A review on the use of Synthetic Aperture Radar (SAR) for monitoring shorelines and intertidal areas

Effective monitoring of morphological changes in coasts is essential for understanding multiscale evolution, managing hazards and supporting sustainable development. Optical satellite imagery has long supported coastal monitoring, but its dependence on daylight and cloud-free conditions limits temporal and spatial coverage. Synthetic Aperture Radar (SAR) overcomes many of these constraints through all-weather, day–night acquisitions and sensitivity to surface roughness, moisture and dielectric properties, making it a promising yet still underexploited resource for coastal monitoring. Given this potential, and the still limited understanding of SAR applications for coastal morphology monitoring, this paper presents a review on the current knowledge on SAR-based morphology mapping, focusing on shoreline detection and intertidal topography retrieval. We examine the main preprocessing and extraction methodologies, including speckle filtering, segmentation, shoreline extraction and post-processing, and discuss different approaches for intertidal topography mapping across diverse coastal environments. The influence of sensor configuration, including frequency band, polarization and acquisition geometry, is reviewed alongside the role of environmental and morphodynamic conditions in shaping detection performance. Key sources of uncertainty are highlighted, emphasizing the scarcity of reliable and harmonized ground truth data, which continues to constrain validation and cross-parameter and cross-site comparisons. The review identifies recurring patterns, limitations and challenges that currently hinder broader operational use of SAR shoreline and intertidal topography mapping. Based on this synthesis, priority directions for future research are identified, including more systematic experiments across contrasting morphodynamic settings, improved reference datasets, higher levels of automation and closer integration with complementary data sources, to better exploit SAR for large-scale and long-term coastal monitoring and hazard assessment.