12 Aug 2025

Assessing Shorelines Extracted from Satellite Imagery Using Coincident Terrestrial Lidar Linescans

Abstract: Previous analyses comparing CoastSat satellite-derived shorelines to morphological data highlighted site-specific errors in outputs related to concurrent wave runup conditions. We present a comparison of lidar-derived runup and beach elevation data to CoastSat satellite-derived waterlines extracted using two image sources and two threshold algorithms. Results show SDW extracted using Otsu thresholds correlated better with lidar-derived waterlines, SDW extracted using the weighted peaks threshold were consistently positioned in the upper swash and correlated better with a runup bulk statistic. Assigning the best-fit runup bulk statistic as the waterline elevation to weighted peaks SDW resulted in SDS with less scatter than the Otsu SDW. Horizontal errors for converted datum-referenced shoreline were lowest when SDW were converted to SDS using best-fit measured runup bulk statistics and a measured slope. For weighted peaks SDW from both image sources, assigning the best-fit parameterized runup bulk statistic and an average slope in the SDW to SDS conversion reduced error by ∼ 20% to ∼ 35% when compared to tidal elevation and average slope. These findings confirm runup corrections can improve native SDS outputs, although the magnitude of final shorelines error depended on specific imagery product, local beach slope, threshold technique, runup parametrization, and chosen reference contour.

13 Jun 2024

Quantifying Coastal Evolution and Project Performance at Beaches by Using Satellite Imagery

Abstract: Accurately delineating the shoreline is crucial for tracking coastal evolution, community vulnerability, storm impacts, and for coastal management decision-making. However, existing shoreline measurement methods are often time-consuming and expensive and therefore, USACE Districts are often forced to narrow areas of interest or monitoring frequency, decreasing the likelihood of making data-driven management decisions, especially over regional scales. In the last decade, space-borne earth observations have captured images subweekly, and can potentially be used for shoreline monitoring. This work investigated the Python-based CoastSat toolkit and compared the shorelines derived from publicly available satellite imagery to ground truth surveys at 37 sites across the nation chosen in coordination with Districts. Mean horizontal errors ranged from 4.21 to 20.58 m with an overall mean of 11.32 m. Tidal corrections improved accuracies at 82% of sites. The CoastSat slope function was tested and there were negligible differences in shoreline accuracy when compared with user-defined slopes Twenty-year satellite-derived trends generally align well with ground truth trends. The satellite approach identified quantifying storm impacts/recovery, beach nourishment equilibration, diffusion and decay, shoreline response to nearshore berm placements and decadal shoreline evolution at the evaluated district sites. Work is ongoing to transition to a user-friendly software tool.