## 6 Conclusions  
The produced results on absolute calibration are concisely presented in Table 5 for Jason-1, Jason-2, and Jason-3. Bias results for the altimeters are based on sea-surface and transponder calibrations at Gavdos and western Crete Cal/Val facilities. Jason-2 and Jason-3 have been calibrated along the descending orbit No. 18 by the microwave transponder at the CDN1 Cal/Val site on the mountains of Crete and immediately 10 s later, the same satellites continued calibration relative to the sea surface with diverse techniques, infrastructure, and instrumentation with the Gavdos Cal/Val facility. Furthermore, relative calibrations of Sentinal-3A, HY-2A, and SARAL/AltiKa altimeters with respect to the reference mission of Jason-2 are given in the same Table 5.  
In the sequel, the performance of Jason-2 and Jason-3 has been investigated and cross-examined during their tandem mission from 28 March 2016, till 23 September 2016. Results have been based also upon the same CDN1 and Gavdos ground Cal/Val instrumentation and setting when satellites were flying on the same orbit for six months in unison, separated 80 s apart. Transponder calibration has been carried out based on their descending pass No. 18 only. A few seconds later, this satellite pass No. 18 has been calibrated with the other Gavdos Cal/Val facility, as Jason-2 and Jason-3 were flown immediately down south over the sea. Hence, cross-comparisons could be made for the same orbit, but with two and diverse independent calibration techniques of the sea surface and transponder. A short summary statement regarding the altimeter bias for all these satellites is as follows (see also Table 5, and Figure 36):  
1. Jason-1 has produced a sea-surface height bias of +3.5 cm and +4.7 cm along the ascending and the descending orbits, respectively, around Gavdos. The mean value of this Jason-1 altimeter comes to +4.1 cm based on cycles 70 to 100 and the GRD-E data products. 2. Jason-2 exhibits an altimeter bias in determining sea-surface heights of +0.33 cm (ascending No. 109) and to a value of +0.63 cm for its descending orbit No. 18. Hence, the mean value for Jason-2 comes to almost zero (i.e., +0.48 cm). These results were based on the Gavdos Cal/Val, and Cycles 2-303 with GDR-D data products for Jason-2. 3. The transponder at CDN1 Cal/Val facility has produced a range bias for Jason-2 of \(-\)1.2 cm for Cycles 267-303 with SGDR-D and Level-2 data products. The associated SSH bias of Jason-2 along Pass No. 18 for the same cycles amounts to +1.7 cm based on Gavdos Cal/Val facility. Biases derived using transponder and sea surface techniques exhibited absolute values of about the same magnitude but with opposite signs. These results back each other up as they are determined by diverse calibration techniques, different locations, settings, and instrumentation;
4. Jason-3 demonstrated a bias at determining sea-surface heights of \(-\)0.50 cm along the ascending orbit and \(-\)0.74 cm along its descending orbit, as determined by the Gavdos Cal/Val site. Results were based on GDR-D products and its first 80 cycles of Jason-3. The mean value of the SSH bias of Jason-3 came to \(-\)0.62 cm when averaged over the ascending and its descending pass. 5. The transponder at the CDN1 Cal/Val site demonstrated a range bias of +0.76 cm for Jason-3, based on Cycles 5-80 with S-GDR products and precise orbits. 6. During the tandem mission, the offset in biases of Jason-3 with respect to Jason-2 for the SSH came to \(-\)2.66 cm, while it became +1.77 cm when ranges were directly evaluated with the transponder. The average bias offset of Jason-3 with respect to Jason-2 amounted to +2.21 cm (mean of transponder and SSH);
7. Sentinel-3A appeared to exhibit a relative offset in sea surface heights of +4 cm with respect to Jason-3 with crossover analysis. This value was also confirmed using a simultaneous transponder pass over the CDN1 Cal/Val site on 11 November 2016, where a range bias of \(-\)2.5 cm (i.e., opposite sign when compared to SSH bias) was determined. 8.