# Shipborne GNSS-Determined Sea Surface Heights Using Geoid Model and Realistic Dynamic Topography
## 3 Shipborne GNSS Surveys, Data, and Other Used Information  
Six marine survey campaigns were conducted in the Eastern Baltic Sea in the spring and summer of 2021 (Table 1 and Figure 2). Each campaign had a primary objective related to different Tallinn University of Technology marine condition monitoring projects. For instance, some tasks involved collecting water samples (e.g., chlorophyll, turbidity, nutrients, phytoplankton), measuring the vertical profiles of water properties (e.g., temperature, salinity, oxygen, light attenuation), or servicing marine monitoring stations. Concurrently, ellipsoidal heights were measured autonomously by four vessel-installed GNSS devices (the used instrumentation is described in [23]). The multi-frequency GNSS receivers were turned on before the vessel left the harbor, and the stored data were downloaded upon returning. During the campaigns, no dedicated GNSS operator was on-board. The GNSS sampling rates were 15 s for the first C1 campaign and 30 s for subsequent campaigns. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Campaign** \\ **Identifier** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Month** \\ **(GPS Week)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Duration of a** \\ **Campaign (h)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Route Length** \\ **of a Campaign** \\ **(km)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Number of** \\ **Grids/DT** \\ **Computation** \\ **Duration (h)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Number of** \\ **SSH Data** \\ **Points** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Temporal** \\ **Resolution of** \\ **SSH (s)** \\ \end{tabular} } \\ \hline C1 & April (2152) & 52 & 544 & 120 & 11,908 & 15 \\ C2 & July (2168) & 106 & 1439 & 168 & 12,253 & 30 \\ C3 & August (2169) & 146 & 1874 & 192 & 16,222 & 30 \\ C4 & August (2172) & 40 & 515 & 96 & 4390 & 30 \\ C5 & September (2174) & 9 & 98 & 96 & 832 & 30 \\ C6 & September (2175) & 40 & 454 & 120 & 4449 & 30 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: General information about the conducted marine survey campaigns. Figure 2: Study area (see the red rectangle) and routes of marine survey campaigns. Numbered circles denote the used TG stations, and red triangles continuously operating reference stations that were employed for GNSS post-processing. Colored background and grey isolines (contour interval is one meter) depict the NKG2015 quasigeoid model. The collected shipborne GNSS data were post-processed relative to the Estonian [34] and Latvian [35] national GNSS continuously operating reference stations (CORS) with the commercial Trimble Business Centre software (version 5.52; Trimble Inc., Sunnyvale, CA, USA). Precise GNSS ephemerides (final orbits) from the International GNSS Service were incorporated into post-processing. Since Trimble Business Centre allows only one base station at a time for kinematic data post-processing, the closest GNSS-CORS (cf. Figure 2) was always employed for a GNSS data point computation (similarly to [11; 24]). The GNSS-CORS coordinates were fixed to the reference epochs of the national reference frames (i.e., the standard data processing scheme was used). However, the Baltic Sea region's geodetic networks are deforming, primarily due to glacial isostatic adjustment induced vertical land motion (VLM). The VLM generates discrepancies between the reference and observation epoch positions of a GNSS-CORS, consequently introducing an offset to the marine GNSS measurements (cf. Figure 1), since sea level trends do not follow the VLM directly (but do contain the glacial isostatic adjustment induced geoid change). The neglected VLM correction may, thus, yield lower than actual SSH in the land uplift regions.