The Earth as a whole responses to external forces as an elastic body. Putting additional mass on the Earth's surface causes crust deformation. Changes of loading mass result in variable displacements of Earth's surface. If not properly accounted such variations distort precise geodetic measurements. Periodic loading causes harmonic site position variations which are detected in analysis of VLBI observations and other space geodesy techniques.

Mass loading has four constituents: 1) changes of air mass that results in change of surface air pressure; 2) change in ocean level due to lunar and solar tides; 3) change of ocean level due to wind and atmospheric pressure; 4) change in soil moisture. These four loading are to be taken into account in processing space geodetic data when precision better 1 cm is required.

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