4D Point Cloud Analysis of the September 2020 Medicane Impact on Myrtos Beach in Cephalonia, Greece

Abstract

[EN] The coastal area of Myrtos beach, is a very popular Natura protected area at the Northern part of Cephalonia Island, in W. Greece, which suffered severe damages during the Medicane named after “Ianos”, that affected the Greek territory in September 2020. Most of the steep slope area, which hosts the road that leads to the beach area itself were extensively covered by debris due to mudflows, interrupting aggressively the road connection with the inland network. The use of Unmanned Aerial Systems proved to be an ideal way of mapping quite small areas, with limited access to road networks. The generation of ultra-high resolution spatial products seems to be optimal for mapping and quantifying mass movements that cover areas ranging from less than one square kilometer up to few square kilometers. The aim of such a multi-temporal study, which is described herein, contains aerial image data collection and analysis, before and after the catastrophic event. It is leading to the quantification of the surface topographic changes, by generating a time series of point clouds, after creating several terrain models along with ortho-photo-mosaics, based on Structure-from-Motion photogrammetric techniques. The digital comparison of the co-registered photogrammetric products showed that significant surface alterations have taken place due to the 2020 Medicane. The diachronic point clouds led to the detection and quantification of elevation changes, mainly at the central part of the area of interest, whereas the elevation values of the point clouds were found rather altered, before and after “Ianos”, either positively (deposition) or negatively (erosion), delineating the areas that suffered surface changes.