# Calibrating the SAR SSH of Sentinel-3A and CryoSat-2 over the Corsica Facilities
## 3 Results
### CryoSat-2 SSH Calibration
The CryoSat-2 SSH bias is then:  
- CryoSat-2 SAMOSA2: \(-\)746 \(\pm\) 5.5 mm (\(-\)73 \(\pm\) 5.5 mm for baseline C)  
- CryoSat-2 SAMOSA+: \(-\)746 \(\pm\) 5.0 mm (\(-\)73 \(\pm\) 5.0 mm for baseline C)  
We were unable to find in the literature another value of the CryoSat-2 absolute SSH bias (using sea level in situ measurements), but our results look very coherent with the updated Svalbard transponder result [20]: 722 \(\pm\) 6 mm (standard deviation of 29 mm, baseline B, before correcting the 673 mm known range bias). It is worth noting that the 24 mm remaining difference between these two determinations can be due to the geophysical corrections, and notably that the SSB is not affecting the transponder processing. For pass #4794, overflying both the Senetosa and Ajaccio facilities, we computed the averaged time series in the same way as for the Sentinel-3A pass shown in Figure 7. This is presented in Figure 10, where the average SSH bias from the Ajaccio and Senetosa overflights (5 s time lag and 37 km distance)  
Figure 8: Example of retracking improvement for pass #2426 cycle 001. The upper panels of (**a,b**) show the altimeter SSH (crosses) without geoid correction, while the lower ones show the altimeter SSH after geoid correction (stars with error bars). An automatic outlier detection is performed and the rejected data are circled. (**a**) Corresponds to the G-POD standard retracking (SAMOSA2) while (**b**) corresponds to the improved retracking (SAMOSA+ is the SAMOSA2 model tailored for inland water, sea ice and coastal zone domains). (**c**) Shows a zoom of the data locations (circles) very close to the coast; the white rectangle represents the SAR footprint for one data; the black lines correspond to the Catamaran-GPS tracks [4] that were used to map the Senetosa geoid (colored map in background). showed a very low standard deviation (15 mm for SAMOSA+ and 17 mm for SAMOSA2) and a bias very close to the global average: \(-\)740 mm for SAMOSA+ and \(-\)741 mm for SAMOSA2 vs. \(-\)746 mm for the global average (for both SAMOSA+ and SAMOSA2). For comparison, with a similar configuration, the standard deviation over 13 cycles for Sentinel-3A was 24 mm. Figure 10: Example of pass #4794 with a configuration \(\approx\) a la \(\approx\) Sentinel-3A from which the SSH biases from Ajaccio and Senetosa were averaged (using SAMOSA+). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Passes**} & \multicolumn{4}{c}{**SAMOSA2**} & \multicolumn{4}{c}{**SAMOSA+**} & \multirow{2}{*}{**Comment**} \\ \cline{2-2} \cline{4-7}  & **Mean (mm)** & \(\sigma\) **(mm)** & & & & & & \\ \hline Ajaccio & & & & & & & & \\
3563 & NA & NA & NA & NA & NA & NA & Coastal \({}^{*}\) \\
4077 & \(-\)746 & 32 & 5 & \(-\)743 & 30 & 5 & Coastal \({}^{*}\) \\
4794 & \(-\)727 & 36 & 5 & \(-\)731 & 24 & 5 & Coastal \({}^{*}\) \\
5308 & NA & NA & NA & NA & NA & NA & Coastal \({}^{*}\) \\ Average & \(-\)736 & 33 & 10 & \(-\)737 & 26 & 10 & \\ Senetosa & & & & & & & \\
0681 & \(-\)766 & 17 & 5 & \(-\)768 & 14 & 4 & d \textgreater{} 3 km \\
1195 & \(-\)733 & 23 & 3 & \(-\)733 & 23 & 3 & d \textgreater{} 8 km \\
2426 & \(-\)757 & 36 & 4 & \(-\)756 & 35 & 4 & Coastal \({}^{*}\) \\
4794 & \(-\)742 & 26 & 6 & \(-\)746 & 23 & 6 & d \textgreater{} 13 km \\ Average & \(-\)751 & 27 & 18 & \(-\)751 & 26 & 17 & \\ Total & \(-\)746 & 29 & 28 & \(-\)746 & 26 & 27 & \\ \hline \hline \multicolumn{7}{l}{\({}^{*}\) Coastal means that we take the measurements up to the coast; for the others the distance “d” is the closest measurement to the coast.} \\ \end{tabular}
\end{table} 
Table 3: Details of the SSH biases for each pass and for the two retrackers (SAMOSA2 and SAMOSA+). Figure 9: Time series of the CryoSat-2 SSH biases for each pass and the averages from Ajaccio, Senetosa and both (dash black line): (**a**) corresponds to the G-POD standard retracking (SAMOSA2) while (**b**) corresponds to the improved retracking (SAMOSA+) tuned for coastal, inland waters and ice.