SPOT vs Landsat satellite images for the evolution of the north Peloponnese coastline, Greece

The littoral zone of Achaia prefecture, located in northwestern Peloponnese of Greece, is an area which has experienced significant modification the last two decades. It is a linear and sandy coast with limited curves and infrastructures, suitable for the comparison of the shoreline derived from SPOT and Landsat satellite images. Nowadays, the application of the remote sensing has overshadowed the traditional methods of shoreline mapping, such as ground survey along with transects and airborne stereophotogrammetry, as low-cost repeatable observations can be made, providing reliable results. The normalized difference water index (NDWI), which is computed from multispectral satellite data, have been successfully applied to shoreline discrimination. Consequently, the current manuscript applies to the specific index on Landsat and SPOT data for the 1987–2008 period in order to detect the shoreline position. Moreover, shorelines were generated from the Landsat and SPOT satellite images of medium spatial resolution, 30 m and 20 m respectively, for the years of 1987, 1996, and 2008, and their accuracy was compared to respective data derived from air photos with high spatial resolution (0.50 m to 1 m). The analysis revealed that the Landsat TM 5 data provide more accurate vectorized shorelines than the SPOT 1 to 4 series with 20 m spatial resolution via the NDWI. Both are not suitable for high-scale​ accurate diachronic shoreline monitoring, even if image fusion techniques were used, as they emerged bad overlapping ratio following significant distortions on the two axes in relation to the respective high-resolution reference data. Moreover, they provided quite different results regarding the shoreline evolution in relation to the respective high-resolution data.