Page - 93 - in Contributions to GRACE Gravity Field Recovery - Improvements in Dynamic Orbit Integration, Stochastic Modelling of the Antenna Offset Correction, and Co-Estimation of Satellite Orientations

7.3.4 Application to real GRACE data In addition to the simulations discussed in sections 7.3.2 and 7.3.3 the dynamic orbit computation was also carried out with real data in the context of the ITSG-Grace2016 gravity field solutions (Klinger, Mayer-Gu¨rr, et al., 2016; Mayer-Gu¨rr, Behzadpour, et al., 2016). In addition to the static GOCO05s potential, these orbits now include accelerations due to conservative forces from several more background models (see ta- ble 6.1 for details). Further, direct observations of accelerations due to non-conservative forces from the GRACE accelerometers are included in the integration. The orbits are fit to GRACE ll-SST and hl-SST observations as described in section 6.3. Figure 7.6 shows that neither of the Kepler-parametrised configurations (pink and green) shows any improvement over the implementation not employing a reference acceleration (brown). For real data, the superiority of the best-fit reference trajectory is confirmed when studying the configurations using equinoctial elements. Neither of the equinoctial configurations (purple and orange) show the large drop in quality when switching to real data that was observed in the Kepler-parametrised configurations (pink and green). The increase in residual power at one cycle per revolution is still present in all solutions, but the magnitude remains smallest for the best-fit equinoctial configuration (orange). Overall, the best-fit trajectory parametrised in equinoctial elements (orange) is superior to the other configurations in the same way as could be seen in the simulated data. The comparative impact of this improved methodology is significantly larger for real data than could be expected from the less complex data used in the simulations of section 7.3.3. 0.1 1 10 100 Frequency [mHz] 10−9 10−8 10−7 10−6 10−5 10−4 10−3 Figure 7.6: Real data. In-Track coordinate differences after convergence for real GRACE orbits. Colours denoting the configurations are the same as in figs. 7.4 and 7.5. 7.3 Results 93