ERS-2 orbit computations using CHAMP- or GRACE-based gravity field models

The CHAMP and GRACE satellites are producing global gravity field models with unprecedented precision and quality. It is anticipated that the gravity field induced orbit errors are reduced significantly when using these models in precise orbit computation of low flying satellites. The ERS-2 satellite is selected here to serve as an example for recomputation of its orbit using CHAMP- or GRACE-based gravity field models to test their accuracy using an external method. A data period is selected covering January 1996-December 1998, including a large data set of Satellite Laser Ranging (SLR), Precise Range and Range-rate Equipment (PRARE) and single- and dual-satellite (with TOPEX) altimeter crossover observations. The accuracy of the newly computed orbits is assessed by analyzing tracking data and altimeter crossover observation residuals, thereby giving an independent indication of the quality of the new gravity field models. It is indicated that using the best CHAMP- or GRACE-based gravity field models, a radial orbit accuracy improvement of a few cm is possible, which is consistent with the claimed accuracy level using the best pre-launch gravity field models.