Gravity Research Missions reviewed in light of the indirect ocean tide potential.

Abstract

In the last 15 years a number of proposals have been made for the realization of a dedicated gravity research mission, hereafter referred to as a GRM. We deliberately avoid a lengthy summary of all the different concepts. It is sufficient to mention that gravity gradiometry and tracking of the orbiter have been proposed for mapping the detailed structures of the Earth’s gravitational field. The current shortcomings in global gravity models are still the main motivation for flying a gravity research mission. Terrestrial data is too heterogeneous with still many areas not sufficiently covered, cf. Rapp (1993). Airborne gravimetry, cf. (Brozena,1991), may help to map poorly accessible areas but is still far from filling in the gaps in current terrestrial gravity datasets. Satellite altimetry is only effective over the oceans and rather helpful for mapping the detailed structures of the marine gravity field. For the longer wavelengths, ie. up to degree and order 10 or so, altimetry can distinguish between the quasi stationary sea topography and the geoid, thereafter it is hardly possible to separate both fields, cf. (Schrama,1989). The technique that comes closest to what could be called a global gravity model is based on the concept of tracking spacecrafts which fundamentally provides use with the long wavelength features of the field, cf. (Tapley,1989). Satellite gravity models still show a heterogeneous error pattern which is especially the case where terrestrial gravity data and direct satellite altimeter data are included in the solution, cf. (Tsaoussi and Koblinski,1994).