## 3 Materials and Method
### Methodology  
To achieve the goal of cost-effective groundwater exploration and recognize the influence of the likely parameters on the ACC, the unique features related to groundwater potential were configured and described by integrating RS and GIS techniques with favorable groundwater parameters in the same spatial resolution of 30 m \(\times\) 30 m, including lineaments and SMI derived from Landsat imagery, and SD, DD, and TWI analyzed from DEM. HGU was considered as the parameter of lithology to simultaneously reflect the complex spatial distribution of geological structures and rock types in the ACC. Therefore, six specific parameters, namely, HGU, LD, SD, DD, TWI, and a variation of the SMI (VSMI) were selected to compute the NGPI in the ArcGIS Spatial Analyst module using Equation (1). The values of ranking and weight may change in each case study. To avoid the subjective effect on each parameter, its equal weight and appropriate 5 classifications of ranking were used in this study. That is, the weighting of each parameter was designed to be the same value of 1. In addition, the ranking of each parameter was based on the low to high groundwater potential and computed by the scale value of 0-5. Except for the parameter of HGU, the data formats of the other 5 parameters were digital numbers to determine the best arrangement of values by Jenks Natural Breaks (JNB) classification method [60; 61] into 5 designed rankings. Therefore, it is helpful to understand the groundwater potential of each selected parameter in the RS-GIS model. Finally, the NGPI with 6 proposed parameters in each pixelwas computed with the values of 0-30 and normalized from 0 to 1 in the final synthesized map of groundwater potential. The results were evaluated according to in-situ well yield data from 72 wells. \[\text{NGPI}=\frac{\sum_{\text{i=1}}^{\text{i=6}}\text{P}_{\text{i}}\text{X}\text{ W}_{\text{i}}}{\sum_{\text{i=1}}^{\text{i=6}}\text{P}_{\text{i}\text{ max}}\text{X}\text{W}_{\text{i}}} \tag{1}\]  
where \(\text{P}_{\text{i}}\) is the ranking of each parameter given by the scale value of 0-5, and \(\text{W}_{\text{i}}\) is the weight of each parameter given by the same value of 1 in this study. As illustrated in the study framework in Figure 4, the selected parameters and products include: (1) generating a geological map with a scale of 1:25,000 established by the CGS and delineating HGUs to complete the post-produced hydrogeological map; (2) deriving LD and multiple temporal SMI from Landsat imagery; and (3) analyzing DEM to calculate SD, DD, and TWI. The processing of the parameters (Table 2 and Figure 5) and in-situ well yield data are introduced in Appendix A.  
Figure 4: Framework of the proposed mapping of groundwater potential. Figure 5: The six thematic maps of (**a**) hydrogeological units (HGUs), (**b**) lineament density (LD), (**c**) slope degree (SD), (**d**) drainage density (DD), (**e**) topographic wetness index (TWI), and (**f**) variation of the soil moisture index (V SMI), were computed by the normalized groundwater potential index (NGPI) as the raster-based empirical GIS model in the ArcGIS Spatial Analyst module with a spatial resolution of 30 m \(\times\) 30 m. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Parameters 1**} & \multicolumn{3}{c}{**Benefit to Groundwater Prospect**} \\ \hline \multicolumn{2}{c}{**(a) HGUs**} & \multicolumn{2}{c}{Geological section} & \multicolumn{2}{c}{Main rock type} & \multicolumn{1}{c}{Ranking (i + ii)} \\ \cline{3-5} \multicolumn{2}{c}{} & \multicolumn{1}{c}{(i)} & \multicolumn{1}{c}{(ii)} & \multicolumn{1}{c}{Ranking (i + ii)} \\ \hline \multirow{2}{*}{1} & \multirow{2}{*}{UCRK} & CP and LV section as well as those with unconsolidated rock, such as alluvium and river terrace. & \multirow{2}{*}{5} \\ \hline
2 & WFGR & & Gravel (2) & 3 \\ \hline
3 & WFSM & \multirow{2}{*}{WF (1)} & Mud (1) & 1 \\ \cline{3-5} \cline{4-5}
4 & WFSS & & Sandstone and shale (2) & 3 \\ \hline
5 & WFSH & & Shale (0) & 1 \\ \hline \hline \end{tabular}
\end{table}