NATIONAL REPORT OF THE FEDERAL REPUBLIC OF ... - IAG Office

154 Inter-commission committees (ICC) – ICC on Theory (ICCT)
parameterises global density models. The continental hydrosphere
is probably the most investigated physical aspect
in gravity field modelling from space missions. RAMILLIEN
et al. (2004, 2005) present an approach for global time
variations from GRACE. HARNISCH and HARNISCH (2006)
provide the ground truth values from gravimetric data, and
NEUMEYER et al. (2006) combine both terrestrial and space
observations with hydrology models.
BOSCH (2005) reports about errors in the shipborne marine
gravity representation found from GRACE models. The dealiasing
of short-term atmospheric and oceanic gravity
variations from GRACE is published by FLECHTNER et al.
(2006).
The atmosphere effects are in principle reduced from the
geodetic observations by physical models. An approach for
atmoshere pressure reduction from gravimetry is given by
NEUMEYER et al. (2004).
The reliability of the regional models of mass variations
derived from GRACE data processing is discussed by
HORWARTH and DIETRICH (2006), where some errors in the
modelling are demonstrated.
Relativity
As far as relativistic aspects in geodetic modelling are
concerned work concentrated upon three main topics:
– astronomical reference systems,
– dynamical equations of motion and
– relativity tests.
MÜLLER et al. (2007b) present a comprehensive overview
on this subject.
Astronomical reference systems
Of great importance for high precision geodetic modelling
is the introduction of two fundamentally different celestial
reference systems: the Barycentric Celestial Reference
System (BCRS) with coordinate time TCB and the Geocentric
Celestial Reference System (GCRS) with TCG as
coordinate time. SOFFEL et al. (2003) present a detailed
discussion of the BCRS and the GCRS. Here, also the
relativistic forces acting on a satellite are discussed. Special
aspects of local relativistic reference systems are treated
in KLIONER (2004). The problem of representation of the
cosmic expansion in the BCRS is treated in KLIONER and
SOFFEL (2004), SOFFEL and KLIONER (2004a) and in
CARRERA and GIULINI (2006). In these papers it was found
that the influence of the Hubble expansion of the universe
upon physics in the solar system is completely negligible.
Relativistic equations of motion
The problem of relativistic equations of motion of astronomical
bodies has been persued into two different directions.
In a series of papers Xu and collaborators (XU et al.,
2003, 2005) laid the foundation for a relativistic description
of elastic deformable astronomical bodies by means of a
displacement field. However, this formalism is extremely
complex and the relation with observables, e.g., in the field
of Earth's rotation is unclear. Another approach, specially
designed for the problem of Earth's rotation, starts with a
rigidly rotating multipole formalism that is described in
detail in KLIONER et al. (2003). This formalism forms the
basis for the present post-Newtonian approach to improve
Newtonian nutation series. The problem of a relativistic
description of Earth's rotation is discussed in SOFFEL and
KLIONER (2004).
Relativistic tests
Geodetic space techniques such as SLR, LLR or VLBI are
able to provide tests of relativity, both for Special Relativity
and Einstein's theory of gravity. Such tests concern the
Lorentz-invariance, Newton's law of gravity (the 5th force,
G C / G), various forms of the equivalence principle, the
determination of post-Newtonian parameters, the geodetic
precession and Lense-Thirring effects (frame dragging due
to the rotation of the Earth). MÜLLER et al. (2007b) give
an overview over such tests. MÜLLER et al. (2006a, 2006b)
and MÜLLER (2006) discuss the use of LLR data for such
tests of relativity.
References
BOSCH W.: Using the EIGEN-GRACE02S gravity field to investigate
defectiveness of marine gravity data. Springer, IAG
Symposia, Vol. 129, 89-94, 2005.
DREWES H.: Integration von Geometrie und Gravimetrie: Das
Globale Geodätische Observations-System (GGOS). Wiss.
Arb. Fachr. Verm., Univ. Hannover, Nr. 263, 159-168,
2006a.
DREWES H.: Zum Wandel in der Zielsetzung geodätischer Forschung
(The changing objectives in geodetic research).
Zeitschr. für Verm. (131) 292-298, 2006b.
DREWES H.: Science rationale of the Global Geodetic Observing
System (GGOS). Springer, IAG Symposia, Vol. 130, 703-
710, 2007.
CARRERA M., GIULINI D.: On Doppler tracking in cosmological
Spacetimes, Classical and Quantum Gravity (23) 7483,
2006.
FERNANDEZ L.I., SCHUH H., SCHMIDT M., SEITZ F.: Effects of
inter-annual water storage variations on polar motion.
Geophys. J. Int. (169) 12-18, 2007.
FLECHTNER F., SCHMIDT R., MEYER U.: De-aliasing of short-term
atmospheric and oceanic variations for GRACE. Springer
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Boedecker, U. Schreiber (Eds.): Observation of the Earth
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P.: A CHAMP-only gravity field model from kinematic orbits
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GREINER-MAI H., JOCHMANN H., BARTHELMES F., BALLANI L.:
Possible influences of core processes on the Earth's rotation
and the gravity field. J. Geodynamics (36) 343-358, 2003.
HARNISCH G., HARNISCH M.: Hydrological influences in long
gravimetric data series. J. Geodynamics (41) 276-287, 2006.
HECK B.: Problems in the definition of vertical reference frames.
Springer, IAG Symposia, Vol. 127, 164-173, 2004.