New approach for photogrammetric rock slope premonitory movements monitoring / María Amparo Núñez Andrés, Albert Prades Valls, Gerard Matas Casado, [et al.]



En: Remote sensing. vol. 15, núm. 2 (Gener 2023), article 293

An automated, fixed-location, continuous time-lapse camera system was developed to analyze the existence of rockfall precursory movements and quantify volume changes after detachments. It was implemented to monitor the basaltic formation on which Castellfollit de la Roca village is built. Due to the geometrical conditions of the area, the camera system consists of three digital cameras managed by a control unit that contains a Raspberry Pi 4 microprocessor. Images taken every day are sent to a server for processing. A workflow has been developed to work with a set of images with an irregular time interval to detect precursor movement. The first step consists of matching the images with a reference master image and filtering the vegetation to improve the process using a mask obtained by a green leaf index (GLI) index. Then, the adjusted images are used for a forward-backward correlation process carried out to detect movements. If movement is detected, a 3D model is built using structure from motion (SfM) to quantify the movements. The system has been working since September 2021. During this period, movements from 0.01 to 0.5 m and several rockfalls of a small volume have been detected.

Implementation of a fixed-location time lapse photogrammetric rock slope monitoring system in Castellfollit de la Roca, Spain / Gerard Matas Casado, Albert Prades Valls, María Amparo Núñez Andrés, [et al.]



En: Joint International Symposium on Deformation Monitoring. "5th Joint lnternational Symposium on Deformation Monitoring: proceedings: 20-22 June 2022, Polytechnic City of lnnovation, Valencia (Spain)". València : Editorial UPV, 2022. p. 63-68


When monitoring deformations in natural hazards such as rockfalls and landslides, the use of 3D models has become a standard. Several geomatic techniques allow the generation of these models. However, each one has its pros and cons regarding accuracy, cost, sample frequency, etc. In this contribution a fixed-location time lapse camera system for continuous rockfall monitoring using photogrammetry has been developed as an alternative to Light Detection and Ranging (LiDAR) and ground-based interferometric synthetic-aperture radar (GB-InSAR). The usage of stereo photogrammetry allows the obtention of 3D points clouds at a low cost and with a high sample frequency, essential to detect premonitory displacements. In this work the designed system consists of three digital single-lens reflex (DSLR) cameras which collect photographs of the rock slope daily controlled by a Raspberry Pi computer using the open-source library gPhoto2. Photographs are automatically uploaded to a server using 3G network for processing. This system was implemented at Castellfollit de la Roca village (Girona province, Spain), which sits on a basaltic cliff that has shown significant rockfall intensity in recent years. The 3D models obtained will allow monitoring rockfalls frequency, premonitory displacements, and calculate the erosion rate of the slope. All technical decisions taken for the design and implementation on this specific site are discussed and first results shown.