## 2 Materials and Methods
### Data Collection and Preprocessing
#### 2.2.2 Digital Elevation Models  
Digital Elevation Models (DEMs) and their derived products (e.g., slope, hillshade) are a crucial source of data regarding spatial and environmental analysis, including coastal vulnerability to sea level rise scenarios [48; 49; 50; 51]. Several global Digital Elevation Models (DEM) or Digital Terrain Models (DTM) are openly available at a resolution of approximately 30 m, including global models, for example, ASTER-GDEM [52; 53], NASADEM [54], AW3D30, SRTM 1-arcsecond v.3, Copernicus DEM. The ASTER-GDEM is a cooperation product between the United States National Aeronautics and Space Administration (NASA), and the Japanese Ministry of Economy, Trade and Industry (METI) [55]. It covers 99% of the land surface of the Earth from latitude 83\({}^{\circ}\) North to 83\({}^{\circ}\) South. In 2019, GDEM v.3 was published, using a thorough automated and manual anomaly correction program in addition to several hundred thousand extra scenes that were incorporated to enhance quality and accuracy [55]. Its positional accuracy varies between 18 and 20 m, while its vertical accuracy varies between 15 and 16 m.  
NASADEM is an updated version of the DEM product generated through the Shuttle Radar Topography Mission, initially published in January 2019. Using enhanced algorithms, the SRTM raw signal data were reprocessed, combined with additional information mainly from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Ice, Cloud and Land Elevation Satellite (ICESat) Geoscience Laser Altimeter System (GLAS) instruments [54]. These cover 80% of the land surface of the Earth from latitude 61\({}^{\circ}\) North to 56\({}^{\circ}\) South. Their positional accuracy is around 20 m, while their vertical accuracy is around 10 m [56]. The Advanced Land Observing Satellite (ALOS)-AW3D30 was produced by the Japanese Aerospace Exploration Agency (JAXA). The ALOS world 3D generated the ALOS world 3D-30 m mesh. With a grid size of 5 m, the ALOS world 3D is a high-resolution DSM that spans the latitude regions of \(+/-80\) degrees. Resampling \(7\times 7\) pixels from the AW3D DSM dataset produced the ALOS World 3D 30 m DSM [57]. AW3D30 DSM's attained accuracy and found that it can produce a height RMSE of 4.4 m [57]. The 5 m dataset is  
Figure 2: Global, European and national coastline datasets’ deviation in the Island of Aegina, Greece. available under a commercial license; however, a 30 m resolution dataset is openly available (AW3D30). The Shuttle Radar Topography Mission (SRTM) was carried out on 11-22 February 2000 using the space shuttle Endeavour. The first nearly worldwide set of land elevations was created through the participation of the National Aeronautics and Space Administration (NASA), the National Geospatial-Intelligence Agency (NGA), and several international partners to acquire radar data. The SRT Mission used two Synthetic Aperture Radars (SAR), a C band system (5.6 cm/C radar), and an X band system (3.1 cm, X radar) [58]. The mission completed 176 orbits around the Earth (16 orbits per day for 11 days) and collected data points per every 1-arc second (approximately 30 m) covering 80% of the Earth's surface between 60\({}^{\circ}\) North and 56\({}^{\circ}\) South latitude [58]. SRTM's absolute geolocation error varies from 7.2 to 12.6 m, and the absolute height error varies from 5.6 to 9.0 m, while the relative height error varies between 4.7 and 9.8 m [59]. Copernicus DEM is a Digital Surface Model depicting the Earth's entire surface, including buildings, vegetation, and infrastructure [60]. The DEM was developed based on an edited DSM, entitled WorldDEMTM, which includes flattening water bodies and consistent river flows. An additional editing process has been applied regarding features such as airports, shores, coastlines, etc. A public-private cooperation between Airbus Defence and Space and the German Aerospace Center led to the collection of radar satellite data used to create the WorldDEM product [61].