# Independent System Calibration of Sentinel-1B
## 9 Interferometric Verification
### Repeat-Pass Interferometric Consistency Evaluation  
The analysis has been carried out by systematically seeking interferometric pairs with annotation files. A total of 419 interferometric pairs of acquisitions employing Sentinel-1A and Sentinel-1B and a total of 799 InSAR data pairs employing Sentinel-1B were analyzed. First, the mean Doppler centroid frequency for each image as a function of the acquisition date is shown in Figure 28. It can be seen that the mean Doppler frequency of Sentinel-1A is located around 0 Hz whereas Sentinel-1B has a Doppler centroid offset of larger than 100 Hz. However, at the end of the S-1B commissioning phase, this Doppler centroid offset was reduced to almost 0 Hz due to a S-1B attitude adjustment in pitch and yaw. Figure 29 presents a summary of the orbital InSAR baselines, the burst synchronization and the achieved common Doppler bandwidth for the combination of S1B-S1B (first column) and S1B-S1A (second column) pairs. In the first row measurements of the physical baseline (B), perpendicular baseline (\(B_{perp}\)), and parallel baseline (\(B_{par}\)) for all analyzed pairs are plotted, as a function of the geographic latitude. Table 7 summarizes the standard deviation of the geometrical baselines of all possible S1B-S1B and S1B-S1A pairs. Aside from the physical baseline in the zero Doppler plane, the perpendicular and parallel components are provided. In Table 8, the radial and across-track components of the baseline are shown, which have been derived from the parallel and perpendicular baselines. The Root Mean Square (RMS) perpendicular baseline when using only Sentinel-1B acquisitions is approximately 81 m and when combining Sentinel-1A with Sentinel-1B 89 m. The radial and across-track orbit components employing the S1B unit are 8.83 m and 66.16 m respectively, referred to one pass. These values are in agreement with previous analyses performed with Sentinel-1A [21] and the expected orbital tube size of about 100 m. \begin{table}
\begin{tabular}{l c c c} \hline \hline  & **Physical Baseline (B)** & **Perp. Baseline (\(B_{perp}\))** & **Parallel Baseline (\(B_{par}\))** \\ \hline S1B–S1B. Standard deviation & 94.4 m & 81.22 m & 63.67 m \\ S1B–S1A. Standard deviation & 105.82 m & 89.43 m & 73.35 m \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Standard deviation of the geometrical baselines for the S1B–S1B and S1B–S1A pairs. Figure 28: Mean Doppler centroid frequencies of Sentinel-1A and 1B units during the Sentinel-1B commissioning phase. The second row of Figure 29 shows the retrieved burst mis-synchronization (in milliseconds and meter units) as a function of the latitude. Apart from a few outliers, the burst synchronization is better than 5 ms (marked in the plots with red lines). If the outliers are removed, the standard deviation of the (InSAR) burst mis-synchronization is 3.7 ms for S1B-S1B pairs. The error of the mis-synchronization can be assumed to be the same for the master and slave acquisition, when employing only acquisitions of the S1B unit. This yields a (single acquisition) mis-synchronization of 2.6 ms. The standard deviation of the S1B-S1A burst mis-synchronization is 4.66 ms. Hence, the lower value of the S1B-S1B mis-synchronization indicates that the mis-synchronization is slightly worse when performing cross-interferometry. The percentage of the final common Doppler bandwidth, taking into account the burst mis-synchronization and the mean Doppler centroid frequencies, is plotted in the third row of Figure 29. It can be appreciated that in the case of employing only the S1B unit, some pairs present a common bandwidth smaller than 90%. In the case of combining S1B with S1A, the majority of pairs present a common bandwidth around or below 90%. This is due to the uncompensated S-1B SAR  
Figure 29: InSAR baselines, burst mis-synchronization and final common Doppler bandwidth for the combination of S1B–S1B (**first column**) and S1B–S1A (**second column**) InSAR data pairs.