## 5 Conclusions  
Climate benchmark data derived from GNSS RO require accurate and robust POD of the GNSS transmitter and LEO receiver satellites taking part in an occultation measurement. In this paper we presented a novel setup for routine quality assessment and uncertainty estimation of the daily LEO receiver satellite orbits independent from external validation sources. The GNSS orbit uncertainty estimates were complemented by building on existing error estimates from the GNSS community. As part of WEGC's rops we provide estimates of systematic and random uncertainties associated with the orbit determination, deduced from different LEO POD runs, SLR measurements, and formal uncertainty analysis. We focused on the validation of the WEGC primary orbit solution, which is chosen to deliver the receiver orbit positions, velocities, and clock estimates for subsequent RO processing and the derivation of atmospheric profiles of ECVs. Figure 6: Daily position and velocity uncertainty estimates for the WEGC-Bernese (CODE) primary solution for **(a)** CHAMP and **(b)** GRACE-A from July to September 2008, and for **(c)** Metop-A, **(d)** Metop-B, **(e)** GPS-23, and **(f)** GPS-24 for July to September 2013. The “raw systematic” values denote the estimated systematic uncertainties before applying the conservative bound value (\(u_{\text{CB}}\)) while the “total systematic” values show the estimates including this low-bounding value. For the performance assessment of the extended POD setup we investigated 3 representative months of data from July to September in 2008 (CHAMP and GRACE-A) and 2013 (Metop-A/B). The comparison of the WEGC primary solution with orbit solutions from internal control runs showed reliable agreement within 5 cm in position and 0.05 mm/s in velocity, which is the target threshold specification set for high-quality orbit products for RO climate applications. This threshold is also satisfied for most days in an inter-comparison with orbits from the external providers UCAR, EUMETSAT, and AIUB. SLR residuals using selected high-quality ground stations, available and used for CHAMP and GRACE-A, exhibited a mean and standard deviation of \(-0.15\pm 1.83\) cm and \(0.17\pm 2.88\) cm, respectively, well within the target ranges. Interchange of the GNSS orbit data used with one POD software, without altering the processing setup, shows relatively small differences in the orbit inter-comparison. This suggests that different POD software implementations and configuration settings are more relevant to the uncertainty estimation than potential quality differences in the GNSS orbit data products. Overall, the uncertainty estimates are found to be within the specified target thresholds for 92% of the days considered. The remaining 8% of days exhibit higher uncertainties of order 5 to 15 cm. This is still adequate for RO processing and at the same time results in somewhat increased uncertainty estimates of the derived ECVs, after propagation through the rOPS retrieval chain. These results suggest a high processing standard and robustness, shared among all processing centers, and indicate rOPS POD system readiness for long-term climate reprocessing of RO data records from CHAMP, GRACE, and the Metop satellite series. Further modifications of the observation geometry system of rOPS may be applied in future with the inclusion of other RO missions and enhancements of the basic uncertainty estimation. As another important RO mission, we currently integrate POD processing of FORMOSAT-3/COSMIC (Formosa Satellite mission-3/Constellation Observing System for Meteorology, Ionosphere, and Climate) [103]. This will show the retrieval performance implications of the rOPS POD setup for the case of overall degraded POD quality (about 15-25 cm position uncertainties [90]), due to less favorable attitude behavior of the rather small COSMIC spacecraft and restrictions in processing observations from two POD antennas.