## 4 Results
### Soil Salinity Prediction and Accuracy Assessment
#### 4.4.3 Soil Salinity Prediction and Accuracy Assessment Using OCK Method  
Spatial distribution maps of soil salinity prediction of two measuring modes using OCK with covariable factor, soil moisture content, and the defined parameters on semi-variogram modeling and standard searching neighborhood are displayed in Figure 11.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Sub-District**} & \multicolumn{4}{c}{**ECe of HH in mS/m**} & \multicolumn{4}{c}{**ECe of VV in mS/m**} \\ \cline{3-8}  & & **Mean** & **SD** & **CV (\%)** & **Mean** & **SD** & **CV (\%)** \\ \hline
1 & [PERSON] & 1129.58 & 157.12 & 13.91 & 1667.88 & 115.04 & 6.90 \\
2 & [PERSON] & 970.15 & 237.47 & 24.48 & 1425.91 & 274.72 & 19.27 \\
3 & [PERSON] & 1112.86 & 601.44 & 54.04 & 1583.40 & 507.65 & 32.06 \\
4 & [PERSON] & 2556.93 & 2264.80 & 88.57 & 2322.46 & 1471.11 & 63.34 \\
5 & [PERSON] & 2514.55 & 1944.74 & 77.34 & 2634.56 & 1363.22 & 51.74 \\
6 & Banlang & 558.35 & 410.09 & 73.45 & 1044.08 & 625.42 & 59.90 \\
7 & [PERSON] & 3254.51 & 1113.11 & 34.20 & 3034.58 & 728.46 & 24.01 \\
8 & Khang Phlu & 6121.94 & 2119.35 & 34.62 & 4973.25 & 1157.16 & 23.27 \\
9 & Samrong & 2011.21 & 1307.49 & 65.01 & 2400.37 & 957.45 & 39.89 \\
10 & Kampang & 2040.13 & 650.99 & 31.91 & 2607.17 & 628.83 & 24.12 \\ \hline
**Non Thai District** & **2291.19** & **1944.79** & **84.88** & **2401.41** & **1338.30** & **55.73** \\ \hline \hline \end{tabular}
\end{table}
Table 10: Statistical data of soil salinity prediction using OK of two modes by sub-district.  
Primary statistical data of soil salinity prediction using OCK of two measuring modes by sub-district are reported in Table 12.  
Figure 11: Spatial distribution of soil salinity prediction using OCK of two measuring modes: (**a**) HH and (**b**) VV.  
As shown in Figure 11, patterns of soil salinity distribution from the two modes at the sub-district level are slightly different. At the same time, in Table 12, the top three sub-districts of ECe of the HH mode, Non Thai, Ban Wang, and Khang Phlu, show the highest mean values of soil salinity, with a value from about 2557 to 6056 mS/m, while the top three sub-districts, namely, Banlang, Makha, and Sai O, display the lowest mean value of soil salinity, with a value from about 552 to 1127 mS/m. The top three sub-districts of ECe of the VV mode, Dan Chak, Ban Wang, and Khang Phu, show the highest mean soil salinity values, from about 2635 to 4973 mS/m. The top three sub-districts, Banlang, Makha, and Sai O, display the lowest mean value of soil salinity, from about 1044 to 1585 mS/m. Like IDW and OK, the CV value of the two modes displays the lowest at Thanon Pho, with a value of 13.68% and 6.88%, respectively, while the CV value of the two modes exhibits the highest at Non Thai, with a value of 89.07% and 63.39%, respectively.  
At the district level, the mean ECe value of topsoil (HH) is 2293.25 mS/m, with an SD of 1948.26 mS/m and a CV of 84.96%. Meanwhile, the mean ECe value of subsoil (VV) is 2401.32 mS/m, with an SD of 1338.48 mS/m and a CV of 55.74%. Like IDW and OK, the variation of soil salinity at the topsoil level is higher than at the subsoil level.  
Furthermore, the results of the accuracy assessment of the CCK method with the testing dataset are reported in Table 13. The ME and RMSE values of the HH mode are about 633.24 and 1240.76 mS/m, and those of the VV mode are about \(-144.97\) and 806.88 mS/m. The R\({}^{2}\) values of the HH and VV modes are 0.8538 and 0.8344, respectively. The PBIAS of HH is about \(-41.70\%\), and VV is about 5.82%.  
When comparing ME values between two measuring modes, VV has a lower mean error. Similarly, the RMSE value of VV is lower than HH. Likewise, the PBIAS value of VV has a lower magnitude. In the meantime, the R\({}^{2}\) values of HH and VV modes are slightly different, providing a very strong correlation between measured and predicted values.