## 6 Conclusions
This given demonstration model is the beginning of estimating uncertainty with FRM standards and is to be improved after additional and accurate information is assimilated in the Cal/Val. Details on the way this table is constructed are given in an upcoming publication for the FRM4 ALT standardization [63], but it will not be detailed here as it is not the intent of this paper. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Standard Uncertainty** & **Uncertainty** & **Divisor** & **Standardized** & **Sensitivity** & **Uncertainty** & **Degrees of Freedom** \\  & **Estimates** & & **Uncertainty** & **Coefficient** & **Coefficient** & **Component** & **Degrees of Freedom** \\ \hline GPS Height Processing & 0.14 mm & 1 & 0.14 mm & 1 & 0.14 mm & 1759 \\ GPS Receiver Manufacturer & 6.0 mm & \(\sqrt{5}\) & 3.5 mm & 1 & 3.5 mm & 50 \\ GPS Antenna Reference Point, Lab Calibration & 2.0 mm & 1 & 2.0 mm & 1 & 2.0 mm & \(\infty\) \\ Water Level Observations & 1.3 mm & 1 & 1.3 mm & 1 & 1.3 mm & 19 \\ Tide Gauge Zero Offset & 5.0 mm & \(\sqrt{5}\) & 2.9 mm & 1 & 2.9 mm & 2 \\ Tide Gauge Vertical Masignment & 2.4 mm & \(\sqrt{5}\) & 1.4 mm & 1 & 1.4 mm & 50 \\ Tide Gauge Calibration Certificate & 5.5 mm & 1 & 5.5 mm & 1 & 5.5 mm & \(\infty\) \\ Split Levelling & 0.13 mm & 1 & 0.13 mm & 1 & 0.13 mm & 15 \\ GNSS and Tide Gauge Thermal Expansion & 1.1 mm & \(\sqrt{5}\) & 0.6 mm & 1 & 0.6 mm & 50 \\ Spirit Levelling Target Masignment & 1.0 mm & \(\sqrt{5}\) & 0.6 mm & 1 & 0.6 mm & 50 \\ Observer’s Experience & 1.0 mm & \(\sqrt{5}\) & 0.6 mm & 1 & 0.6 mm & 50 \\ Split Levelling Instrument & 1.0 mm & \(\sqrt{5}\) & 0.6 mm & 1 & 0.6 mm & \(\infty\) \\ Water Level at Tide Pole & 1.0 mm & \(\sqrt{5}\) & 0.6 mm & 1 & 0.6 mm & \(\infty\) \\ MSS/Geoid Models & 5.8 mm & 1 & 5.8 mm & 1 & 5.8 mm & 8 \\ Cal/Val Processing and Transformations & 0.5 mm & \(\sqrt{5}\) & 0.3 mm & 1 & 0.3 mm & 50 \\ Geoid Slope & 10.0 mm & \(\sqrt{5}\) & 5.8 mm & 1 & 5.8 mm & 50 \\ Unaccounted Uncertainty & 500 mm & \(\sqrt{5}\) & 28 mm & 1 & 28 mm & 50 \\ Root Sum Square & 52 mm & & 31.0 mm & 1 & 31 mm & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Uncertainty budget analysis for the sea-surface calibration methodology. All in all, the Gavdos and western Crete Cal/Val infrastructure includes at present 17 permanent Global Navigation Satellite System stations, 9 tide gauges, 7 meteorological systems, and one microwave transponder. Ocean tides in this part of the world are neither extreme nor vary drastically (a few cm), while the ocean circulation and the reference models have been well established for altimeter calibration over several decades. This Cal/Val facility is capable of calibrating ascending and descending orbits of the same altimeters, but also at crossover locations at sea in the open ocean around Crete. At the same location, connection and cross-comparison of various calibration processes can be made, using the same orbits, conditions, and settings, but also employing diverse methods and instrumentations (sea-surface and transponder). This work has presented calibration results based on the Cal/Val infrastructure in Gavdos and western Crete primarily for the reference missions of Jason-1, Jason-2, and Jason-3. It has also provided relative calibrations with respect to reference missions for other satellite altimeters, such as Sentinel-3A, HY-2A, and SARAL/AltiKa. At first, an attempt has been made to present the gradual and step by step development of the permanent ground infrastructure in Gavdos and western Crete for sea-surface and transponder altimeter calibration. This description covers a period from the early stages of this infrastructure development, more than about 15 years ago, till today (2018). This facility was originally built up in 2001 to calibrate the Jason satellite altimeters, but it eventually has contributed throughout its many years of operation into calibrating all international altimeters, such as those from the European Space Agency, as well as American, French, Chinese, and Indian satellites.