The gravity potential of a central body only represents the static part of the gravitational acceleration acting on a satellite. There are, however, additional gravity-related effects due to tides that can be important for precise applications. Several tidal effects can be distinguished (see [RD.1]):
• Solid Earth tides associated with the deformations of the Earth’s body under the gravitational effects of Sun and Moon and leading to complicated variations in the geopotential coefficients.
• Ocean tides, associated with the displacements of the ocean water masses under the effect of solar and lunar tides. The water displacements in turn modify the geopotential in complicated variational patterns.
• The permanent tide, which is a non-zero constant component of the above tides which nonetheless is not considered part of the static geopotential.
• Pole tides, which are due to the centrifugal effects of polar motion, which in turn is the movement of the Earth’s body axis relative to the instantaneous axis of rotation.