The location of the GAVDOS facility is under a crossing point of the original ground-tracksofTOPEX/PoseidonandthepresentonesforJason-1,andadjacenttoanENVISAT pass, about 50 km south of Crete, Greece. Ground observations and altimetry compar-isons over cycles 70 to 90, indicate that a preliminary estimate of the absolute measure-ment bias for the Jason-1 altimeter is 144.7 ± 15 mm. Comparison of Jason microwave radiometer data from cycles 37 and 62, with locally collected water vapor radiometer and solar spectrometer observations indicate a 1–2 mm agreement.