## 4 Validation Results
### Along-Track Results  
The first and second tracks over the WG area were acquired on 2019-02-05 and 2019-09-15, respectively. The second track was during the monsoon season. Thus, a higher VWC is expected. At the time of the first track, the in situ soil moisture was 0.18 m\({}^{3}\) m\({}^{-3}\). For the second track, the in situ soil moisture was 0.51 m\({}^{3}\) m\({}^{-3}\), which is the saturation level. In the model, the soil clay percentage was set to 20%, and the DEM window size was set to nine samples for both tracks. Furthermore, the parameter \(\sigma_{L}\) of Equation (19) was set to 0.4\({}^{\circ}\) for both tracks. Selection of the previous two parameters was made empirically and acknowledging the fact that this area has rough topography. Moreover, the small-scale roughness \(\sigma_{S}\) was set to 1.25 cm, which is higher than the in situ measurements, but within the IGOT model validity. We expect the surface roughness to be higher than the in situ measurements, as the measurements were taken in a low relief area of the sites. Finally, the vegetation optical depth of the first track was zero, as we expected the vegetation to be dry. On the other hand, the vegetation parameter \(\kappa d\) of the second track was set to 0.2. This value was selected empirically to match CYGNSS reflectivity. All of the model parameters and the track information are summarized in Table 2.  
The WG track 1 SP and the in situ sensor locations are shown in Figure 6a. The peak reflectivity of both CYGNSS and IGOT is shown in Figure 6b. In the figure, the points between the two vertical orange lines are between the SoilSCAPE sites. As illustrated in the figure, the IGOT model reflectivity follows the CYGNSS reflectivity for most of the points on the track. Furthermore, the median difference between CYGNSS reflectivity and IGOT reflectivity is about 2.5 dB. An anticorrelation relation between the elevation and peak reflectivity of both the IGOT model and CYGNSS can be observed in Figure 6b. This is mainly due to the fact that the valley basins are smoother than the hills in this region, which results in higher reflectivity in the valleys. The WG track 2 SP and the in situ sensor locations are shown in Figure 7a. The peak reflectivity is shown in Figure 7b. As illustrated in the figure, the peak reflectivity of the IGOT-VEG model matches the CYGNSS reflectivity with good accuracy except for three DDMs. These DDMs lie between \(-110.25^{\circ}\) and \(-110.4^{\circ}\) longitudes, as shown in Figure 7a. For all peak reflectivity points on the track, the median value of the difference between CYGNSS and IGOT-VEG reflectivity is about 1.8 dB. The three outlier DDMs, which IGOT-VEG underestimated, are over the San Pedro river. This river could be the reason for the high CYGNSS reflectivity, as the high water level of the river during the monsoon season can cause strong coherent reflections and increase the DDM reflectivity, which is not accounted for in the parameterization of the IGOT model. The two tracks over JER were acquired within four hours of each other on 30 May 2022. Selection of the track length was made such that the DDM signal-to-noise ratio (SNR) is equal to or over 2 dB. All the DDMs in these tracks have an SNR between 2 dB and 10 dB. During these tracks, the in situ soil moisture was about 0.01 m\({}^{3}\) m\({}^{-3}\), which is very dry. Figure 6: WG track 1 : (**a**) Track elevation map; (**b**) Peak reflectivity. The SoilSCAPE sites are between the orange vertical lines. In the model, the soil clay percentage was set to 20%, and \(\sigma_{L}\) was set to be 0.1\({}^{\circ}\). The latter is lower than the value used for the WG tracks as this area is expected to have less topography, as illustrated in the elevation maps of Figures 8a and 9a. The small-scale roughness \(\sigma_{S}\) was set to 1.25 cm, which is close to the highest in situ roughness measurement. In the model, the DEM window size was set to 15 samples, which is larger than the value used for the WG tracks.