# Sensitivity Analysis of Multi-Temporal Sentinel-1 SAR Parameters to Crop Height and Canopy Coverage
## 3 Results
### SAR Parameters and Their Correlation with Crop Height  
Almost in all visited fields, the mean backscatter values indicated similar tendency in four stages of crop growth. In Figure 8, mean backscatter coefficient (\(\sigma_{\rm VV}\) and \(\sigma_{\rm VH}\) and VV \(+\) VH) values of each sample site are determined and the correlation between the field measurements are presented. It is observed that the maize had high sensitivity at the beginning but starts to decrease when the maize height is higher than 150 cm at inflorescence emergence and heading stages. Sunflower is not sensitive to the crop height only when the sunflower height is greater than 90 cm. At the end of flowering and the inflorescence, it shows low sensitivity compared to its early and later stages. In comparison with maize and sunflower, wheat had relatively good sensitivity at the end of heading. Regarding wheat  
Figure 7: Flowchart of Sentinel-1 dual polarization SAR data processing. full infloresence which is varying in different heights, the correlation between SAR backscattering (VV VH and \(\sigma^{0}_{\text{VV}}\)) and wheat height is considerably less as in inferred from Figure 8c,f in growing stage. Table 3 gives the coefficient of determination (R\({}^{2}\)) between Sentinel-1 dual polarimetric SAR parameters and measured crop height for maize, sunflower and wheat. Both \(\sigma^{0}_{\text{VV}}\) and \(\sigma^{0}_{\text{VH}}\) showed high correlation (R\({}^{2}\) = 0.81 and 0.80 respectively) and VV + VH had highest correlation (R\({}^{2}\) = 0.82) with maize height at the early stage. Whereas the correlation between SAR parameters to sunflower height is very low (R\({}^{2}\) = 0.31) at the same stage. Almost all SAR parameters show relatively good correlation at the early stage of wheat. For instance, a good negative correlation with VH/VV intensity ratio and \(\sigma^{0}_{\text{VH}}\) are obtained at the early stage of wheat (R\({}^{2}\) = 0.66, and 0.65 respectively). However, all of the crops have very weak correlation or even they are not correlated and sensitive to plant height in the later stage. Amongst the H-Alpha decomposition parameters, Alpha (\(\alpha\)) decomposition parameter represents the highest correlation (R\({}^{2}\) = 0.67) with wheat height during the early growth stage. The maize height is relatively correlated with H-Alpha decomposition parameters at the early stage, although no considerable correlation is observed during the early stage of sunflower and at the later stage of wheat. Figure 9 shows the correlation between the H-Alpha decomposition parameters and crops height of maize, sunflower and wheat. Figure 8: Correlation between (**a**–**c**) intensity arithmetic calculation of VV + VH, (**d**–**f**) \(\sigma^{0}_{\text{VV}}\) backscatter, and (**g**–**i**) \(\sigma^{0}_{\text{VH}}\) backscatter values of maize, sunflower and wheat with their height during growing stages. Figure 9: Correlation between Entropy (**a**–c), Anisotropy (**d**–**f**) and Alpha (**g**–**i**) decompositions of maize, sunflower and wheat with their height during growing stages.