## 4 Data Collection and Result Discussion
### Repeatability Accuracy Validation  
The repeatability accuracy can validate the stability and reliability of the calibrated antenna PCO and PCV values. We computed individual calibrations for the same antenna type TRM57971.00/NONE but from different days in 2014. The calibration results displayed in Table 1 show that there exist some slight discrepancies from each session, described by the standard deviations about 0.17 mm, 0.12 and 0.30 mm in the north-east-up components. Also the estimated PCOs apparently differ from each other in three components. The horizontal components (north and east) with sub-millimeter range, but the vertical component come up to almost 70 mm, which should not be neglected in high-precise positioning applications. Additionally, the elevation only and full PCVs (elevation and azimuth dependent) are also estimated for the test antenna (TRM57971.00/NONE), which are shown below Figure 6. Figure 6 demonstrates the agreements between five calibrated results and their discrepancies with IGS type values for the tested antenna. For the repeatability, some small gaps of \(\pm\)0.5 mm can be observed in the zenith range of 0-80\({}^{\circ}\) calibrated on different days (gray line DAY240-2014 and green line DAY297-2014). These gaps increased at low elevation signal reception orientations, and an inconsistency of nearly 1 mm may be partly found (see Figure 6). The bad receiving behavior for most antennas at low elevations can be responsible for this [8], and this is true for full PCV estimation (see Figure 7). Furthermore, we expanded several additional calibrations to examine the performance of our calibrating procedure implemented in this paper. As shown in Table 1, both the test geodetic antennas TRM59800.00/NONE and LEIAR25/NONE show good repeatability accuracy. The standard deviations for the north, east and up components are better than 0.5 mm.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Day of Year 2014** & **Antenna Type** & **North (mm)** & **East (mm)** & **Up (mm)** & **Standard Deviation (mm)** \\ \hline
**026** & & 0.92 & \(-\)0.10 & 66.92 & \\
**064** & & 0.97 & \(-\)0.25 & 67.01 & \\
**112** & TRM57971.00/NONE & 1.33 & \(-\)0.38 & 66.68 & \(\sigma_{N}=0.17\), \(\sigma_{E}=0.12\), \(\sigma_{U}=0.30\) \\
**240** & & 1.24 & \(-\)0.35 & 66.99 & \\
**297** & & 1.09 & \(-\)0.34 & 67.50 & \\ \hline
**026** & & 0.55 & 1.14 & 90.02 & \\
**241** & & 0.61 & 1.49 & 89.66 & \\ \hline
**065** & & 1.33 & 0.78 & 155.77 & \\
**113** & LEIAR25/NONE & 1.28 & 0.92 & 155.53 & \\ \hline \hline \end{tabular}
\end{table}
Table 1: PCO solutions for all sessions and the corresponding standard deviations.  
Figure 6: Zenith or elevation-only dependent PCVs of GPS L1 frequency, for the Trimble Zephyr Geodetic antenna TRM57971.00/NONE. The five days of independent calibrated results are in good accord with the IGS type for this antenna.  
Figure 7: Differences of two independent calibration (DAY240 _vs._ DAY297-2014) derived full PCVs of GPS L1 frequency (TRM57971.00). For the repeatability, some small gaps within 1 mm can be found in the mostly zenith range of 0–80\({}^{\circ}\). Some parts of 2–4 mm discrepancies arose near the horizon of the antenna pan.