## 3 Results and Discussion
### Important Features
#### 3.4.2 Input Features for Field Scale vs. Regional/Global Scale
(2019)} & \multirow{2}{*}{China, Regional} & RF, GRN, XGboost, & \multirow{2}{*}{UNV} & \multirow{2}{*}{NDV, EV, CVN, TVDN, TODI} & \multirow{2}{*}{FDR-TRIME} & 0-10, 10-20, & \multirow{2}{*}{Caffeout} \\  & & LightGMM & & & & 40-50, 50-60 & \\ \hline \multirow{2}{*}{Marmenom} & \multirow{2}{*}{China, Regional} & RF, GRN, XGboost, & \multirow{2}{*}{UNV} & \multirow{2}{*}{NDV, EV, CVN, TVDN, TODI} & \multirow{2}{*}{FDR-TRIME} & 0-10, 10-20, & \multirow{2}{*}{Caffeout} \\  & & LightGMM & & & & 40-50, 50-60 & \\ \hline \multirow{2}{*}{Marmenom} & \multirow{2}{*}{China, Regional} & RF & GRN, XGboost, & \multirow{2}{*}{UNV, FIL, altitude, aspect, local sleep angle, incident angle, cost(0),} & \multirow{2}{*}{Neutron-probe} & 0-5 m & ANN \\  & & LightGMM & & & & 40-50, 450-60 & \\ \hline \multirow{2}{*}{Marmenom} & \multirow{2}{*}{Finland, Regional} & \multirow{2}{*}{GMM} & \multirow{2}{*}{Sentiland-1} & \multirow{2}{*}{Latin} & \multirow{2}{*}{time difference between the SM measurement and SAR image} & \multirow{2}{*}{WET-2 and PR2} & \multirow{2}{*}{S8M, 10, 20-30, } & \multirow{2}{*}{-} \\  & & LightGMM & & & & 40-50, 450-60 & \\ \hline \multirow{2}{*}{[PERSON] et al. (2020)} & Australia, & \multirow{2}{*}{LightGMM} & \multirow{2}{*}{MODS} & \multirow{2}{*}{T, R, RH, rainfall, latitude, longitude, MOOS bands, LST, set} & \multirow{2}{*}{-} & \multirow{2}{*}{1-6 m} & \multirow{2}{*}{-} \\  & & Regional & & & & 40-50, 450-60 & \\ \hline \multirow{2}{*}{[PERSON] et al. (2015)} & Australia, & RF, LR, MLF, SVM, & \multirow{2}{*}{Softage Regression} & Sentinel-1, & \multirow{2}{*}{Sentiland-1 and Sentinel-2 images} & \multirow{2}{*}{Embedded SM} & \multirow{2}{*}{10-120} & \multirow{2}{*}{RF} \\  & & Regional & & & & & \\ \hline \multirow{2}{*}{[PERSON] et al. (2016)} & Australia, & \multirow{2}{*}{Regional} & \multirow{2}{*}{MLP} & \multirow{2}{*}{SV, relative SSM, LST, NDVI, land cover, clay, SOC, AWC} & \multirow{2}{*}{TDR} & 0-30-30, 20 to 60 \\ \cline{1-1} \cline{3-3} \cline{5-6}  & & & & & \\ \hline \multirow{2}{*}{[PERSON] et al. (2018)} & Australia, & \multirow{2}{*}{Regional} & LSTM, & \multirow{2}{*}{SAME MOOS} & \multirow{2}{*}{S8M, soil moisture indices, weather variables} & \multirow{2}{*}{-} & \multirow{2}{*}{80} & \multirow{2}{*}{-} \\  & & Multi-head TNN, & \multirow{2}{*}{Hybrid DNN} & \multirow{2}{*}{Hybrid DNN} & \multirow{2}{*}{SAME MOOS} & \multirow{2}{*}{S8M, soil moisture indices, weather variables} & \multirow{2}{*}{-} & \multirow{2}{*}{80} & \multirow{2}{*}{-} \\ \cline{1-1} \cline{3-3} \cline{5-6}  & & & ANN & MOOS & & & 40-50, 50-60 & \\ \hline \multirow{2}{*}{[PERSON] et al. (2017)} & Global & ANN & \multirow{2}{*}{MODS} & \multirow{2}{*}{NOV + SSL, SWI + SSM} & \multirow{2}{*}{-} & \multirow{2}{*}{30, 55} & \multirow{2}{*}{-} \\  & & In the input feature column, asterisk (\(\uparrow\)) indicates the most important features for root zone soil moisture estimation. Off. Organic Matter, RD: Bulk Density, AWC: Available Water Capacity, Kai: Standard Hydraulics, Conductivity, SOC: Soil Organic Carbon, SMC: Soil Moisture Content, RC: Electrical Conductivity, MDV: Normalized Difference Vegetation Index, C1: Enhanced Vegetation Index, C2: Left Area Index, FG:, Actual Evaporation, PET: Potential Evaporation, R: Solar Radiation, HR: Relative humidity, T: Temperature, U: Wind Speed, VP: Vapor Pressure Debield, LST: and Surface Temperature, TW: Epoggio: Wireless Index, T: Temperature, SW: Surface Soil Moisture. All the abbreviations can be found in the Supplementary Table S3.