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Time - Earth Gravitational Model

The European Gravimetric Geoid (Denker and Torge 1998, Denker 1998) is available to the scientific community, representing a milestone in the development of the European Geoid. Unfortunateley, the published CD-rom does not contain the free air gravity anomalies which have been used for the computation of EGG97. The computation of high resolution free air gravity anomalies from the published EGG97 quasi geoid heights using an ultra high degree geopotential model is therefore subject of this paper.
Using integral formulas in an iterative algorithm, three very high degree geopotential models have been computed from EGG97: GPM3E97C to degree 720, GPM3E97B to degree 1080, and GPM3E97A to degree 1800. For GPM3E97A, about 800000 mean 5' x 5' quasi geoid heights from EGG97 have been used inside Europe (25 deg < lat < 77 deg, -35.0 deg < lon < 67.4 deg) and about 8 million mean 5' x 5' quasi geoid heights computed from geopotential model EGM96 to degree 360 have been used outside Europe. The rms discrepancy between the input quasi geoid heights and quasi geoid heights computed from GPM3E97A is 0.005 m with 0.295 m maximum discrepancy (this results from the lack of resolution of GPM3E97A compared to EGG97

Welcome to the official webpage of the NASA and NIMA joint geopotential model, EGM96. EGM96 is a spherical harmonic model of the Earth's gravitational potential complete to degree and order 360. On this website, we summarize the development of this model, and include information presented at the International Symposium on Gravity, Geoid, and Marine Geodesy, Tokyo, Japan, September 30 - October 4, 1996.
EGM96 The NASA GSFC and NIMA Joint Geopotential Model

Report - Presented at IUGG99, IAG Section III "Determination of the Gravity Field", Birmingham, July 18 - 30, 1999

Goddard Space Flight Center contact: E. Pavlis
GFZ: GeoForschungsZentrum), Potsdam, Germany contact: P. Schwintzer
GRGS: Groupe de Recherche de Geodesie Spatial) of CNES, the French space agency contact: R. Biancale
CSR: Center of Space Research, Texas University, Austin, Texas contact: C.K.Shum
ssg3167 - This paper summarizes the activities and achievements of the IAG Special Study Group (SSG) 3.167: "Regional Land and Marine Geoid Modelling", which was established by the XXIth General Assembly of IAG held in Boulder, Colorado, USA, July 3-14, 1995. SSG3.165 Global Gravity Field Determination and Evaluation Chairman: N. Pavlis

The Special Commission will act as a forum of discussion and information related to these various missions. Besides these topics the Special Commission should also act as a brain pool for ideas of future developments in gravity field research. This encompasses not only applications to various fields of geo sciences but also developments of future satellite borne techniques to measure the gravity field.
Satellite gradiometry is superior for obtaining high spatial resolution from a moderate mission length. A recent study showed that increase of measurement precision or decrease of altitude results in a clear gain of spatial resolution in case of SGG, while this effect is very moderate in case of SST. A SGG mission like GOCE is superior in the short wavelengths parts of the gravity field up to a spherical harmonics degree of 250. The results of a mission like GOCE start to be better than those of a low-low SST mission from degree 60 to 80 on. A high-low SST mission like CHAMP can provide an improvement in the knowledge of the gravity field of approximately one order of magnitude over present models for wavelengths between 400 to 2000km.

gruen_161.html - Gradiometry - an Inverse Problem in Modern Satellite Geodesy, Freeden, W., Schneider, F., Schreiner, M.

Satellite gradiometry and its instrumentation is an ultra-sensitive detection technique of the space gravitational gradient (i.e. the Hesse tensor of the gravitational potential). Gradeometry will be of great significance in inertial navigation, gravity survey, geodynamics and earthquake prediction research. In this paper, satellite gradiometry formulated as an inverse problem of satellite geodesy is discussed from two mathematical aspects: Firstly, satellite gradiometry is considered as a continuous problem of harmonic downward continuation. The space-borne gravity gradients are assumed to be known continuously over the satellite (orbit) surface. Our purpose is to specify sufficient conditions under which uniqueness and existence can be guaranteed.

This model of the Earth' gravitational filed was developed in a collaborative effort of the NASA Goddard Space Flight Center, the National Imagery and Mapping Agency (NIMA), and the Ohio State University. It is based on surface gravity data, altimeter-derived gravity anomalies from ERS-1 and from GEOSAT, extensive satellite tracking data (GPS, TDRSS, DORIS, TRANET), and direct altimeter ranges from TOPEX/POSEIDON, ERS-1, and GEOSAT. The spherical harmonics model includes terms up to degree 360.
The predecessor models are the OSU-91A (Rapp et al., 1991) and the JGM-2 (Nerem et al., 1994) models.
Please contact : F.G. Lemoine, NASA/GSFC, Laboratory for Terrestrial Physics,
Greenbelt, Maryland 20771, (301) 286-2460, flemoine@ares.gsfc.nasa.gov

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