# Phase Centre Corrections of GNSS Antennas and Their Consistency with ATX Catalogues
## 4 Results  
The difference in heights between KRAW, KRA1, KR01, and KR02 was calculated by post-processing of the observations. Due to the KRAW Ashtech UZ-12 receiver capability, only the GPS system was used. Post-processing was based on the final IGS orbits, the igs08.4 tx antenna corrections model, and a zero-elevation mask. Height differences obtained from precise levelling were compared with those derived from EPN-combined solutions, PPP calculated with Bernese GNSS Software (BGS) [30], Nevada Geodetic Laboratory (NGL, [31]), a network solution, a single baseline solution (GNSS Solutions 3.80.8, Trimble Business Centre 3.50), and other archive materials. In GNSS Solutions, only the elevation-dependent PCV version of the antenna characteristics was used. Height differences obtained from precise levelling and GNSS solutions showed several discrepancies. Height differences between the KRA1 antenna reference point and the three other measured stations (KRAW, KR01, and KR02) from GNSS post-processing are affected by the inaccuracy of the antenna PCO and PCV. The analysis shows that the height of the KRAW station antenna (ASH70195C_M SNOW) from GNSS processing (EPN combined and PPP solutions) is 16 mm too high in comparison to the levelling results (Figure 6). This may indicate the inadequacy of the ASH70195C_M SNOW calibration data. A lower disagreement was obtained in the case of the TRM57971.00 NONE antenna (KR01 and KR02 stations). This discrepancy was about 5 mm for PPP solutions and 2 mm for network solutions. The differences obtained by single baseline solutions using the Trimble Business Centre (TBC) and GNSS Solution engineering software show far fewer discrepancies, not exceeding 0.4 mm. This is due to the very short baseline between the measured points. The height difference of KRAW-KRA1 was calculated based on the EPN weekly combined SINEX (Software INdependent Exchange format) solutions from 2010 to 2016 (1564 to 1877 GPS weeks, Figure 7). During weeks when igs08 and igb08 were in use, there were some inaccurate solutions, which may be treated as gross errors. Despite that, clearly visible is the change in ellipsoidal height difference after the introduction of the IGS14 system (after GPS week 1933 [33]). The offset is up to about 8 mm (Figure 7). It is surprising that, during the short time between the introduction of the IGS14 system and individual phase corrections for the KRA1 antenna (week 1986), the height difference was closest to levelling (\(-0.5\) mm) from any network calculation. Figure 6: Differences between the heights obtained with PPP and a network solution (**left**) and single baseline solutions (**right**) [32]. Alternatively, an independent PPP calculation was used--the Nevada Geodetic Laboratory (NGL). The facility provides permanent, fully, and freely available PPP results based on globally distributed permanent GNSS station data. Based on these data, the ellipsoidal height differences between station KRAW and KRA1 for the period 2009.7-2022.0 GPS weeks 1569-2190) were analysed (Figure 8). The results showed a mean difference +1.83 mm (green line) and were compared to precise geometric levelling \(-6.2\) mm (red line). Both data provided inaccurate results, which was not a surprise, as they were based on the different antenna characteristics (IGS Antex files) of the KRAW antenna. The archival materials regarding the height differences between the KRAW-KRA1 stations consist of: two independent sets of post-processing results from 2008 to 2011 calculated during the Polish integration of the base geodetic network with reference permanent  
Figure 8: Height difference between KRA1–KRAW from NGL–PPP (navy dots), systematic difference from levelling \(-6.2\) mm (red line), and mean difference 1.83 mm (green line) [31]. Figure 7: The time series for the height difference between KRAW–KRA1 calculated by EPN on the basis of several antenna correction catalogues (IGS ATX files) [32].