Long-term stability of geoidal geopotential from Topex/Poseidon satellite altimetry 1993-1999

The TOPEX/POSEIDON (T/P) satellite altimeter data from January 1, 1993 to October 24, 1999 (cycles 11-261) was used for investigating the long-term variations in the geoidal geopotential W-0 and/or in the geopotential scale factor R-0 = GM/W-0 (GM is the adopted geocentric gravitational constant). The mean values determined for the whole period covered are: W-0 = (62 636 856.161 +/- 0.002) m(2) s(-2), R-0 = (6 363 672.5448 +/- 0.0002) m. The actual accuracy is limited by the altimeter calibration error (2-3 cm) and it is estimated to be about +/- 0.5 m(2) s(-2) (+/- 5 cm). The yearly variations of the above mean values are at the formal error level. No long-term trend in W-0, representing the ocean volume change, was found for the seven years period 1993-9 on the basis of T/P altimeter (AVISO) data. No sea surface topography model was used in the solution.