## 3 Results
### Start Bay  
Figure 11 in Appendix A shows the location of all the SLs derived from ASC (701 lines) and DESC (701 lines) orbits at the Start Bay study site between the years 2015 and 2021. The RL used is the same datum-based tideline used by [15], which represents the contour at \(-1.3\) m elevation relative to the ordnance datum extracted from the 2019 SurfZone DEM. SAR-SLs seem able to delineate the relatively homogeneous and rectilinear gravel beach, the very irregular rocky outcrops, and the large lagoon. A visual inspection of SAR-SLs indicates that they are predominately continuous with few spurious lines. In places, the SL appears as spurious irregular segments, with this being most appreciable for ASC SLs at the northern and southern ends of the large embayment and for the DESC SLs at the seaside and center of the large embayment. A zoomed-in view of different regions showing all lines (ASC and DESC SLs) in bulk reveals that there is not a clear tendency of lines extracted from one orbit to appear systematically landward or seaward with respect to the other. A zoomed-in inspection of individual SLs reveals that the SLs are wiggly at places, but this did not appear to be too detrimental to the understanding of the line as a water-land approximate interface. The width of the envelope of all SLs in the enclosed lagoon area is of the order of 30 m and appreciable smaller than along the open coast, where it is of the order of 150 m. We noticed that only a subset, six and eleven SLs for ASC and DESC, respectively, of the seven-hundred and one SLs mapped the lagoon as part of the open coast, suggesting that the barrier might have been breached. The dates on which the lagoon was mapped for the ASC SLs are all different from those the DESC SLs (see Table 7). \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{**SL Collection Date, Time, and Astronomical Tidal Level**} \\ \cline{2-3}
**DTM Collection Date** & **Assending SLs** & **Descending SLs** \\ \hline
10 March 2016 & 11 March 2016 18:05:17 \(\uparrow\) 1.1 m & 08 March 2016 06:31:08 \(\uparrow\) 1.5 m \\
12 September 2018 & 10 September 2018 17:56:36 \(\uparrow\) 2.4 m & \(\uparrow\) 12 September 2018 06:31:08 \(\uparrow\) 1.7 m \\
19 September 2020 & 17 September 2020 17:57:42 \(\uparrow\) 2.7 m & \(\uparrow\) 19 September 2020 06:31:50 \(\uparrow\) 2.2 m \\ \hline \hline \end{tabular} \(\ddagger\) Collection dates of DTMs and SLs within less than 24 h difference; \(\uparrow\) ascending tide; \(\downarrow\) descending tide; \(\uparrow\)\(\downarrow\) high tide.  
\end{table} 
Table 7: Dates of DTM collection, and dates and time of ASC and DESC SLs used for the analysis. It is also indicated if the astronomical tide was ascending, descending, or at high tide at the time of satellite data collection. Figure 16: Measured beach profile (No. 6) and CoastSat WL distance from the baseline in Salinas beach (top panel a); heatmaps of concentration of CoastSat WLs across the beach profile (bottom panel a). Measured beach profile (No. 6) and CoastSat SL distance from the baseline in Salinas beach (top panel b); heatmaps of concentration of CoastSat SLs across the beach profile (bottom panel b). Figure 17 shows the summary statistics of the astronomical daily high and low tide elevation at Start Bay between the years 2015 and 2021, together with the elevation at the time when the satellite data were collected grouped into ASC and DESC tracks. All tide elevations are shown relative to Ordnance Datum Newlyn (ODN). The passing times are between 17:57 and 18:05 UTC (coordinated universal time) for the ASC tracks and between 6:23 and 6:31 UTC for the DESC tracks.