## 4 Results and Discussion
### Orbit Comparison  
As outlined in Section 3.5, the inter-comparison of the different precise orbit products allows for a realistic assessment of the accuracy and might reveal possible systematic errors. Figure 4 shows daily 3D-RMS differences in position between the WEGC-BC solution and externally provided orbits. The corresponding position and velocity differences in radial, along-track, and cross-track directions are summarized in Table 3. When comparing the different orbit solutions overall best agreement is found for the comparison of WEGC-BC and WEGC-BI. This can be expected from the fact that in this case the differences are simply governed by the impact of different GNSS orbit, clock, and associated EOP data while using the same POD software with consistent processing settings. For all missions the RMS of the daily 3D-RMS series does not exceed 1.4 cm. However, a single day for GRACE-A of about 4 cm difference can be found. The WEGC-NC solution generally compares at a similar level to WEGC-BC as the external solutions, with the exception of decreased differences found between WEGC-BC and AIUB for CHAMP. Figure 3: Propagated random uncertainty estimates (based on propagating standard errors) from Bernese for the constellation of GPS satellites on an example day (12 March, 2016), for position (**left**) and velocity (**right**), for the radial, along-track, and cross-track components. Coverage factor of 2 applied. _CHAMP._ For the CHAMP mission best agreement is found with AIUB with an RMS of about 1.8 cm (note: 3 days from AIUB are missing in the provided data). Solutions from WEGC-NC, EUMETSAT, and UCAR compare at a similar level, where the comparison to UCAR features a slightly better comparison with an RMS of about 4.0 cm. Individual days still exhibit differences above the 5 cm threshold. _GRACE._ Differences from orbit comparison for GRACE-A presented are higher than results from space-geodetic applications, such as gravity field recovery [46]. However, results from those applications are based on screened observation files (available from JPL) where the clock error was detrended and altered substantially, compared to the raw observation files available at CDAAC. As already outlined in Section 3.1, dealing with such large clock trends poses challenges in handling the data by the POD software packages. This leads to comparison results indicating a slightly degraded quality but still within the conservative bounds for RO. Note that while the WEGC-NC and AIUB solutions are based on these screened L1B products, all other solutions are based on the raw L1A observation data. Figure 4: Daily 3D-root-mean-squared (RMS) orbit differences between the WEGC-Bernese (CODE) primary solution and WEGC-Bernese (JPL), WEGC-Napeos, UCAR, EUMETSAT, and AIUB orbit solutions for: **(a)** CHAMP and **(b)** GRACE-A from July to September 2008, and **(c)** Metop-A and **(d)** Metop-B for July to September 2013. Gray shading in the Metop-A/B panels indicates three excluded days where an orbit maneuver took place (Metop-A: 2013-09-04; Metop-B: 2013-08-07) or satellite attitude from CDAAC is missing (2013-09-15, 2013-09-16). Rare outliers exceeding 20 cm in 3D-RMS difference (10 days total for all four satellites) have been disregarded for the calculation of the overall RMS noted as part of the legend (in units cm). The number of total days included in the calculation for each orbit solution is denoted by “\(n\)”. In Figure 4b increased values of comparison in September 2008 and missing days end of August for UCAR can be seen for GRACE-A, which is in accordance with periods when the satellite clock error is peaking before it is reset. Also, increased along-track differences (Table 3) compared to solutions based on pre-screened RINEX suggest a shift in time. In particular for the comparison of the primary solution, and the one by AIUB, the use of different low-level input data leads to increased differences for GRACE-A (4.3 cm) compared to the same comparison conducted for CHAMP (1.8 cm).