A Review of Tidal-Flat Remote Sensing Methods and Applications 2000–2025

Tidal-flats buffer coasts support biodiversity and are changing rapidly, yet reported global declines contrast with local expansions, leaving managers uncertain about the direction and drivers of change. Here we investigate this tension by systematically reviewing how monitoring by remote sensing has been used to observe, extract, validate, and interpret tidal-flat dynamics. We considered the literature from January 2000 to March 2025 and screened 951 records related to 339 research articles, classifying 63% (215/339) predominantly focused on tidal-flat extraction and area change, while 37% (124/339) emphasized the analysis of driving factors. Publications surged after 2019, and three tidal-flat extraction families dominate practice: waterline methods (most widely applied), image classification, and composite/optical–Synthetic Aperture Radar (SAR) fusion. Across studies, the prevailing trend is net decline in tidal-flat extent, attributed to reduced riverine sediment supply, sea level rise, and reclamation; however, robust local counter-examples exist (e.g., ~18% expansion in Germany’s Wadden Sea, 1998–2016), underscoring strong spatial heterogeneity. Although ~31% of global tidal-flats fall within protected areas, effectiveness is uneven under sustained human pressure. We synthesize common failure modes (tide/scale mismatch, validation gaps) and outline standards for multimodal data fusion and benchmarking. This review synthesizes current knowledge on tidal-flat remote sensing methods, identifies key methodological challenges, and outlines priorities for future research to support reliable monitoring.