A 20x20 QSST was adjusted simultaneously with the geopotential coefficients in EGM96, and is depicted below. The separation between the altimetric surface, defined by the ERS-1 and TOPEX altimeter data, and the geoid is accomplished through (1) the incorporation of marine gravity data in the surface gravity normals, and (2) the imposition of a power law constraint on the spectrum of the QSST, where this power law was derived from a fit to spherical harmonic coefficients derived from output of the POCM_4B ocean circulation model. We solve for a single QSST for both TOPEX, and ERS-1 , since the two sets of data are temporally coincident. Furthermore, the weight for ERS-1 was selected such that the TOPEX derived QSST would not change over the TOPEX domain (+/- 66 deg latitude) by more than 2 cm. In addition to the quasi-static terms of the sea surface topography, a time variable SST to 10x10, consisting of annual and semiannual terms was also solved for.
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