  Due to the accuracy now reached by space geodetic techniques, and also
considering some modelisations, the temporal variations of some Earth Gravity
Field coefficients can be determined. They are due to Earth oceanic and solid
tides, as well as geophysical reservoirs masses displacements. They can be
related to the variations in the Earth's orientation parameters (through the
inertia tensor). Then, we can try to improve our knowledge of the Earth
Rotation with those space measurements of the Gravity variations. We have
undertaken such a study, using data obtained with the combination of space
geodetic techniques. In particular, we use CHAMP data that are more sensitive
to such variations and that complete the ones already accumulated (for example
with Starlette and LAGEOS I). In this first approach, we focus on the Earth
precession nutation, trying to refine it by taking into account the temporal
variations of the Earth dynamical flattening. The goal is mainly to understand
how Geodesy can influence this field of science. Like this, we will be able to
compare our computation with up to date determinations of precession nutation.
