Local and global gravity field representation

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Abstract
Gravity fields applied in geodesy are usually built up by (1) a global satellite (low harmonics) part obtained from altimetry and/or differential orbit improvement (in the future, satellite to satellite tracking techniques will also contribute), (2) a regional part obtained from conventional terrestrial material, and (3) a local part of ±1‐mGal accuracy. Whenever four‐dimensional considerations are of interest, ±0.001‐mGal accuracy is necessary. The combination of these parts is considered; attention is also paid to the zero‐degree term in view of very accurate modern absolute measurements of gravity. Integral equation solutions dominated by kernel functions such asl−nas well as collocation formulas lend themselves to useful combinations of high‐precision regional and low‐precision global parts where many difficulties arise in practical applications. But no ideal method is available in order to overcome deficient knowledge of the gravity field. Detailed applications of Stokes‐ and Poisson‐type solutions are discussed. In spite of the fact that a lot of local information is averaged out because of its random behavior, valuable information on systematic effects gets lost unless local parameters are incorporated. Model considerations are based on Kaula’s rule of thumb for high harmonics.

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