Knowledge of the Earth’s gravity field, as well
as its temporal variation, is of prime importance
for Geodesy, Navigation, Geophysics,
Geodynamics, and related disciplines. We have
noted in the definition of Geodesy that the gravity
field is affected by many terrestrial as well
as extraterrestrial phenomena. The observation
of the gravity field, and the analysis and
modelling of these observations, can help us
to answer important questions such as: