Using GIS tools to enhance the shape of coastline extracted from Sentinel-2 satellite images

Sentinel-2 images are widely used for coastline extraction. One of the most widespread methods is the Normalized Difference Water Index (NDWI), which permits distinguishing between water and non-water pixels. The result obtained, since it derives from satellite images, preserves the shape of the pixels, which is often labeled as unrealistic. For this reason, Geographic Information Systems (GIS) tools are often used in the literature to simplify and/or smooth the coastline obtained from satellite images in order to make it as similar to reality as possible. However, these operations are not always optimal. In this work, we analyze the coastline extracted from Sentinel-2 images concerning the island of Giglio (Italy), in particular four coastlines are compared: the standard coastline, i.e. the one obtained directly from the NDWI; the coastline resulting from the smoothing application; the coastline resulting from the simplification application; and finally, the coastline resulting from both simplification and smoothing application. The results show a higher efficiency of smoothing compared to simplification.