A Review of Satellite-Derived Figures of the Geoid and Their Geophysical Significance

Abstract

One of the major geodetic results that has come out of the satellite tracking program, in addition to the revision of the degree of polar flattening for the Earth, is that the Earth is characterized by a series of previously undefined geoidal highs and lows. As these cannot be correlated with the surface mass distribution defined by the continents and ocean basins, they presumably are related to regional variations in gravity resulting from the mass distributions within the Earth. That they may have other geophysical as well as geological significance has been proposed by various investigators (Lee and MacDonald, 1963; Wang, 1963 ; Runcorn, 1964 ; Baussus, 1960 ; Vogel, 1960; Scheffer, 1966; Strange, 1966) . However, the geoidal pattern defined by different investigators has not been totally consistent in that there are differences both in basic pattern and in magnitude of the geoidal undulations. There has also been an evolutionary trend in the complexity of the geoidal pattern defined. This change in overall pattern, as well as the differences in pattern obtained by different investigators, can be related to the sampling of data used (number of satellites and their orbital elements as well as number and distribution of tracking stations); the type of tracking data used (optical versus electronic doppler observations); the parameters of the reference ellipsoid used (particularly the degree of polar flattening ) ; the degree of fit as represented by the order and degree of the coefficient terms and their derived values; and the combinations of data used, such as satellite plus surface gravity observations. There have also been studies based entirely on surface gravity observations which have been influenced in various degrees by the assumptions made by different investigators for the surface gravity field where there are no observational data.