NASA's Space Geodesy Project (SGP) uses a variety of space- and land-based techniques to determine the precise shape, position, and orientation of the Earth with respect to the Terrestrial Reference Frame (TRF) and Earth orientation parameters (EOP). This visualization presents a summary of these techniques.
The visualization begins with a shot of natural-looking Earth, then transitions to a view that shows the orbital components of the SGP, which include global navigation satellite systems (GNSS), satellite laser ranging (SLR) and Doppler Orbitography by Radiopositioning Integrated on Satellite (DORIS).
The view then moves to the surface of the Earth, showing the positions and direction of the motion of ground stations as measured by these techniques, as well by ground-based very long baseline interferometry (VLBI), which uses the radio emissions of distant quasars to determine geodetic measurements.
We then zoom into the center of the Earth to show the consequence of these surface motions: the movement of the geocenter, which these techniques can determine to within millimeters.