# Relating Sentinel-1 Interferometric Coherence to Moving Events on Grasslands
## 3 Results and Discussion
### Dependence on Time Separation
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**RON** & **T\(-\)1** & **T\(+\)1** & **T\(+\)2** & **T\(+\)3** & **(T\(+\)1)\(-\)(T\(-\)1)** & **(T\(+\)2)\(-\)(T\(-\)1)** & **(T\(+\)3)\(-\)(T\(-\)1)** \\ \hline R160 & 0.16 (0.16) & 0.28 (0.30) & 0.23 (0.27) & 0.22 (0.22) & 0.12 (0.14) & 0.067 (0.11) & 0.064 (0.062) \\ R58 & 0.17 (0.17) & 0.25 (0.25) & 0.23 (0.23) & 0.20 (0.20) & 0.081 (0.086) & 0.061 (0.066) & 0.035 (0.035) \\ R80 & 0.16 (0.16) & 0.19 (0.21) & 0.20 (0.21) & 0.19 (0.19) & 0.034 (0.048) & 0.044 (0.051) & 0.033 (0.031) \\ \hline \end{tabular}
\end{table} 
Table 4: Median coherence values for time separation groups and VH polarisation. Values without parentheses indicate unfiltered data, while precipitation filtered data is given in parenthesis. Figure 8: Boxplots of coherence and time separation from a moving event. Grey boxplots represent unfiltered data, while white boxplots represent the precipitation filtered data. The T\(+\)1 group gave the best separation between the moved and not moved grasslands. In most cases, the upper quartile of the T\(-\)1 group and the lower quartile of the T\(+\)1 group did not overlap. The difference in median values for T\(-\)1 and T\(+\)1 groups was smallest for the R80 morning pass geometry. Even after the moving, coherence values stayed close to 0.20. This was most probably caused by dew, which can decrease the coherence, as it affects the dielectric constant that shapes the backscattering intensities of grass and also the reflection properties in the vegetation layer, thus influencing the phase. The lowest coherence could be expected when one of the images in the coherence pair was taken in dew conditions and the other in dry conditions. Even when both images were taken in the dew conditions, the spatial distribution of water drops in the vegetation layer was most probably random, leading to low coherence values. Variation of coherence was lower for T\(-\)3, T\(-\)2, and T\(-\)1 groups compared to T\(+\)1, T\(+\)2, and T\(+\)3 groups. Temporal decorrelation caused by tall grass decreases coherence values close to the noise floor. On the other hand, the decorrelation caused by the movement of plants was much smaller for shorter grass. In this case, other effects, such as weather conditions and human activities make the coherence much more variable. The medians of groups T\(-\)3 and T\(+\)3 are not significantly different. Taking into account R160 and R58 geometries, the average difference between precipitation filtered T\(-\)1\({}_{R160,R58}\) median compared to T\(+\)1\({}_{R160,R58}\), T\(+\)2\({}_{R160,R58}\), and T\(+\)3\({}_{R160,R58}\) groups is 0.084 for \(\gamma_{vh}\) and 0.064 for \(\gamma_{vv}\). Therefore, VH polarisation might have a slightly better ability to detect moving events. On average, the confidence interval for VH median at the 95% confidence level is 0.035, and for VV median it is 0.031. A similar outcome has been observed in studies focused on the use of SAR backscatter for agricultural monitoring. [PERSON] et al. [PERSON] et al. (2014) reported that the X-band HV polarisation is more sensitive to grasslands parameters than HH. Additionally, [PERSON] et al. [PERSON] et al. (2016) concluded that the co-pol channels (HH and VV) have a slightly lower potential for the detection of the sugarcane harvest. Taking into account all three image acquisition geometries, precipitation filtering affected the T\(+\)1, T\(+\)2, and T\(+\)3 groups more than the T\(-\)1, T\(-\)2, and T\(-\)3 groups. For T\(-\)1, T\(-\)2, and T\(-\)3, the average difference in medians between filtered and unfiltered data was under 0.10%. At the same time, the average difference for T\(+\)1, T\(+\)2, and T\(+\)3 groups was 4.9%. High vegetation decorrelates both in dry and wet conditions; thus, the removal of events with precipitation has little effect for T\(-\)1, T\(-\)2, and T\(-\)3 groups. The median values of precipitation filtered and unfiltered groups were not statistically significantly different.