Digital landform reconstruction using old and recent open access digital aerial photos

Abstract

Technological progress in remote sensing has enabled digital representation of terrain through new techniques (e.g. digital photogrammetry) and instruments (e.g. 3D laser scanners). However, the use of old aerial images remains important in geosciences to reconstruct past landforms and detect long-term topographic changes. Administrations have recently expressed growing interest in sharing photogrammetric datasets on public repositories, providing opportunities to exploit these resources and detect natural and anthropogenic topographic changes. The SfM-MVS photogrammetric technique was applied to scanned historical black and white aerial photos of the Serra de Fontcalent (Alicante, Spain), as well as to recent high-quality digital aerial photos. Ground control points (GCPs) extracted from a LiDAR-derived threedimensional point cloud were used to georeference the results with non-linear deformations. Two point clouds obtained with SfM-MVS were compared with the LiDAR-derived reference point cloud. Based on the result, the quality of the models was analysed through the comparison of the stages on stable areas, i.e., lands where no variations were detected, and active areas, with quarries, new infrastructures, fillings, excavations or new buildings. This study also indicates that errors are higher for old aerial photos (up to 5 m on average) than recent digital photos (up to 0.5 m). The application of SfM-MVS to open access data generated 3D models that enhance the geomorphological analysis, compared to stereophotogrammetry, and effectively detected activities in quarries and building of landfills.

Landslide Scaling: A Review

“…LIDAR (Light detection and ranging) surveys (e.g., Roering et al, ), digital photogrammetry (e.g ., Liu et al, ; Romeo et al, ), and satellite surveys (e.g., Wang et al, ) are being used to create digital elevation models (DEMs) to study landslide events. Pre‐ and post‐event DEMS can be compared to obtain three‐dimensional estimates of volumetric change (e.g., Bossi et al, ; Calista et al, ; Fanos & Pradhan, ; Riquelme et al, ). As methods improve and additional pre‐ and post‐event DEMs are collected for more regions, there will be a reduced need to use landslide area measures to estimate volume measures.…”

Identification of Micro-Scale Landforms of Landslides Using Precise Digital Elevation Models

“…A description of the options is available in the Photoscan manual [37]. Detailed descriptions of the 3D reconstruction process in the Photoscan software are described in various studies [16,38,39].…”

“…The Lasnoise tool was used to exclude low noise points [class 7] because, in case of ground point derivation in further steps, it is recommended to leave out low noise points [39]. Clusters of low points occur frequently in image areas that were strongly shadowed, which was the case of the RPAS photographing of the landslide in the rugged terrain under dense forest canopy.…”

“…The Lasground_new tool was used for bare-earth extraction; it classifies points into ground points (class = 2) and non-ground points (class = 1), and we computed the height of each point (without replacing -z) above the ground [39] in cases of the RPAS and the SfM CRP data.…”

“…The Lasheight_classify tool computes the height of each point above the ground and creates normalized point clouds in the selected height or interval of heights [39]. This tool was used for the processing of RPAS point clouds because photogrammetric scanning was done above a dense canopy of trees, locally, with a lower level of shrubs and where bare-earth was not visible.…”