# Preliminary Results of an Astri/UWM EGNSS Receiver Antenna Calibration Facility
## 7 Elevation-Only PCC Validation  
PCCs are a function of the PCO and PCVs and can be expressed as elevation-only dependent or elevation- and azimuth-dependent functions (full PCCs). The first solution (elevation-only model) is usually used in so called \"commercial software\", where the highest accuracy and precision of results is not required, and also in kinematic applications, where the horizontal orientation of a rover antenna cannot typically be measured.  
In this section, we analyze elevation-only dependent PCCs models obtained during Astri/UWM calibrations. At the first stage, both compared sets of results have to be shifted to PCV(\(\alpha\),0) = 0 (zenith PCV = 0) in case this was not done during the calibration process. This shift can be done by adding constant value \(\delta=-PCV(\alpha,0)\) to all derived PCVs. After adding \(\delta\), the PCO vertical component should also be corrected. The corrected PCO vertical component can be described in the form of \(PCOup^{corr}=PCOup-\delta\). In the final step, we can compare two models by reducing the PCCs of the first one (compared) to the PCO of the second one (reference) using a general formula [30]:  
\[PCC(\alpha,z)=s^{T}PCO_{r}+\left(PCV_{c}(\alpha,z)+s^{T}(PCO_{c}-PCO_{r})\right) \tag{6}\]  
where PCC denotes the compared PCC after reduction to reference PCO, PCO\({}_{r}\) is the PCO of the reference model, PCV\({}_{c}\) denotes the PCV of the compared model and PCO\({}_{c}\) is the PCO of compared model. The resulting reference and compared PCVs can be analyzed by forming difference patterns (dPCCs). Figure 7 demonstrates the consistency between the calibrated results and their discrepancies with IGS-type (mean) values for both tested antennas.  
It can be concluded from the analysis of the internal accuracy of the achieved results (PCCs model repeatability) that we have obtained consistent results. The differences do not exceed 1.5 mm in the whole estimated zenith angle range (from 0\({}^{\circ}\) to 90\({}^{\circ}\)) for both tested antennas. When we compare the Astri/UWM results with the reference model (igs14.atx), the differences increase slightly (e.g., calibration 3 for TRM115000.00/NONE antenna), exceeding 1 mm for the zenith angle regions.  
The most significant differences occur at low zenith angles (from 0\({}^{\circ}\) to 30\({}^{\circ}\)), which is mainly caused by the differences in PCO vertical components. Some increases in differences can be also observed for very high zenith angles (from 80\({}^{\circ}\) to 90\({}^{\circ}\)), which can also be observed for full PCC comparison (see Figures 7 and 8). In this case, the reason is higher noise in observations, which is common for high zenith angle signals [31].  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Calibration No**} & \multirow{2}{*}{**Antenna Type**} & \multicolumn{3}{c}{**PCO (mm)**} & \multicolumn{3}{c}{**PCO SD (mm)**} \\ \cline{3-8}  & & **North** & **East** & **Up** & **North** & **East** & **Up** \\ \hline
1 & & +1.31 & \(-\)0.52 & +86.26 & & & \\
2 & & +1.12 & \(-\)0.68 & +87.33 & 0.19 & 0.25 & 0.56 \\
3 & LEIAR10 NONE & & +0.85 & \(-\)0.09 & +86.05 & & & \\ \hline igs14.atx & & +1.42 & \(-\)0.25 & +88.04 & - & - & - \\ \hline
1 & & +1.03 & +0.27 & +64.75 & & & \\
2 & & +0.75 & +0.36 & +64.05 & 0.26 & 0.22 & 0.52 \\
3 & TRM115000.00 NONE & & +0.38 & +0.77 & +63.49 & & & \\ \hline igs14.atx & & +0.68 & \(-\)0.12 & +65.19 & - & - & - \\ \hline \hline \end{tabular}
\end{table}
Table 2: PCO test solutions for all sessions and the corresponding standard deviations.