## 4 Results and Discussion  
### Characterization of SM and LST over the Study Area  
Figure 3 shows the diurnal and the annual cycles of in situ SM (blue line) and LST (red line) observations from the REMEDHUS network during the study period (2011-2014), averaged over all stations. The error bar indicates the standard deviation (std) among the 21 stations. In the diurnal cycle (left), the hourly mean LST exhibits a considerable diurnal range (from \(\sim\)13 \({}^{\circ}\)C to \(\sim\)19 \({}^{\circ}\)C), and the daily minimum and maximum LST (\(T_{min}\) and \(T_{max}\)) occur at 7 h and at 16 h, respectively. These times approximately correspond to the SMOS morning and afternoon passes over the REMEDHUS region. Additionally, the LST variability among the stations is higher when the LST is high (std LST \(\sim\)2 \({}^{\circ}\)C) than when the LST is low (std LST \(\sim\) 1 \({}^{\circ}\)C). By contrast, the hourly mean SM remains almost constant (\(\sim\)0.13 m\({}^{3}\)/m\({}^{3}\)); its variation along the day is within the accuracy of the sensor, and the SM variability among the stations is low (std SM \(\sim\) 0.09 m\({}^{3}\)/m\({}^{3}\)). The stability of the daily SM indicates that a unique SM value per day could be representative of the entire day, except when rainfall events occur. In this line, previous research studied the temporal evolution of SM in this region and verified its persistence for a few hours per day, and even during a few days [54]. Also, in a SMOS L2 SM validation study at the same area, no differences where detected between using the time-overpass or the daily average of the in situ SM values [40]. In the annual cycle (right), the monthly mean of SM and LST present opposite behaviors, with the lowest SM and the highest LST during summer months (June, July and August), and the highest SM and the lowest LST during winter months (December, January and February). The SM annual cycle ranges from \(\sim\)0.07 m\({}^{3}\)/m\({}^{3}\) to \(\sim\)0.2 m\({}^{3}\)/m\({}^{3}\) and the LST annual cycle ranges from \(\sim\)6 \({}^{\circ}\)C to \(\sim\)27.7 \({}^{\circ}\)C. The variability in SM is higher in winter (std SM \(\sim\) 0.12 m\({}^{3}\)/m\({}^{3}\)) and lower in summer (std SM \(\sim\) 0.05 m\({}^{3}\)/m\({}^{3}\)), whereas variability in LST is lower in winter (std LST \(\sim\) 0.8 \({}^{\circ}\)C) and higher in summer (std LST \(\sim\) 2 \({}^{\circ}\)C). These values are consistent with the temporal evolution of SM from the ground-based measurements from the last 15 years of data recorded in REMEDHUS [55] and the climate type of this region.  
The possible relation of SM and LST dynamic ranges with soil texture is explored in Figure 4. For the case of SM (left), a very strong anticorrelation with the soil sand content (red asterisks, R = \(-\)0.93) and a strong correlation with the soil clay content (blue crosses, R = 0.86) is observed. Two stations (H9 and M13) present a higher SM dynamic range compared with the other stations. This can be explained by the fact that they are forest-pasture stations. Also, they are located at the bottom of valleys where the water table is shallow in winter, and where occasional flooding occurs [40]. In the case of LST (right), a non-significant correlation of LST dynamic range with the soil sand or clay content is found.  
Figure 3: Diurnal (**left**) and annual (**right**) cycles of in situ SM (blue line) and LST (red line) from the REMEDHUS network during the study period. The error bar indicates the standard deviation (std) among the 21 stations.