Improvements in High Resolution Gravity Field Modeling at GFZ
Global high-degree gravity field models, complete to degree 360 have been computed by two different groups. While the Ohio State University approach is based since many years on a combination of complete long wavelength normal equations with a diagonal system for the high degrees, at GFZ the block-diagonal least squares technique was used for estimation of the complete coefficient series. For the new GFZ models as well as for the new American EGM96 model, an improved strategy based on a combination of complete normals for the long wavelengths, with block-diagonals for the high frequencies was implemented. In addition some new mean gravity data for Russia, better information from altimetry over the oceans, and an improved data preparation scheme was introduced. Different new 360 gravity field solutions were computed by this scheme. Comparisons to the OSU91A model and the GFZ95A model show some improvements with respect to the previous solutions, which can be addressed nearly completely to the new estimation technique. Further studies are required for the combination of different data types (e.g gravity anomalies and geoid heights) in one solution, and for a further improvement of the modeling towards a complete and strong least squares solution for the 360 spherical harmonic series.
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