Satellite-derived shorelines for monitoring of sandy beaches: a benchmark study

Kilian Vos , Kristen D Splinter , Jesús Palomar-Vázquez, Josep Eliseu Pardo-Pascual, Carlos Cabezas-Rabadán, Jaime Almonacid-Caballer, Etienne Kras, Arjen Luijendijk, Floris Calkoen, Luis Pedro Almeida, Daniel Pais, Antonio Henrique Klein, Yongjing Mao, Daniel Harris, Bruno Castelle, Daniel Buscombe, Sean Vitousek

Satellite remote sensing is becoming a widely used monitoring technique in coastal sciences. Yet, no benchmarking studies exist that compare the performance of popular satellite-derived shoreline (SDS) mapping algorithms against standardized sets of inputs and validation data. Here we present a new benchmarking framework to evaluate the accuracy of shoreline change observations extracted from publicly available satellite imagery (Landsat and Sentinel-2). Accuracy and precision of five established SDS algorithms are evaluated at four sandy beaches with varying geologic and oceanographic conditions. Comparisons against long-term in situ beach surveys reveal that all algorithms provide horizontal accuracy on the order of 10 m at microtidal sites. However, accuracy deteriorates as the tidal range increases, to more than 20 m for a high-energy macrotidal beach (Truc Vert, France) with complex foreshore morphology. The goal of this open-source, collaborative benchmarking framework is to identify areas of improvement for SDS algorithms, while providing a stepping stone for testing future developments, and ensuring reproducibility of methods across various research groups and applications.