## 3 Calibration Methodology  
The goal of our calibration is to estimate elevation-averaged PCVs in ANTEX format for the investigated rover antennas using the residuals obtained using a short baseline. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Type** & **Receiver** & **Antenna** \\ \hline base & Trimble NetR9 & Leica AR25.R3 LEIT (LEIAR) \\ \hline  & & u-blox ANN-MB-00 (ANN-MB) using rectangular adaptor bracket (r) \\  & & u-blox ANN-MB-00 (ANN-MB) using circular plane (c) \\  & & Trimble AV28 (AV28) using rectangular adaptor bracket (r) \\ rover & u-blox ZED-F9P & Trimble AV28 (AV28) using circular plane (c) \\  & & Trimble GA530 (GA530) \\  & & Trimble TRM55971.00 NONE, Zephyr 2 geodetic (TRM5) \\  & & Leica AR25.R3 LEIT (LEIAR) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Utilized base and rover receiver and antennas at the experimental site. The obtained PCVs can be applied to the rover carrier phase observations to improve the residuals (see Section 4) and positioning results (see Section 6). With our method, which is a relative antenna calibration, site-dependent factors that are different between base and rover antenna will affect the estimated residuals and will therefore directly influence the estimated PCVs. The site-dependent factors (multipath) are unique for each installation and will influence the estimated parameters. They cannot be covered fully in antenna calibrations except if the calibration is performed in the same spot as the experimental location. Three scenarios are possible: (i) bring the rover to the base (calibration site) for calibration, (ii) bring the base (with geodetic grade calibrated antenna) to the rover (in-situ) for calibration, or (iii) do an in-situ calibration. Only when the calibration is done completely in situ (i.e., the same base is used for calibration and the experiment) site-dependent effects will be mitigated. However, this requires the rover and/or base not to change after the calibration is done. This means processing relatively long baselines during the calibration phase, possibly taking multiple days. Another interesting option is to use Virtual Reference Station (VRS) data. These could be utilized in zero-baseline mode. The second-best option is number (ii), where the base station is temporarily brought to the experiment site. This is inverting scenario (i). It also assumes that the local site effects are smaller when the calibrated geodetic antenna is brought to the rover, instead of bringing the rover to a calibration site (option i). The words \"antenna calibration\" can be slightly misleading in this context: we have in mind to calibrate low-cost antennas in their final settings as much as possible, including local site effects, and not per se only the antenna itself. Apart from the residuals, only the time-independent static baseline vector, time-dependent clock, and carrier phase ambiguity parameters are estimated in the calibration step. The data processing is primarily realized using the open-source tool RTKLIB [14]. The applied processing options can be found in Table 1 in the Appendix A. One result of the RTKLIB process is Double Differenced (DD) carrier phase residuals for each frequency and each common satellite with a resolution of 0.1\({}^{\circ}\) in elevation and azimuth. To obtain Single Differenced (SD) residuals, which are required to analyze the PCVs, the RTKLIB source code is modified to subtract the average of the DD residuals from the DD residuals. See also Github issue: [[https://github.com/tomojitakasu/RTKLIB/issues/457](https://github.com/tomojitakasu/RTKLIB/issues/457)]([https://github.com/tomojitakasu/RTKLIB/issues/457](https://github.com/tomojitakasu/RTKLIB/issues/457)) (accessed on 9 February 2022). It avoids calculating the SDs from the DDs manually.