## 4 Sentinel-3A SRAL and MWR Cal/Val Results
### Sea-Surface Calibration Results  
The latest Sentinel-3A sea-surface height Cal/Val results are given in Figure 20 for the ascending Pass No.14 and the descending Pass No.335. It can be seen that the SSH bias along the ascending Pass No.14 is estimated to be \(-\)0.12 cm, while the descending Pass No.335 gave an SSH bias of \(-\)1.20 cm (\(N\approx 30\)). Both of these results carry a standard deviation for their internal dispersion of about \(\pm\)5 mm. These figures are to improve in confidence as soon as more calibrations are carried out. \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Contributing Error Constituent** & **Error Type** & **Variance Estimate** & **Standard Uncertainty** \\ \hline Measured range & B & 3.00 mm & \(\pm\)1.73 mm \\ Transponder Internal Delay & B & 30.00 mm & \(\pm\)15.00 mm \\ Dry tropospheric Delay & B & 2.00 mm & \(\pm\)1.16 mm \\ Wet tropospheric Delay & B & 14.00 mm & \(\pm\)8.10 mm \\ Ionospheric Delay & B & 4.00 mm & \(\pm\)2.31 mm \\ Geophysical corrections & B & 20.00 mm & \(\pm\)11.60 mm \\ Satellite orbit height & B & 50.00 mm & \(\pm\)29.00 mm \\ Pseudo-Doppler correction & B & 2.00 mm & \(\pm\)11.16 mm \\ GNSS instrument & B & 6.00 mm & \(\pm\)3.50 mm \\ GNSS antenna reference point & B & 4.00 mm & \(\pm\)2.00 mm \\ GNSS repeatability & A & 6.00 mm & \(\pm\)0.17 mm \\ GNSS-Transponder Leveling & A & 1.00 mm & \(\pm\)0.18 mm \\ Levelling instrument/method & B & 1.00 mm & \(\pm\)0.60 mm \\ Processing \& Approximations & B & 30.00 mm & \(\pm\)17.34 mm \\ Orbit Interpolations & B & 0.30 mm & \(\pm\)0.17 mm \\ Unaccounted effects & B & 20.00 mm & \(\pm\)11.60 mm \\
**Root-Sum Squared (Combined)** & & & \(\pm\)**41.50 mm** \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Uncertainty budget for the transponder calibration, following the International Standards Organization “Guide to the Expression of Uncertainty in Measurement” [38]. Uncertainty Budget for Sea-Surface Calibration  
By the same token, to estimate uncertainty of results in sea-surface calibration, the following main error components were identified [39]: (1) _Cal/Val site coordinate determination_. This group identified possible errors induced by the GNSS receiver, its antenna, ground stability, local setting, geodetic control ties, unaccounted effects, etc., and, by GNSS processing and data rectification strategies, to arrive at the absolute geodetic coordinates of the Cal/Val site. (2) _Sea-surface height at Cal/Val site_. The determination of the sea level at the Cal/Val site in an earth-centered earth-fixed reference system involved several error constituents related to water level observations (made by tide gauges), local conditions, models, for example for significant wave heights [41], setting and measuring and sampling strategies, instrument, monumentation and setting, ground deformation, earth tides, thermal expansion, atmospheric loading, local effects, reference time and coordinate frame for site positioning, etc., and to field leveling surveys when connecting water level records with absolute coordinates of reference site. (3) _Local Reference Surfaces_. The determination of sea level anomaly constituted the procedure with the largest uncertainty contribution in the sea-surface calibration. This was accomplished by dissecting the way models were applied for transferring heights from the Cal/Val site to open ocean using Mean Sea Surface, Mean Dynamic Topography, and geoid models, as well as the way their each individual uncertainty is combined to arrive at the final result for sea-surface calibration. (4) _Cal/Val processing and transformations_. The errors induced by the calibration processing and technique and the technique followed to transfer the coastal sea-surface height to the open sea were taken into consideration in this category. (5) _Unaccounted effects_. Additional effects which were not taken care of in the previous description.