## Abbreviations  
The following abbreviations are used in this manuscript: \begin{tabular}{l l} ANN & Artificial Neural Network \\ API & Application Programming Interface \\ DL & Deep Learning \\ ESA & European Space Agency \\ GEE & Google Earth Engine \\ ISMN & International Soil Moisture Network \\ LSTM & Long Short Term Memory \\ MAE & Mean Absolute Error \\ MSE & Mean Square Error \\ NDVI & Normalized Difference Vegetation Index \\ RMSE & Root Mean Square Error \\ RNN & Recurrent Neural Network \\ SAR & Synthetic Aperture Radar \\ S1 & Sentinel-1 \\ S2 & Sentinel-2 \\ SM & Soil Moisture \\ SGD & Stochastic Gradient Descent \\ SMAP & Soil Moisture Active Passive \\ SMOS & Soil Moisture and Ocean Salinity \\ \end{tabular} \begin{table}
\begin{tabular}{l l l l l l l l l l l l l l} \hline
**Station ID** & **Network** & **Station Name** & **Clay** & **Sand** & **Silt** & \(NDV1\_min\) & \(NDV1\_max\) & \(NDV1\_mean\) & **CC-1** & **CC-II** & **CCC** & **MAE** \\ \hline
139 & FR\_Aqui & hillan2 & 13 & 69 & 18 & 0.377 & 0.823 & 0.661 & C & Cf & Tree & 0.022 \\
140 & FR\_Aqui & Vermetree & 19 & 48 & 33 & 0.247 & 0.994 & 0.593 & C & Cf & Cropland & 0.022 \\
292 & HOAL & Hoal\_02 & 23 & 30 & 47 & 0.361 & 0.872 & 0.592 & C & Cf & Cropland & 0.051 \\
617 & REMEDHUS & Cas\_Periles & 21 & 48 & 31 & 0.112 & 0.934 & 0.321 & C & Cs & Cropland & 0.020 \\
619 & REMEDHUS & El\_Coto & 18 & 51 & 32 & 0.125 & 0.581 & 0.267 & C & Cs & Cropland & 0.028 \\
620 & REMEDHUS & El\_Tomillar & 16 & 54 & 30 & 0.150 & 0.471 & 0.234 & C & Cs & Cropland & 0.019 \\
622 & REMEDHUS & Guarria & 16 & 51 & 34 & 0.130 & 0.612 & 0.366 & C & Cs & Cropland & 0.067 \\
624 & REMEDHUS & La\_Cruz\_de\_Elias & 21 & 48 & 31 & 0.097 & 0.381 & 0.226 & C & Cs & Cropland & 0.046 \\
625 & REMEDHUS & Las\_Arenas & 16 & 55 & 29 & 0.093 & 0.303 & 0.214 & C & Cs & Cropland & 0.042 \\
626 & REMEDHUS & Las\_Bodegas & 21 & 46 & 33 & 0.233 & 0.565 & 0.406 & C & Cs & Cropland & 0.033 \\
627 & REMEDHUS & Las\_Brozas & 17 & 52 & 31 & 0.195 & 0.303 & 0.228 & C & Cs & Cropland & 0.025 \\
628 & REMEDHUS & Las\_Eritas & 23 & 49 & 28 & 0.110 & 0.431 & 0.260 & C & Cs & Cropland & 0.028 \\
629 & REMEDHUS & Las\_Tres\_Rays & 20 & 49 & 32 & 0.155 & 0.470 & 0.310 & C & Cs & Cropland & 0.037 \\
630 & REMEDHUS & Las\_Vacas & 21 & 52 & 27 & 0.083 & 0.486 & 0.222 & B & S & Cropland & 0.031 \\
631 & REMEDHUS & Las\_Victorias & 20 & 49 & 31 & 0.113 & 0.479 & 0.217 & C & Cs & Cropland & 0.022 \\
633 & REMEDHUS & Pareedinas & 17 & 53 & 30 & 0.154 & 0.514 & 0.281 & C & Cs & Cropland & 0.018 \\
634 & REMEDHUS & Zamarron & 20 & 48 & 32 & 0.037 & 0.252 & 0.177 & C & Cs & Cropland & 0.027 \\
639 & RSMN & Bades & 28 & 27 & 44 & 0.287 & 0.752 & 0.562 & C & Cf & Urban & 0.026 \\
659 & SCAN & AAMU\_lig & 18 & 25 & 57 & 0.266 & 0.863 & 0.773 & C & Cf & Grassland & 0.041 \\
661 & SCAN & Adams\_Ranch\_\#1 & 17 & 59 & 24 & 0.177 & 0.417 & 0.294 & B & Bs & Shrubland & 0.026 \\
665 & SCAN & Clarkish & 18 & 52 & 30 & 0.300 & 0.648 & 0.412 & C & Cs & Tree & 0.018 \\
689 & SCAN & Codora\_Ranch & 15 & 57 & 28 & 0.091 & 0.177 & 0.114 & B & Bs & Shrubland & 0.012 \\
698 & SCAN & Deep\_Springs & 10 & 69 & 21 & 0.049 & 0.166 & 0.113 & B & Bw & Shrubland & 0.020 \\
713 & SCAN & Fort\_Reno\_f1 & 18 & 35 & 46 & 0.022 & 0.727 & 0.445 & C & Cf & Grassland & 0.038 \\
715 & SCAN & French\_Gulch & 19 & 47 & 34 & 0.336 & 0.671 & 0.436 & C & Cs & Tree & 0.046 \\
719 & SCAN & Goodwin\_Creek\_Tmber & 12 & 17 & 71 & 0.575 & 0.894 & 0.769 & C & Cf & Grassland & 0.027 \\
729 & SCAN & Holden & 20 & 40 & 40 & 0.083 & 0.233 & 0.124 & B & Bs & Shrubland & 0.020 \\
746 & SCAN & Knox\_City & 18 & 42 & 41 & 0.166 & 0.508 & 0.304 & C & Cf & Cropland & 0.038 \\
747 & SCAN & Koptis\_Farms & 16 & 58 & 25 & 0.171 & 0.765 & 0.587 & C & Cf & Cropland & 0.029 \\ \hline \end{tabular}
\end{table} 
Table 11: Soft texture, NDVI, climate and land-cover class features of stations with their MAE of SM prediction.