# Potential of Sentinel-1 Radar Data for the Assessment of Soil and Cereal Cover Parameters
## 3 Results and Discussions
### Radar Signal Analysis
#### 3.2.3 Relationship between Radar Signal and Cereal Parameters  
In this section, the sensitivity of radar signals is discussed, for the case of two vegetation parameters: LAI and H. Figure 8 shows the relationship between the radar signals (VV and VH polarizations) and the LAI, for two moisture classes: mv \(\leq\) 15 vol. % and mv \(>\) 15 vol. %. Just two moisture classes were proposed, in order to include a sufficiently large number of observations. In the VV polarization, the radar sensitivity to LAI leads to a dynamic range of approximately 2 dB in both moisture classes, with the signal decreasing with increasing LAI. This behavior is due to the fact that when the LAI increases, it leads to stronger vegetation-induced attenuation of the backscattered soil signals. The behavior of the VH radar signals as a function of LAI is different to that observed in the VV polarization, and vegetation cover appears to have a relatively weak influence on the radar signal strength. In practice, when the vegetation-induced attenuation increases, this is accompanied by a decrease in the soil component of the total radar signal, and vegetation scattering (in particular, volume scattering, which is stronger in the VH polarization) increases with increasing LAI. [PERSON] et al. [52] have shown similar results for HH and VV-polarized radar observations (TSX data), in which the signal strength decreases as a function of increasing LAI. However, radar signals are not affected in the same way by all types of vegetation cover, since the radar signal is strongly dependent on the geometric structure characterizing each type of vegetation. As an example, [PERSON] et al. [44] observed a positive relationship between signal strength and LAI in the case of grass-covered fields. Figure 9 plots the VV and VH signals as a function of the second vegetation parameter, the vegetation height (H). This analysis was made for vegetation heights recorded until the beginning of April, corresponding to the end of the local period of plant growth. After this date, although the height of the plants remains constant, the vegetation is characterized by a decreasing level of vegetation water content. As in the case of the LAI observations, two moisture classes, mv \(\leq\) 15 vol. % and mv \(>\) 15 vol. %, were considered. In the VV polarization, very similar behaviors are observed, as in the case of the LAI parameterization. The VV radar signal strength can be seen to decrease with increasing vegetation height. In the low moisture class, there are no data points corresponding to vegetation higher than 100 cm, which could explain the observed decrease in correlation with respect  
Figure 7: S1 radar data as a function of the Hrms roughness parameter in two soil moisture (mv) classes: (**a**) VV polarization, mv \(\leq\) 10 vol. %; (**b**) VH polarization, mv \(<\) 10 vol. %; (**c**) VV polarization, 10 vol. % \(<\) mv \(<\) 20 vol. %; (**d**) VH polarization, 10 vol. % \(<\) mv \(<\) 20 vol. %. to the values determined for the high moisture class. As shown in Figure 9, in the VH polarization the radar signal strength increases with increasing vegetation height. This behavior appears to be contradictory to that observed in Figure 8, which reveals a weakly decreasing VH signal strength as a function of increasing LAI. This apparent discrepancy can be explained by the fact that ground-truth measurements began when the vegetation height was approximately 10-15 cm, following the first LAI campaigns. This means that the influence of the soil was lower, and that volume scattering from the vegetation (Figure 9) could have dominated the backscattered radar signals. Figure 8: S1 data as a function of LAI for two classes of soil moisture (mv): (**a**) VV polarization, mv \(\leq\) 15 vol. %; (**b**) VH polarization, mv \(\leq\) 15 vol. %; (**c**) VV polarization, mv \(>\) 15 vol. %; (**d**) VH polarization, mv \(>\) 15 vol. %. Figure 9: Sentinel-1 (S1) radar data as a function of H in two soil moisture (mv) classes: (**a**) VV polarization, mv \(<\) 15 vol.