## 4 Advancements in Remote Sensing Technologies for Coastal Monitoring
### Satellite Data for Coastal Monitoring  
Both the Sentinel and Landsat missions serve complementary functions in shoreline surveillance, each superior in different temporal and spatial regimes. Sentinel-2 has high resolution (10 m) and 5-day revisits, making it very effective for detecting relatively short-term shoreline changes related to storms, tidal action, or human activities, with near-real-time coastal hazard information [47]. Its shorter temporal record since 2015, however, hinders it in the analysis of long-term trends. On the other hand, Landsat satellites provide a four-decade record of observation beginning in 1972, which is extremely useful for the analysis of long-term coastal trends like gradual sea level rise or sediment re-allocation [20, 51]. Though its 30 m spatial resolution and recurring 16-day visitation may overlook finer-scale events, Landsat is an anchor resource for historical shoreline analysis [19]. Furthermore, the Synthetic Aperture Radar (SAR) mission, Sentinel-1, provides monitoring in environments where optical sensors are inadequate such as under cloud cover, during night-time imaging, or in sediment-charged waters [55, 69]. SAR can monitor changes in surface roughness, suitable for identifying land-water interfaces even in adverse environments [81]. Though it has poorer spatial resolution and less ability to discriminate close surfaces such as wet sand and shallow water, Sentinel-1 is especially useful in monsoon-hit or tropical environments [82, 83]. Studies like those of [PERSON] et al. (2021), [PERSON] et al. (2021), and [PERSON] et al. (2023) [35, 39, 55] indicate the efficiency of Sentinel-1 SAR, either used individually or combined with optical data, in providing improved accuracy in shoreline mapping. These studies verify the efficacy of the combination of SAR and optical data in compensating for inherent weaknesses in either dataset to provide consistent monitoring regardless of different environmental scenarios. Table 4 compared major studies using Sentinel-1 SAR for shoreline detection and change detection based on the review content of the selected studies. \begin{table}
\begin{tabular}{p{42.7 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Reference** & \
\begin{tabular}{c} **Geographical** \\ **and Temporal** \\ **Scope** \\ \end{tabular} & **Sentinel-1** & **Satellite Data** &
\begin{tabular}{c} **Sh shoreline** \\ **Change** \\ **Metrics** \\ \end{tabular} & **Key Findings** & **Unique Features** \\ \hline
[35] & East Java Province, Indonesia (2000–2019) & Used for shoreline monitoring & Landsat-7, ALOS Pulsar, Sentinel-1 & \
\begin{tabular}{c} Landsat-7, \\ Landsat-8, \\ ALOS Pulsar, \\ Sentinel-1 \\ \end{tabular} & EPR, WLR &
\begin{tabular}{c} Coastal accretion \\ was more \\ significant than \\ erosion, with an \\ average accretion \\ of +4.12 m/year \\ \end{tabular} & Multi-sensor approach using random forest and \\
[35] & East Java Province, Indonesia (2000–2019) & Used for shoreline monitoring & Landsat-8, ALOS Pulsar, Sentinel-1 & \begin{tabular}{c} EPS, WLR \\ Aerospace \\ of +4.12 m/year \\ \end{tabular} & EPR, WLR & \
\begin{tabular}{c} Regional direction, with an \\ average accretion \\ of +4.12 m/year \\ \end{tabular} &
\begin{tabular}{c} Google Earth Engine \\ for improved \\ shoreline mapping \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Sentinel-1 SAR data for enhanced shoreline detection, providing insights into the key findings of each research and unique features. Sentinel-Landsat Synergy in Shoreline Monitoring  
A synergistic combination of both missions, for the monitoring of short-term processes with Sentinel and long-term trends with Landsat, presents the most authoritative coverage for coastal research. The fusion of Sentinel-2 and Landsat imagery has emerged as a powerful strategy for monitoring coastal dynamics by combining the high spatial and temporal resolution of Sentinel-2 with the long historical archive of Landsat, as our review identified in the selected studies [43; 47; 69; 84].