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.