Referencing airborne gravity measurements with GPS. Combinations of different geodetic techniques are necessary in order to obtain the required stability, consistency and accuracy of the reference frames. Full exploitation of GOCE (Gravity field and steady-state Ocean Circulation Explorer) data will probably rely on ground-based and airborne gravity measurement techniques, as well as other geodetic techniques such as GPS, SLR (Satellite Laser Ranging) and VLBI (Very Long Baseline Interferometry).