Report of Special Commission 3 of IAG
Abstract
Since the last presentation of Special Commission 3 on numerical values of fundamental geodetic parameters at the International Astronomical Union (IAU) General Assembly at Kyoto in 1997, there were some conceptual as well as fundamental numerical changes. The four basic parameters of geodetic (ellipsoidal) reference systems (GRS) can no longer be considered as constant with time: J(sub 2), alpha, omega, and GM have to be replaced by clearly (+/- 10(exp -8) or better) specified mean values, they have to be associated with a specific epoch, or, in case of GM, with specific reference frames (alpha = semi-major axis of Earth ellipsoid, J(sub 2) = second degree zonal harmonic of geopotential, omega = spin of Earth rotation). In case of (alpha, J(sub 2)...) associated tidal reductions must be specifically defined in view of particular applications and significant differences between different tidal reduction types. Or one may replace "alpha" by a quantity that is independent of tides, like the geopotential at the geoid, W(sub 0), where temporal changes also are being discussed. The official geodetic reference systems, such as GRS 80 and WGS 84 (revised in 97-form) no longer truly represent reality. A new system GRS 2000 is desired. In the meantime, one is able to define and determine tidal and non-tidal (secular, periodic, aperiodic) variations of some fundamental geodetic parameters. Others are under investigation. New precession and/or nutation formulas to be adopted by IAU in 2000 or later would imply, again, changes in geodetic parameters such as H = hydrostatic flattening. Those and other related consequences are considered. The updated list of "constants" presented in Birmingham in 1999 is given in the appendixes.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2000
- Accession Number
- ADA435898
Entities
People
- Erwin Groten
Organizations
- Technical University of Darmstadt