Monitoring coastal shoreline change using PlanetScope imagery

Accurate monitoring of shoreline change is essential for assessing coastal vulnerability, yet traditional field surveys and airborne mapping are costly, logistically demanding, and spatially limited. Here, we present an automated workflow that leverages high-spatial-resolution (≈3 m), near-daily PlanetScope imagery to detect multi-year shoreline change across diverse coastlines. Rather than extracting instantaneous shoreline positions, the method exploits dense, multi-year time series of the Normalized Difference Water Index (NDWI) to quantify pixel-based temporal trends, which are extrapolated to consistent start ( T 0 ) and end dates ( T f ). This approach yields extrapolated shoreline positions at T 0 and T f that represent long-term erosion and deposition patterns while suppressing the influence of short-term and seasonal water-level variability, episodic events, and optical noise. The workflow was developed and tested across twelve U.S. National Park Service coastal sites, eight of which include field-surveyed reference shorelines. Remotely sensed shoreline-change maps for the 2017-2021 time period showed strong spatial agreement with survey-derived erosion and deposition patterns, and estimated change areas were within ±20% of field benchmarks despite inherent temporal differences between instantaneous surveys and extrapolated shoreline positions. Application at four additional sites lacking field surveys demonstrated broad geographic robustness while revealing limitations in settings characterized by subtle lateral changes or periodically inundated vegetation. The workflow is computationally efficient, scalable, and well-suited for reconnaissance-level assessments to inform coastal management and prioritize field efforts. Although it is not designed to resolve short-term shoreline morphodynamics, it provides a practical framework to identify multi-year erosion and deposition patterns from 2017 onward across diverse coastlines. • Rapid shoreline-change detection using PlanetScope imagery • Remotely sensed multi-year shoreline change is consistent with field surveys • Approach enables automated shoreline assessments to identify vulnerable areas • Broad applicability across diverse coastal shorelines