Subpixel Satellite-Derived Shorelines As Valuable Data for Equilibrium Shoreline Evolution Models

The analysis and prediction of shoreline variability are two of the main challenges in coastal engineering. Evaluating coastal behaviour in a target area usually requires access to long data series of high-resolution shoreline positions. Therefore, coastal engineers must have access to different data sources, such as topographic-bathymetric field campaigns, digital orthophotos, aerial photographs, video-camera monitoring systems, and satellite imagery. This last data source is the only one that has the great advantage of covering large areas of the world and including regular coverage of most coasts during all climates and seasons. However, mid-resolution satellite images have been neglected because the resolution available to the public is too coarse to provide information on most coastal morphodynamic changes. The aim of this study was to explore the applicability of mid-resolution satellite imagery with a subpixel acquisition method for the calibration and validation of equilibrium shoreline evolution models. The models' performance was assessed by means of a comparative analysis between shoreline-position data sets obtained from video-camera systems and satellite imagery at two beaches on the Mediterranean coast of Spain. Almost 4 months of shoreline measurements were considered for validation purposes of the models at Nova Icaria Beach, and more than 1.5 years of shoreline measurements were analyzed at Cala Millor Beach. The results show that the general erosion-accretion trend is adequately represented by the models compared to the shoreline measurements at a qualitative and quantitative level.