The integrated use of LiDAR and photogrammetric techniques by the UAS platform for the mapping of rockfall processes in Ischia Island (Italy)

The following work focuses on the surveys that were carried out using optical sensors (photogrammetry) and LiDAR mounted on UAS platforms. The processing of the acquired images provided the necessary information for the development of high-precision digital terrain models that can be used as a basis for the subsequent modeling of the stability analysis of collapse phenomena with STONE, a three-dimensional rockfall simulation model. These surveys allowed us to localize the possible detachment sources and the inclusion of scenario-based seismic shaking as a trigger for rockfalls.

The areas filmed fall almost exclusively along the north-western slope of Mt. Epomeo and more precisely in the areas identified as locality Falanga (32 ha) and locality Frassitelli (123 ha) in the territory of the Municipality of Forio (Napoli) and only marginally in the Municipality of Serrara Fontana (Napoli). The slope surveyed has two distinct morphologies: 1) the north-west oriented sector (Falanga) delimited by extremely steep walls and by cliffs with variable vertical development, at the base of which there is a large sub-flat area delimited to the north by a new sudden jump in slope; 2) in the west sector (Frassitelli) the slope is instead more rounded, even if in various points there are areas with steep slopes and strongly fractured cliffs; this side is characterized by the presence of numerous tuff blocks, even of large dimensions, which have stopped at various altitudes after having detached themselves from the overlying sub-vertical walls.

We also used data from the Geoportale Nazionale Italiano managed by the Ministry of Environment and provided different kinds of spatial data. In particular, the archive contains an extensive LiDAR survey covering a substantial portion of Italy, with data stored at the intermediate processing level. For this research, we selected point clouds covering the Ischia island and we interpolated separately the two point clouds, using the module specifically designed to perform surface interpolation from vector points mapped by splines, within the GIS platform.

In conclusion, we interpreted the point-to-point difference between DSM and DTM as due to vegetation and exploited this information to infer modifications of ground parameters relevant to the simulations with Stone. We partially took into account disturbances due to the presence of anthropic structures and buildings using additional land cover data, which we correlated with point-to-point DSM – DTM differences.