# Space-Based Displacement Monitoring of Coastal Urban Areas: The Case of Limassol's Coastal Front
## 2 Materials and Methods
### Data Processing
#### 2.2.3 Leveling Equipment and Measurements  
As a ground-based geodetic technique, precise leveling was selected for its simplicity and unmatched accuracy [53]. In total, thirteen (13) benchmarks across the coastline of Limassol were remeasured [Figure 6, Table 4]. The CUT Laboratory of Geodesy established a vertical control network that covers the broader Limassol area in late 2016. Since then, yearly geodetic leveling surveys have been carried out to monitor the vertical component variability. The leveling network was tied to the CUT Tide Gauge station in Limassol, which is a part of the National Geodetic Infrastructure and, therefore, tied to the national vertical datum of Cyprus. For the specific study, the leveling benchmark CUT2 was considered as our control benchmark [Figure 7]. The height difference between epochs 2017 and 2021 was used as a reference for the validation of PSI results at Limassol coastal front.  
Figure 5: Mean velocity of persistent scatterers at the area of study (Limassol coastal front).  
Figure 6: Locations of leveling benchmarks on Limassol coastal front. The yellow circle defines the control benchmark (CUT2), while yellow triangles show the measured benchmarks. All heights were obtained from the national vertical datum of Cyprus.  
In the current study, the height differences were acquired by leveling surveys using the high-precision digital Leica LS15 and two fiberglass staffs (GTM4L). The calculation of the orthometric height was computed in Leica Infinity software. The measurements were provided with a fiberglass bar code that allowed a resolution of 0.1 mm in electronic height measurements, offering a height accuracy of \(\pm\)1.0 mm per 1 km for double-run measurements (ISO 17123-2). The procedures conducted before (instrument alignment), during (alternating back and forward sightings), and after (the orthometric correction) the measurements eliminated the main sources of errors such as rod alignment, the curvature  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Leveling Benchmark** & **Orthometric Height** & **Orthometric Height** & **Height Differences** \\
**ID** & **2017 (m)** & **2021 (m)** & **2017–2021 (m)** \\ \hline \hline LVD048 & 3.401 & 3.402 & 0.001 \\ \hline LVD047 & 3.618 & 3.619 & 0.001 \\ \hline LVD034 & 2.181 & 2.174 & \(-\)0.007 \\ \hline LVD046 & 3.530 & 3.532 & 0.002 \\ \hline LVD045 & 5.399 & 5.401 & 0.002 \\ \hline LVD033 & 3.591 & 3.593 & 0.002 \\ \hline LVD044 & 3.429 & 3.433 & 0.004 \\ \hline LVD032 & 3.471 & 3.473 & 0.002 \\ \hline LVD043 & 2.581 & 2.583 & 0.002 \\ \hline LVD031 & 2.696 & 2.700 & 0.004 \\ \hline LVD042 & 2.559 & 2.583 & 0.024 \\ \hline LVD030 & 2.442 & 2.443 & 0.001 \\ \hline LVD041 & 1.805 & 1.807 & 0.002 \\ \hline
**CUT2**\({}^{\dagger}\) & 1.877 & 1.877 & 0.000 \\ \hline \hline \end{tabular} \({}^{\dagger}\) CUT2 is the control benchmark.  
\end{table}
Table 4: Features (ID, height) of thirteen (13) leveling benchmarks in 2017–2021.  
Figure 7: (**a**) CUT2 control leveling benchmark and (**b**) checkpoint leveling benchmarks installed by the CUT Laboratory of Geodesy in 2016.  
and refraction errors, and other several systematic errors. The tolerance error for the first-order class II survey of a section of 2 km (maximum) line length is 4 mm \(\surd\)K and 5 mm \(\surd\)K for an entire leveling line, where K is the length of the leveling line, measured in kilometer units [54]. It should be noted that the heights of leveling benchmarks were referenced to the Cyprus Vertical Datum.