Monday, October 09, 2006

Earth's Future in Planetary Observation

On March 31, 2006 the high-resolution gravity field model EIGEN-GL04C has been released. This model is a combination of GRACE and LAGEOS mission plus 0.5 x 0.5 degrees gravimetry and altimetry surface data and is complete to degree and order 360 in terms of spherical harmonic coefficients.

High-resolution combination gravity models are essential for all applications where a precise knowledge of the static gravity potential and its gradients is needed in the medium and short wavelength spectrum. Typical examples are precise orbit determination of geodetic and altimeter satellites or the study of the Earth's crust and mantle mass distribution.

But, various geodetic and altimeter applications request also a pure satellite-only gravity model. As an example, the ocean dynamic topography and the derived geostrophic surface currents, both derived from altimeter measurements and an oceanic geoid, would be strongly correlated with the mean sea surface height model used to derive terrestrial gravity data for the combination model.

Therefore, the satellite-only part of EIGEN-GL04C is provided here as EIGEN-GL04S1. The contributing GRACE and Lageos data are already described in the EIGEN-GL04C description. The satellite-only model has been derived from EIGEN-GL04C by reduction of the terrestrial normal equation system and is complete up to degree and order 150.

Many if interested just have to do a search on Grace in this Bloggery to know the efforts gravitational research has gone to develope the views we have of earth from that magnificent pearl to the dramatic realizations of it's covering above.

ArcGP grid, January 2006 (mGal). Some ERS and ICESat altimetry has been used to fill in some data gaps/errors in the original compilation. (units mGal).Credits: ArcGICE Study Group
A combination of new satellite-derived datasets is providing an exciting opportunity to peer through the sea-ice cover to study circulation patterns in the Arctic Ocean (Forsberg et al., 2006). A better understanding of what's going on beneath the ice will, in turn, lead to a more accurate interpretation of sea-ice thickness data from CryoSat-2.

The new estimates of Arctic Ocean mean dynamic topography have been compiled through a combination of satellite altimetry data from ERS, Envisat and ICESat, and a revised geoid model based on surface, submarine, airborne and satellite gravity field data from the US-German GRACE mission.

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