/cm\({}^{3}\) at both X- and C-bands in Site a#, while the soil moisture is between 0.10 and 0.20 cm\({}^{3}\)/cm\({}^{3}\) in Site c#. For Site b#, the soil moisture values at C-band are higher than that at X-band.