Tide-Free System

The tide-free system (also called non-tidal system) removes both the direct tidal potential and the associated permanent deformation of the Earth. In this system, the permanent tidal effects are entirely excluded.

In geodesy, the tide-free system was historically used in some gravity field models and theoretical formulations. However, it differs from the zero-tide convention adopted for modern terrestrial reference frames, and careful transformations are required when combining products defined in different tide systems.