Links of the space geodesy techniques are listed below:

Several Observation Techniques are used to observe the geodetic parameters of the Earth and each of them provide different parameter types.

GPS describes satellite and moon orbits for the Celestrial Reference Frame (CRF), Earth Rotation Parameters (Nutation rates, LOD, Polar motion), Station positions for the TRF, as well as Geocenter and Low-degree Gravity fields and Atmosphere parameters of the Troposphere and the Ionosphere.

DORIS provide all of the parameters provided by GPS.

SLR determines the same parameters as DORIS and GPS, but without atmospheric conditions.

VLBI is the only technique that determines Quasar positions for the CRF, nutation, and UT1-UTC of the Earth Rotation Parameters. In this last case, this observation technique is indispensable. On the other hand, VLBI measures neither satellite or moon orbits nor influences of the gravity field.
Because of the different parameter determination, the techniques have to be connected by co-locations. Learn more here

View the parameter statistics of the space techniques

Connection of the techniques