## 2 Materials and Methods  
### Case Studies  
The selection of research areas was based on the criterion of heterogeneity in terms of slope, land cover, vegetation coverage, etc. Thus, four different landslides were set as case studies. We also surveyed a flat industrial area for validation purposes (Figure 1) (Table 1). In order to eliminate the influence of vegetation height on DSM production, the study areas presented, in general, with low and sparse vegetation, as described in Table 1.  
The first landslide area is located close to the village of Moira, within Western Greece. The landslide occurred on 20 January 2017 on a mountainous, steep slope, covering an area of approximately 65,569.20 m\({}^{2}\). The landslide material was spread 300 m in length and 300 m in width and it was geologically structured from flysch, limestone, and loose cherts. It was characterized as a complex slide, based on the different lithologies--silicate and/or silicate lithology was presented in the northwestern part, while limestones were detected in the southeast. The occurrence of the landslide was related to geological factors (flysch lithology), as well as to the rapid snow melting. It has been demonstrated that the increase of the water content of clay soils (flysch) reduces the shear strength of soils, acting as a triggering factor for the occurrence of landslides [29].  
The destruction of the road connecting the village of Moira with the city of Patras, as well as a significant change in the local landscape, were the main consequences of the landslide.  
The second landslide took place in November 2015 on the Egkremni beach on the island of Lefkada; it was classified as a debris slide. The Ionian Islands constitute the northwestern part of the Hellenic arc, which is considered as a site of complex continent-continent to continent-ocean convergent plate margins. The Cephalonia Transform Fault Zone (CTFZ) is recognized as the major tectonic structure of the site and is responsible for the particularly active seismicity in the wider area. In addition, another fault, named Athani, is detected ashore, shaping the west coast of Lefkada island [30; 31]. The Athani fault, along with smaller, parallel faults with similar kinematics, form steep slopes, which are an ideal site for the occurrence of landslides during seismic events [32]. On 17 November 2015, a 6.5 magnitude earthquake struck the west coast of the island, causing a series of landslides on the cliffs [33; 34].  
Another active continental region, in terms of tectonics and seismicity, is Northern Peloponnese, due to the fast-extending rift of the Gulf of Corinth. This third area of interest is located close to the village of Kato Zachlorou within Western Greece. The first mass movements at the specific area occurred in April 2019, while the main event, consisting of rock falls and earth flows, took place on 4 April 2020. The repetitive sliding episodes were strongly associated with the increase of the water content of the clay soils, due to intense rainfall [29].  
The fourth area of interest includes a landslide located in a semi- mountainous village of Western Greece named Messarista. Extremely heavy and prolonged rains hit the wider region on 11 December 2021, acting as a main triggering factor for the occurrence of a series of landslides in different places throughout the region, as well as within the village of Messarista. The phenomenon is still ongoing and is being monitored by local authorities, while the landslides were classified as earth slides and earth flows.  
Finally, a flat industrial area, covering part of the new port of the city of Patras, was chosen for the validation of the results, due to the past view on photogrammetry, in which flat areas were surveyed using nadir imagery solely.