The geopotential value W 0 for specifying the relativistic atomic time scale and a global vertical reference system

Abstract

The TOPEX/Poseidon (T/P) satellite alti- meter mission marked a new era in determining the geopotential constant W0. On the basis of T/P data during 1993–2003 (cycles 11–414), long-term variations in W0 have been investigated. The rounded value W0 = 62636856.0 ± 0.5) m2s−2 has already been adopted by the International Astronomical Union for the definition of the constant LG = W0/c2 = 6.969290134 × 10−10 (where c is the speed of light), which is required for the realization of the relativistic atomic time scale. The constant LG, based on the above value of W0, is also included in the 2003 International Earth Rotation and Reference Frames Service conventions. It has also been suggested that W0 is used to specify a global vertical reference system (GVRS). W0 ensures the consistency with the International Terrestrial Reference System, i.e. after adopting W0, along with the geocentric gravitational constant (GM), the Earth’s rotational velocity (ω) and the second zonal geopotential coefficient (J2) as primary constants (parameters), then the ellipsoidal parameters (a,α) can be computed and adopted as derived parameters. The scale of the International Terrestrial Reference Frame 2000 (ITRF2000) has also been specified with the use of W0 to be consistent with the geocentric coordinate time. As an example of using W0 for a GVRS realization, the geopotential difference between the adopted W0 and the geopotential at the Rimouski tide-gauge point, specifying the North American Vertical Datum 1988 (NAVD88), has been estimated.