# Phase Center Corrections for BDS IGSO and MEO Satellites in IGb14 and IGSR3 Frame
## 5 Conclusions  
In this contribution, one year of undifferenced dual-frequency (B1I and B3I) measurement data from global tracking networks of MGEX and iGMAS were analyzed to evaluate whether the terrestrial scale derived from released BDS PCOs is consistent with that obtained with released Galileo PCOs, and to obtain the PCO estimates for BDS in IGb14 and IGSR3 frame for preparing BDS for IGS repro3 and legacy analysis. From the analysis of the PCV estimates, it was found that the C10 satellite shows a different PCV pattern with respect to its counterparts. Moreover, there was a lower repeatability for C35-C37 satellites, and the main reason was the small number of stations which can track these satellites. However, for other satellites, their PCV shows quite good consistency (bellow 2.0 mm). Hence, the satellite-block-specific PCV estimates were derived. From the analysis of the PCOs estimates, we focus on the impacts of scale on the PCO estimates. The Z-PCO shifts about \(-\)414.9 mm, and \(-\)174.0 mm for BDS IGSO and MEO satellites, when the IGSR3 frame was used instead of IGb14. The \(-\)174.0 mm Z-PCO shifts equals about +1.27 ppb at the height (about 21200 km) of BDS MEO satellites, which is quite consistent with the scale bias +1.24 ppb when IGb14 was transformed to IGSR3. To verify the influences and reliability of the PCOs and PCVs estimates, we reprocessed the data with three different schemes of satellites' and receivers' antenna model combinations and analyzed the results from orbit consistency and coordinates. From the result of validation, we found that compared with the use of only the CSNO-released PCOs, the orbit consistency could benefit from the estimated model of the satellite antenna phase center, particularly for BDS-2 MEO and BDS-3 SECM MEO satellites. With modeling PCCs, the 3D OBD achieves about 90.0 mm for BDS-3 MEO satellites. We also notice that the scale bias by using IGS recommended PCOs was significantly reduced when applying BDS PCC estimates. The residuals of the BDS-derived station heights are slightly reduced from 9.65 to 8.62 mm after the Helmert transformation. This demonstrates good consistency of PCO/PCC estimates in IGb14 and IGSR3 frame for BDS with other systems of GPS/GLONASS antenna offsets is achieved. Most importantly, the results demonstrate that the scale derived with BDS-released and Galileo-released PCOs is not consistent, and the bias is about +1.854 \(\pm\) 0.191 ppb. However, it must be mentioned that the estimated results of PCOs and PCVs depend on a year's data. A longer data set should be used to reduce the seasonal effects for obtaining more reliable satellite antenna models. In addition, the satellites beyond C37 should be included for further analysis. Conceptualization, J.G. and Z.Q. ; data process and analysis, Z.Q. ; writing--original draft preparation, Z.Q. ; writing--review and editing, J.G. and Z.Q. ; supervision, Q.Z. ; funding acquisition, J.G. and Q.Z. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the National Natural Science Foundation of China (grant number 41974035, 41674004), Young Elite Scientists Sponsorship Program by CAST (grant number 2018 QNIRC001). **Data Availability Statement:** Publicly available datasets were analyzed in this study. The high quality GNSS data provided by IGS and iGMAS can be found at the IGS website (ftps://gdc.cddis.eosdis.nasa.gov (accessed on 30 December 2020)) and iGMAS website, respectively. The initial combined coordinates of the third IGS reprocess available at [[ftp://igs-rf.ign.fr/pub/repro3_tests/20](ftp://igs-rf.ign.fr/pub/repro3_tests/20)]([ftp://igs-rf.ign.fr/pub/repro3_tests/20](ftp://igs-rf.ign.fr/pub/repro3_tests/20)) 08-2019/IGS1R03 TST (accessed on 30 December 2020).