Gravity Field Estimation from Future Space Missions: TOPEX/POSEIDON, Gravity Probe B, and Aristoteles

Abstract

Accurate knowledge of the gravity field is a firm requirement in any study of Planet Earth. From the long wavelength signal of the mantle processes to the very local features of the continental lithosphere, gravity is a driving and shaping force whose accurate determination has been a major scientific goal for centuries. Space techniques have so far demonstrated their superiority in the global mapping of the gravity field based on ground tracking and altimeter data mostly. Proliferation of global tracking of geopotential missions from the Global Positioning System (GPS) satellite constellation has added a new and very powerful source of gravity information to be combined with the primary observations (altimeter data, laser ranging, gradiometry) for gravity field determination to unprecedented accuracies. Numerical and analytical simulation studies of the upcoming geophysically relevant missions that will most likely cany GPS receivers, indicate significant improvements in the accuracy as well as the resolution of the gravity field. TOPEX will improve by some two orders of magnitude the long wavelength part (to degree ~20), while GP-B will contribute in the long as well as medium wavelength part of the spectrum (up to degree ~60). The gradiometer measurements on ARISTOTELES will contribute in the medium and short wavelength regions (from degree ~30 up); GPS tracking of the spacecraft though will provide additional information for the long wavelength gravity and will help resolve it to accuracies comparable to those obtained from GP-B. With the mean rms coefficient error per degree kept below 10⁻¹⁰ geophysical signals such as the post-glacial rebound, tidal variations, and secular and periodic variations of the zonal field rise above the noise level and become readily observable processes.