## 3 Results and Discussion
### Important Features
\begin{table}
\begin{tabular}{l l l l l l l l l} \hline \hline [PERSON] et al. [162] & Spain, Field & 1D-CNN & Spectrophotometer & Spectral measurement from different soil samples & Over drying & SSM & - \\ \hline [PERSON] et al. [163] & Czech Republic, Field & XGBoost & Sentinel-2 & NDVI, NDRI, NDWL, DVI, RVI, MSI, elevation & EC-5 Sensor & 5-10 & - \\ \hline \multirow{3}{*}{[PERSON] et al. [164]} & Czech Republic, Field & \multirow{3}{*}{RF} & \multirow{3}{*}{UAV} & RGI, VVI, VDVL, VARI, TGI, SL, SHP, SCAL, NCRDL, NDTI, & \multirow{3}{*}{Oven drying} & \multirow{3}{*}{SSM} & \multirow{3}{*}{-} \\  & & & NDI, HI, GRVI, GL, GLAL, ESG, ERCBVE, CI, BI, RI, HEU, & & & & \\  & & & NDI, Slope, ProfCur, Plnc,VHE, VHE, TRI (1, 4), VFM (1, 4), & & & & \\  & & & TTI, IVW1, Temperature, GWL, SM. & & & & \\ \hline \multirow{3}{*}{[PERSON] et al. [80]} & New Zealand, Regional & RF & Sentinel-1 & Backscatter, incident angle, NDVI, slope, aspect, roughness & Capacitance- & \multirow{3}{*}{10} & \multirow{3}{*}{-} \\  & Regional & RF & Sentinel-1 & index, wetness index & AquaCheck & AquaCheck & \multirow{3}{*}{10} & \multirow{3}{*}{-} \\  & Regional & SVR & Landsat & & sub-surface & & & \\  & & & & probes & & & \\ \hline \multirow{3}{*}{[PERSON] et al. [165]} & Germany, Regional & \multirow{3}{*}{Germany, Field} & \multirow{3}{*}{LS-SVM, Cubist} & Sentinel-1, Landsat & VV, VH *, incident angle, NDVI *, height *, slope, and aspect & FDR & SSM & - \\ \cline{1-1} \cline{5-7}  & [PERSON] et al. [166] & Germany, Field & LS-SVM, Cubist & Spectrophotometer & VIS-NIR reflection & & & \\ \cline{1-1} \cline{5-7}  & & Fuzzy-means & \multirow{3}{*}{VIS-NIR} & \multirow{3}{*}{20} & \multirow{3}{*}{LS-SVM} & \multirow{3}{*}{20} & \multirow{3}{*}{LS-SVM} \\  & & sampling and & & sampling and & & & & \\ \cline{1-1} \cline{5-7}  & Regional & estimation & LIDAR & Elevation & & & \\ \cline{1-1} \cline{5-7}  & & approach & (PCM SSA) & & & & \\ \hline \multirow{3}{*}{[PERSON] et al. [168]} & \multirow{3}{*}{Germany, Field} & Fuzzy-means & \multirow{3}{*}{RapidFye sensor} & Fuzzy-means & \multirow{3}{*}{rNDVI, elevation, LAI} & TDR & \multirow{3}{*}{10} & \multirow{3}{*}{-} \\  & & sampling and & sampling and & & & & & \\ \cline{1-1} \cline{5-7}  & & estimation & RapidFye sensor & & & & & \\ \cline{1-1} \cline{5-7}  & & approach & & & & & & \\ \cline{1-1} \cline{5-7}  & & (PCM SSA) & & & & & & \\ \hline \multirow{3}{*}{[PERSON] et al. [169]} & Turkey, Regional & \multirow{3}{*}{GRNN} & \multirow{3}{*}{RADARSAT-2} & VV, VH, HV, HI, entropy, anisotropy, alpha angle, & Gravimetric & \multirow{3}{*}{3-5} & \multirow{3}{*}{-} \\  & volume scattering, odd bounce, double bounce & & method & & & & method \\ \hline \multirow{3}{*}{Sektertekin, Marangoz [170]} & Turkey, Regional & MLR & Sentinel-1 & VV, VH, incident angle & & & & \\ \cline{1-1} \cline{5-7}  & & & & & & & \\ \cline{1-1} \cline{5-7}  & & & & & & & \\ \hline \multirow{3}{*}{Usa [98]} & Turkey, Regional & \multirow{3}{*}{ANN} & Landsat 8 & EVI, SAVA, NDMI, NDWL, MSMI, THS 1, THS2, slope *, & & & & \\ \cline{1-1} \cline{5-7}  & & & TWI *, ALT, TI *, TRASP, EAST *, NORTH, SITE, CTI & & & & \\ \cline{1-1} \cline{5-7}  & & & Deep belief & Landsat, MODIS, & & & & \\ \cline{1-1} \cline{5-7}  & network & SMAP, ERA-5 & & LST, NDVI, albedo, precipitation, SMAP, ERA-5 SM & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._