High Resolution Earth Gravity Field Models from Satellite and Tracking Data, Sea Surface Heights and Gravity Anomalies, Spherical Harmonic Representation

The high resolution Earth gravity field models, produced by GFZ,
contain spherical harmonic coefficients complete to degree and order
360. A-priori information is taken from long wavelength gravity field
GRIM (see other GFZ data set descriptions). High frequency
determination is based on both surface gravity and ocean geoid
heights. Surface gravity is corrected for topographic and atmospheric
effects. Ocean geoid heights are derived from mean sea surface height
models determined from altimeter data (e.g. ERS-1, ERS-2, Topex,
Geosat, Seasat, Geos3 and others). They are corrected for sea surface
topography and permanent tidal deformation.

The estimation of the 360 field is based on a least squares harmonic
analysis.

With globally distributed, equally spaced data sets, the normal
equation system decomposes to block diagonal structure. Undefined data
are successively substituted by block mean values from intermediate
results.