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.

roberto.tomas@ua 1. Introduction Data collection for kinematic and structural analyses in hills or rock slopes still maintains, nowadays, an important manual component. The set of lithological, structural and characteristic observations of the rock mass, directed to engineering design, is referred to as geomechanics observation point or geomechanical station. The properties and orientation of discontinuities and rock matrix of a geomechanics observation point are obtained in situ, by normalized templates([1]; [2]). Subsequent laboratory/office work determines the resistant properties of the discontinuities, evaluates the geomechanical quality of the rock mass (e.g. using the RMR, Q, or GSI indices) and carries out a census of discontinuities, grouping into main sets. Field data are combined with laboratory results, in situ and geophysical tests, with the objective of elaborating a "geomechanical model" of the rock mass. Field characterization plays an important role in preliminary studies and, in many cases, is the only information available in the first stages of investigation and project development. Traditionally, rock mass field data collection has been carried out by physically accessing the slope. However, remote acquisition techniques have provided a new perspective. The main two remote data collection techniques are Interferometric Synthetic Aperture Radar -InSAR-and Light Detection and Ranging -LiDAR [3], [4].InSAR enables high precision measurements of terrain surface movements, and is usually applied to monitor and detect landslides. LiDAR provides a 3D point cloud of the This is a previous version of the article published in

Characterisation of a rock mass requires data from the intact rock along with the discontinuities. Assuming that the discontinuities are planar, its characterisation requires its number and orientation. This leads to the analysis of the normal spacing, the persistence and the roughness, among others. The geometrical analysis of the surface enables the calculation of the parameters to characterise the discontinuities, and the use of digital datasets enhance them. Remote sensing techniques, such as the Terrestrial Laser Scanning (TLS) instruments of Structure from Motion (SfM) technique, provide 3D point clouds that enable the geometrical analysis. The scientific community has been testing both techniques since the 2000s, and companies are introducing their use in their workflows. However, the cost of the TLS instrument could still be a barrier to its use to most scholars. Because of this, the community shows a growing interest in Remotely Piloted Aircraft Systems (RPAS) equipped with digital cameras or in smartphones equipped with high-quality cameras to capture digital datasets of rocky slopes. The SfM workflow processes the captured images, reconstructing the rocky slope through a 3D point cloud and textured meshes. Although previous studies show that the SfM-derived point clouds present less quality than TLS-derived datasets in terms of accuracy, the use of SfM is still of interest because of its cost. In 2020 Apple launched the Iphone-12 device, which is equipped with a LiDAR sensor that is not used to capture the surface coordinates but to enhance the photo’s quality. Since then, the community has developed several applications to reconstruct 3D surfaces using this device. This leads to consider this device as an intermediate option between the TLS and SfM to characterise rocky slopes and their discontinuities. In this communication we explore the digitalisation of a rocky slope via TLS instruments, SfM technique and using the Iphone-12 device. It comprises a 26 meter high mechanically excavated rocky slope in Cretaceous marlstones and limestones. To capture the surface, we used three configurations, and we found that to scan ground surface the distance device-surface had to be less than 3 meters. The discontinuities are characterised using the three sources of information using the DSE software. The results show a promising match compared to the TLS or SfM. This evidences that these devices will soon be widely employed for evaluating rocky slopes.

This paper is focused on the Middle Paleolithic rock shelter called “Abrigo de San Lázaro”, placed in the Eresma River valley (Segovia, Spain). In this area, a multisource geomatic approach is used. On the one hand, the external envelope of the shelter has been digitalized by the means of an efficient combination between aerial photogrammetry and laser scanning (static and mobile). On the other hand, the ground penetrating radar and the electric tomography were used with the aim of evaluating the inner disposition of the shelter. The combination of both digitalization (external and internal) has allowed for improving the knowledge of the site characteristics that, in turn, will facilitate the future excavation works. The results of these studies allow archaeologists to know new data for a better understanding of the site formation (geology of the site, sedimentary potential, rock shelter dimensions, etc.) and the events that took place in it (knowing its historical evolution, especially the interaction between man and the environment). Additionally, the information obtained from these studies is very useful to plan future excavation works on the site.

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