Spatial and Temporal Errors in Ers-2 Radial Positioning

Applications involving multi-satellite altimetry (such as from ERS, TOPEX/Poseidon and, in the near future GFO) require that any differences between the altimetric databases are either negligible, resolvable by simple spatial approximations or eliminated by enhancement through dual satellite crossovers. Although orbit error for satellites such as ERS-2 has been considerably reduced over the years it still remains as a major component in the error budget. For ERS-2 with altitude near 800km both gravitational and surface-force mismodelling are significant factors. Several gravity field enhancements such as DGM-E04 [1] and AGM-98 [2] specific for the ERS orbit have been released. These two gravity fields are tuned to ERS through minimisation of single satellite crossovers (SXO) residuals (DGM-E04) or SXO and dual crossovers (DXO) residuals with TOPEX/Poseidon (AGM-98). In this paper we briefly review the AGM-98 orbits for ERS-2. The geographically correlated and anti-correlated error is assessed by using DXO residuals for ascending and descending arcs with a spectral analysis in the Southern Ocean identifying deficiencies of a particular order in the gravity field.