Interferometric SAR and coastal vertical land motion: patterns, progress, and future priorities

Coastal vertical land motion (VLM) is a critical factor influencing relative sea-level rise, flood risk and ecosystem resilience in the most vulnerable shorelines worldwide. Here, we present the first bibliometric synthesis of 269 peer-reviewed articles published between 2002 and 2025, documenting two decades of methodological evolution in Synthetic Aperture Radar (SAR)-based VLM monitoring. Our analysis reveals a clear methodological progression, from early, localized applications of Differential InSAR (DInSAR, 11.5%) to the widespread adoption of advanced time-series techniques such as Persistent Scatterer InSAR (PSInSAR, 25.7%), Small Baseline Subset (SBAS, 20.8%) and hybrid multi-sensor approaches (22.7%) that integrate distributed scatterers and multi-frequency SAR data. Research is geographically concentrated in high-risk deltaic and urbanized coasts, particularly the Yangtze Delta (−94 to −15 mm/yr), Yellow River Delta (−271 to −5.1 mm/yr), Mekong Delta (−50 to −5 mm/yr), Shanghai (−14 to −2.1 mm/yr) and Jakarta (−250 to −100 mm/yr), where subsidence rates frequently exceed global sea-level rise by an order of magnitude. Increasing integration of SAR with Global Navigation Satellite System (GNSS), Light Detection and Ranging (LiDAR), tide gauges and hydrological data has significantly improved deformation attribution to natural and anthropogenic drivers, including groundwater withdrawal, land reclamation and infrastructure loading. By synthesizing methodological trends, geographic patterns and emerging research priorities, we highlight both substantial progress and persistent gaps, particularly in Africa, small island states and vegetated coastal systems, and outline key pathways to advance operational, multi-sensor VLM monitoring for coastal risk assessment.