# Relating Sentinel-1 Interferometric Coherence to Moving Events on Grasslands
## 3 Results and Discussion
### Dependence on Time Separation  
A decreasing trend in coherence values before a moving event and an increase after it could be observed. These trends are presented in Figure 7. In the case of rain, the coherence rarely exceeded 0.25. There were no clear gaps in the time separation values, indicating that there were enough samples to investigate the relationship between the coherence and time separation from a moving event. Figure 5: Scatterplot of coherence values and the sum of 3-h precipitation estimates at 300 m \(\times\) 300 m spatial resolution based on weather radar data for the first image pair available within 12 days after a moving event. R160 is represented by red, R80 by green, and R58 by blue dots. Figure 6: Box plots comparing coherence values for two groups—where the sum of 3-h precipitation estimates was >0.25 and \(\leq\)0.25 mm. Group sizes are given in parenthesis. Coherence values and the sum of precipitation estimates are calculated for first image pair within 12 days after a moving event. The box extends to first (Q1) and third (Q3) quartile values, the whiskers extend to 1.5 times interquartile range (IQR = Q3 \(-\) Q1) from the box (e.g., Q1 \(-\) 1.5 \(\times\) IQR), beyond the whiskers, data points are considered outliers. The notches around the median represent 95% confidence intervals calculated with 5000 bootstrap cycles. The coherence values were divided into six 12-day interval groups based on the time separation to investigate the changes in coherence (Table 3). Not all of the 12-day repeat-pass acquisitions for R80 and R58 were available, thus twelve time separation groups out of eighteen had coherence measurements for all 77 moving events. Precipitation filtering based on precipitation values >0.25 mm had the highest influence on the number of samples for R80, where 16% (R160 13%, R58 10%) of the samples were removed. Results show that T+1, T+2, and T+3 median \(\gamma_{vv}\) and \(\gamma_{vh}\) values were statistically significantly higher compared to group T-1 (Figure 8). The exact median values for the time separation groups and differences between them are given in Table 4 for VH and in Table 5 for VV. The moving event influenced median \(\gamma_{vv}\) and \(\gamma_{vh}\) values significantly, even after 24 to 36 days after the moving event. The only exception in the data set was the morning acquisition geometry R80 \(\gamma_{vv}\) T+3\({}_{R80}\) group, for \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Group** & **Range** & **R58** & **R80** & **R160** \\ \hline T\(-\)3 & \(-36\ldots-24\) & 77 (69) & 77 (61) & 77 (77) \\ T\(-\)2 & \(-24\ldots-12\) & 77 (77) & 77 (70) & 77 (67) \\ T\(-\)1 & \(-12\ldots 0\) & 63 (56) & 77 (71) & 77 (67) \\ T+1 & \(0\ldots+12\) & 55 (38) & 77 (53) & 77 (58) \\ T+2 & \(+12\ldots+24\) & 69 (59) & 68 (50) & 77 (57) \\ T+3 & \(+24\ldots+36\) & 77 (77) & 55 (55) & 77 (76) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Time groups used in the time separation analysis. The range defines days before the moving event (\(-\)) or after the event (\(+\)). The R58, R80, and R160 columns contain the number of samples for each group and their respective geometries. The number of samples after precipitation filtering is also given in parenthesis. Figure 7: Scatterplot of coherence values and time separation between the first image acquisition in coherence pair and a moving event. Blue dots mark the coherence values with 3-h precipitation estimates >0.25 mm. which the median was not significantly different from the T\(-1_{R80}\) group median. Increase of coherence after a moving event is in line with a similar previous study that was based on X-band data and 1-day interferometric pairs [27]. In contrast to that study, the use of C-band in this experiment might have ensured that the coherence values were statistically significantly higher for a period of up to 36 days after an event.