Application of Structure from Motion Techniques Using Historical Aerial Images, Orthomosaics, and Aerial LiDAR Point Cloud Datasets for the Investigation of Debris Flow Source Areas

Detecting topographic change in mountainous areas using historical aerial imagery is challenging due to complex terrain and variable data quality. This study evaluates the potential of Structure from Motion (SfM) for deriving 3D information from archival photograms in the Rabbia basin (Central Italian Alps), a catchment with a well-documented history of debris flow activity. The aim is to assess the impact of input configurations and photogrammetric processing strategies on the quality and interpretability of 3D reconstructions from historical aerial imagery, as a basis for further geomorphological analyses. A 1999 aerial dataset was processed via SfM workflow to generate a point cloud and orthomosaic, and then co-registered with a 2021 LiDAR-derived dataset. Multi-temporal analysis was conducted using point cloud distance computations and visual interpretation of orthomosaics. Additional aerial images spanning nearly 80 years expanded the temporal scale of the analysis, providing valuable retrospective insight into long-term terrain evolution. The results, although considered semi-quantitative due to data quality limitations, are consistent with geomorphological trends in the area. The study confirms that historical SfM-derived products, when supported by robust co-registration and quality checks, can contribute to sediment dynamics and hazard evaluation in alpine environments, though result interpretation should remain cautious due to dataset-specific uncertainties.