## 1 Introduction
With different dynamic models, clock bias removal methods, and the arc-integration lengths of the POD processing, the orbital solution can vary from a few centimeters (cm) to more than 10 cm, which will lead to extra bending angle estimate uncertainty. The operational COSMIC-2 POD calculation is based on the short-arc (around one hour) solution. Because of the different clock systems and the signal frequencies among GPS, GLONASS, and GALILEO, the quality of COSMIC-2 LEO POD solutions may also be different [27]. The POD for the COSMIC-2 mission post-processing requirement is within 10 cm for position and 0.1 mm/s for velocity. 2. Conversion of the COSMIC-2 carrier phase to excess phases The different procedures for clock bias removal, the direct geometric range removal, and the antenna phase center position in the ECI Coordinate System may also introduce uncertainty in the excess phase calculations (see [25; 28]). The different phase models may also lead to excess phase calculation errors. For example, the open-loop phase model for the excess phase cycle slip removal for receivers with open-loop tracking may lead to extra bending angle uncertainties in the lower troposphere [29]. [PERSON] et al. [25] showed that the single and double-difference clock removal methods for COSMIC-1 with different sampling intervals in excess phase could yield about 1% fractional refractivity difference at high altitudes. Due to different transmitter/receiver clock removal methods and the open-loop phase model, we must carefully quantify the COSMIC-2 bending angle and refractivity retrieval uncertainties. 3. Inversion of excess phase to bending angle Different implementations of excess phase to the bending angle can also introduce bending angle retrieval uncertainty. [PERSON] et al. [30] compared the reprocessed RO products of different missions, including Meteorological Operational satellite (Metop) GNSS Receiver for Atmospheric Sounder (GRAS), Challenging Ministatellite Payload (CHAMP), Gravity Recovery and Climate Experiment (GRACE), and COSMIC-1, with different processing centers. The results showed that the mean inter-center bending angle fractional differences were minimal between 10 and 30 km impact height, less than 0.1% for all missions, and can be more than 1% above 50 km for CHAMP. [PERSON] and [PERSON] [31] compared the Metop-A/B GRAS data reprocessed by UCAR and Radio Occultation Meteorology Satellite Application Facilities (ROM SAF) and found that ROM SAF processed bending angle has a negative difference (ROM SAF minus UCAR) even after strict quality control, especially near the surface over the tropical area. [PERSON] et al. [32] compared their bending angle results with UCAR (using the same excess phase). The bending angle is consistent with a 0.1% mean difference above impact height of 5 km from different bending angle algorithms. These inter-center comparison results are critical for understanding the error magnitude for other reprocessing procedures and how the uncertainty propagates to the downstream products. For COSMIC-2, [PERSON] et al. [33] converted the UCAR operational excess phase to bending angle using the full spectrum inversion method. The study showed that the bending angle profiles agree well with UCAR and the European Center for Medium-range Weather Forecast (ECMWF) reanalysis version 5 (ERA5) with less than the 0.1% mean difference between 8 and 40 km altitude and a standard deviation (STD) range of 1.4-2.3%. The current near-real-time COSMIC-2 products are processed by UCAR COSMIC Data Analysis and Archive Center (CDAAC) [34]. The quality of the UCAR processed COSMIC-2 data has been assessed in terms of precision, stability, and accuracy [1]. The STAR's L1a-L1b processing is also briefly outlined [35]. However, how the L1a-L1b processing, including implementing LEO satellite POD calculation and converting the COSMIC-2 carrier phase to excess phases, will affect the COSMIC-2 bending angel profiles was not explicitly quantified.