Shoreline change assessment at Arroio do Sal (Southern Brazil) using different shoreline extraction methods

Abstract

This research aims to compare different shoreline extraction methods in assessing shoreline variability at Arroio do Sal, Southern Brazil. The methodology included the automatic extraction of shoreline positions by CoastSat and Cassie and the manual vectorization of shorelines using two different shoreline proxies. Digital Shoreline Analysis System was used to compute the shoreline displacement for each extraction method and shoreline mission. The results were compared in terms of rates, uncertainties, and methodologies. The results show that the CoastSat lines are generally displaced towards the land, while Cassie is displaced towards the sea. To concerning shape, Cassie has a more undulating shape and a greater number of indentations, with more exaggerated features, while CoastSat has a more rectilinear line, with smoother indentations next to the washouts. The RMSE values are 8.89 m for CoastSat and 27.27 m for Cassie. Despite the variations in the coastline position between the algorithms, the analyses of the rates of change have similar trends. Both algorithms establish an erosion trend for the Sentinel lines, but with different magnitudes; for the Landsat lines, both algorithms show a stable coastline, with the same average and uncertainty. Arroio do Sal can be considered a stable coastline, with rates of change in the −0.5 m–0.5 m range. Both algorithms were able to determine this general trend.