## 5 Conclusions  
Given the uncertainty and error sources in processing raw phase to excess phase and satellite positioning/velocity, a comprehensive reprocessing from different centers using various algorithms is critical to access the structural uncertainty for COSMIC-2 data due to different inversion implementations (also see [51]). In this study, we presented the experiments of the STAR stand-alone procedures to convert the COSMIC-2 carrier phase to the excess phase and convert the excess phase to bending angle profiles. In this study, we analyzed possible errors during each step. We conclude our findings with the following:  
Figure 12: Bending angle comparison with ERA5 as setting and rising profiles for October 2019. The middle lines are mean relative differences, with standard deviation as outer lines. Red is for L2P rising, blue is for L2P setting, and green is for L2C (GPS and GLONASS). Profiles exceeding 10 sigmas at a height between 10 and 45 km have been removed in the comparison. 1. While we use UCAR CDAAC's COSMIC-2 Orbit solution, the receiver clock solution from the Bernese GNSS software is used as input for the excess phase calculation. The Bernese is also used as a tool for GNSS satellite orbital interpolation. However, the receiver clock bias removal in the excess phase is carried out with a single differencing method by differencing with the low rate (1 HZ) POD observations with proper reference satellite observations based on the SNR and zenith angle. We also tested the zero-differencing receiver bias clock removal method. We attributed the STD difference at high altitude from single differencing to large COSMIC-2 receiver clock bias, compared with the COSMIC-1 mission. 2. The comparison results show good agreement between STAR and UCAR excess phase above 10 km, and gradually, the mean difference and standard deviation increase below that level. There are setting and rising bias differences in the excess phase, reflecting differences in the bending angle conversion. 3. The ROPP package has been modified to accommodate the newly calculated COSMIC-2 excess phase from GPS and GLONASS. The results show excellent agreement in the relative bending angle compared with ERA5 simulated bending angle profiles and UCAR CDAAC bending angle profiles. Comparison with ERA5 shows that at the impact height of 10-35 km, the mean relative difference is about \(-0\). \(34\pm 2\). \(69\%\) for GPS non-L2P signals, \(-0\). \(28\pm 3\). \(81\%\) for GPS L2P, and \(-0.09\pm 3.20\%\) for GLONASS. The difference below 8 km gradually increases toward a maximum at 5 km and decreases toward the surface. Above 35 km, there is an increase with altitude in relative bending angle standard deviation. The relative refractivity bears a similar feature with good agreement between 8 km and 35 km. 4. Compared with UCAR, from impact height of 10 km to 35 km, the mean relative difference is less than 0.06%. The standard deviation is usually less than 1.3%, and the difference for GPS L2P is also clearly relatively larger at heights 20-25 km. The GLONASS has a similar performance to the GPS L2C. 5. The L1 SNR value at 80 km is a good indicator of the strength of the GNSS signals transmitted. Comparison among the retrieval quality (comparison with UCAR) and the SNR values shows that the SNR values are correlated with the standard deviations and mean difference comparison with UCAR, implying the SNR impact on the RO bending angle inversion quality. We also found that L2 SNR at the same height (80 km) weakly correlates with the penetration depth only below 600 \(\sigma/v\). 6. While ROPP has been widely used for previous missions reprocessing by ROM SAF and some new missions, such as China's GNOS FY\(-3\) Fengyun mission, some improvements or modifications may be needed for the new mission. The bending angle algorithm difference between ROPP and UCAR can explain most lower troposphere differences.