Multi-site assessment of microtidal wave-dominated active beach state and morpho-sedimentary parameters using optical satellite imagery

Traditionally, beach states are defined from visual observations, in-situ measurements and/or video imagery, which limits their application to a handful of well-instrumented sites. In this work, we propose a different approach by focusing on a remotely observable quantity: the cross-shore distance between the offshore wave-breaking and the shoreline position, denoted [Formula: see text]. This metric defines the active beach state, capturing where waves dissipate energy relative to the underlying morphology. Using 10 years of Sentinel-2 imagery, [Formula: see text] is evaluated across 30 wave-dominated microtidal sandy beaches spanning reflective to fully dissipative conditions. The metric reproduces the structure of classical beach state frameworks and enables classification into five active states (R, LTT, TBR/RBB, LBT, and D) using transferable thresholds. [Formula: see text] is continuous, thus it also reveals how beach state evolve through time, allowing quantification of state occurrence, residence time, and transitions, with seasonal variability consistent with independent classifications at well-studied sites. Furthermore, using empirical relationships, we demonstrate that [Formula: see text] carries first-order information about beach-face slope ([Formula: see text]) and sediment grain size ([Formula: see text]), opening a pathway toward systematic satellite-based monitoring of coastal morphodynamics at regional to global scales.