The Determination of the External Gravity Field of the Earth from Observations of Artificial Satellites

The principles and results of the determination of the external gravity field of the Earth from the motions of artificial satellites are reviewed. Since the general ideas and results are by now widely understood, most attention will be given to problems that still remain in the theory and its application. These will include: the functional form in which the external potential is expressed; exact solutions in the theory of orbits; the statistical difficulties of deriving coefficients of spherical harmonic components of the field from observations of a restricted number of satellites; current estimates of the harmonic coefficients of the external field; the theory of the near field and comparisons between satellite results and surface measurements of gravity; and the bearing of the results on the physical state of the Earth’s interior. 1