## 2 Data Collection  
In this research, two types of experiments were conducted in late 2013 [18]: Vertical Precision phase (Phase 1) and Height Modernization GPS Benchmarks (GPSBMs) phase (Phase 2). During Phase 1, the effect of different receiver/antenna combinations and the repeatability of the solutions were investigated using both static and RT solutions. Four new marks were set up in Niceville, Florida within a diamond shape, separated by about 25 m (from EAST to WEST) and 70 m (from NORTH to SOUTH). As can be seen in Figure 1, these four marks have different multipath conditions, that is, some obstructions in the north and south and a slight possibility of multipath by trees on the east. The final leveled heights are summarized for reference, which denotes the relative heights with respect to the lowest station on the east (Table 1). Figure 1: Plan view of new marks in Phase 1 [18]. The RTN involves multiple reference stations, either the CORS stations or a temporary network established for a specific purpose. The RT data can be categorized into three groups in this study: multiple-epoch single-base RT (RTK), multiple-epoch network RT (mRTN), and single-epoch network RT (sRTN). The RTN solutions were obtained by either GPS only or GNSS (GPS+GLONASS) with different occupation times, but only the GNSS case is considered in this study. For the reference coordinates of the static survey, each site was continuously occupied for 72 h (three days), followed by the antenna swap for the next session (see Table 2). Note that the same receiver/antenna combination is used for all RT solutions of Phase 1. Data collection interval is 1 Hz for both post-processing and real-time (RT) solutions. The mRTN solutions consist of a series of six positions with different durations of five, 30, 60, 180, 300, and 600 s, respectively. In Phase 2, the currently operating CORS network (approximately 35 \(\times\) 130 km), in the vicinity of Columbia, South Carolina (Figure 2), was used to investigate the effect of the baseline lengths from the same reference station as well as RT types on height information. All GPSBM stations have leveled North American Vertical Datum of 1988 (NAVD 88) orthometric heights stored in the NGS Integrated Data Base (NGSIDB). The data were also collected at a one second interval. A total of 12 permanent bases (seven NGS CORS and five base stations from South Carolina RTN) were used in the surveying (some of stations that were not directly referred to were excluded in Figure 2). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Station**} & \multicolumn{2}{c}{**Height Differences (m)**} & \multicolumn{2}{c}{**Ellipsoid Minus**} & \multicolumn{2}{c}{**Geoid Heights (m)**} \\ \cline{2-6}  & **Leveled** & **Ellipsoid** & **Leveled Ht Diff (m)** & **GEOID12A** & **USGG2012** \\ \hline NFSC-2E & 0.0000 & 0.0000 & 0.0000 & \(-\)27.348 & \(-\)28.528 \\ NFSC-2N & +0.0032 & +0.0041 & +0.0009 & \(-\)27.347 & \(-\)28.527 \\ NFSC-2S & +0.0180 & +0.0199 & +0.0019 & \(-\)27.348 & \(-\)28.528 \\ NFSC-2W & +0.4387 & +0.4407 & +0.0020 & \(-\)27.348 & \(-\)28.527 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Leveled heights of study site monuments (Phase 1) with respect to the lowest station (NFSC-2E) [18]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**EAST**} & \multicolumn{2}{c}{**NORTH**} & \multicolumn{2}{c}{**SOUTH**} & \multicolumn{2}{c}{**WEST**} & \multicolumn{1}{c}{**Note**} \\ \hline \multirow{4}{*}{Set 1} & Zephyr Geodetic & Zephyr-Model 2 & GNSS-Ti Choke & R8 GNSS/SPS88x & \\  & 2 RoHS & RoHS & SCIS & Internal & \\ \cline{2-5}  & TRM57971.00 & TRM57970.00 & TRM59900.00 & TRMR8 GNSS & \\  & NONE & NONE & SCIS & NONE & \\ \cline{2-5}  & R7 GNSS & R7 GNSS & R7 GNSS & R8 Model 3 & Receiver \\ \hline \multirow{2}{*}{Sets 2–4} & \multicolumn{4}{c}{Receiver/antenna combination moves in the following order:} \\  & & NORTH \textgreater{} EAST \textgreater{} SOUTH \textgreater{} WEST \textgreater{} NORTH & \\ \hline \hline \end{tabular}
\end{table}