## 3 Verification of the STAR-Derived Excess Phase and Bending Angle Profiles
### Comparisons to UCAR Bending Angle for Different SNR Groups  
[PERSON] et al. [2] showed that the COSMIC-2 bending angle penetration depth is strongly correlated with the L1 SNR values at about 80 km altitude for GPS and GLONASS signals. The profiles can have a lower penetration depth approaching the surface with larger SNR values. Here, we analyze the SNR effects on our data comparison with UCAR results and examine how the SNRs affect RO processing. We adopted the UCAR convention, which uses SNR values at a high altitude of 80 km as references. In excess phase processing, the SNRs are correlated with the cycle slips. The larger the SNR values, the cycle slips can be quickly restored. At a low altitude below 10 km, cycle slips are strongly corrected with SNR values below 300 \(v/v\). Figure 8a compares the STAR processed bending angle with UCAR processed bending angle under different L1 SNR value categories. Clearly, the larger the SNR values, the better the comparison looks. There are relatively more significant standard deviations and larger wiggling structures in the bending angle difference/standard deviation profiles with lower SNR values. The standard deviation is the smallest for a group with SNR values >2000 \(v/v\), both at high altitudes and near the surface. Additionally, the bias in this group is smaller, below 10 km, than in other groups. The worst case is for the lowest SNR groups, less than 500 \(v/v\), with a more significant standard deviation and the most considerable difference below 10 km. The difference below 10 km for a group with <500 \(v/v\) indicates bending angle difference departure from UCAR occurs higher than in other groups, implying the SNRs values have impacted the penetration depth. Figure 7: ROPP inverted bending angle profile comparison with UCAR bending angle profiles using (**a**) STAR derived excess phase, (**b**) UCAR provided excess phase, and (**c**) profile differences statistics (STAR). The significant variations of the SNR, as shown in Figure 8, can be associated with fluctuations in the excess phase. In Figure 3j-l, larger SNRs usually have fewer oscillations at the beginning (end) of setting (rising) occultation. The lower the SNR (at 80 km) is, the more quickly it approaches the large oscillation (large Scintillation index) region before becoming too weak to be used. Lower SNR values at 80 km mean the SNRs decrease rapidly over time. [PERSON] [50] has studied the SNR values with the RO inversion quality. There is no significant correlation between the SNR values and the bending angle quality unless the SNR value is too low and the bending angle profile cannot be correctly inverted. A detailed look at SNR values at the high altitude and the lower scintillation index may explain the difference since the SNR values can affect the cycle slip detection, especially the scintillation index, rather than the SNR values at high altitude. The COSMIC-2 bending angle profiles penetration depth correlates with SNR values in the operational datasets, proving that larger SNRs can penetrate deeper [2]. This study can regenerate this correlation using the operational UCAR bending angle dataset and the STAR-generated bending angle profiles. While the correlation holds, a near-constant bias exists in the penetration depth across all SNR values between UCAR and STAR profiles (Figure 8b,c). This bias is around 0.55 km in mean sea level height and 0.4 km in impact height. While the excess phase profiles are generally the same in time (and hence straight-line height), the inversion to bending angle from modified ROPP determines the penetration depth. We also compared the correlation of penetration depth with L2 SNRs. Although a general correlation holds that larger SNRs correspond to deeper penetration depth, SNR L2 and penetration depth are less correlated with L2 SNR values higher than 600 \(v/v\). This may be related to the SNR cut-off values used differently in this ROPP configuration and UCAR's bending angle algorithm.