Correlation of multi-temporal ground-based optical images for landslide monitoring

The objective of this work is to present a low-cost methodology to monitor the displacement of continuously active landslides from ground-based optical images analyzed with a normalized image correlation technique. The performance of the method is evaluated on a series of images acquired on the Super-Sauze landslide (South French Alps) over the period 2008-2009. The image monitoring system consists of a high resolution optical camera installed on a concrete pillar located on a stable crest in front of the landslide and controlled by a datalogger. The data are processed with a cross-correlation algorithm applied to the full resolution images in the acquisition geometry. Then, the calculated 2D displacement field is orthorectified with a back projection technique using a high resolution DEM interpolated from Airborne Laser Scanning (ALS) data. The heterogeneous displacement field of the landslide is thus characterized in time and space. The performance of the technique is assessed using differential GPS surveys as reference. The sources of error affecting the results are then discussed. The strongest limitations for the application of the technique are related to the meteorological, illumination and ground surface conditions inducing partial or complete loss of coherence among the images. Small movements of the camera and the use of a mono-temporal DEM are the most important factors affecting the accuracy of the ortho-rectification of the displacement field. As the proposed methodology can be routinely and automatically applied, it offers promising perspectives for operational applications like, for instance, in early warning systems. © 2012 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS)

A multidisciplinary approach to landslide structure characterization: integration of seismic tomography survey and high resolution LiDar data with the Sloping Local Base Level method.

International audienceA challenge to progress in the understanding of landslides is to precisely define their 3D geometry and structure as an input for volume estimation and further hydro-mechanical modelling. The objective of this work is to present a multidisciplinary approach to the geometrical modelling of the La Valette landslide by integrating seismic tomography survey (P and S wave) and high resolution LiDar data with the Sloping Local Base Level (SLBL) method. The La Valette landslide, triggered in March 1982, is one of the most important slope instability in the South French Alps. Its dimensions are 1380 m length and 290 m width, and the total volume is estimated at 3.5 106 m3. Since 2002, an important activity of the upper part of the landslide is observed, and consisted mainly in the retrogression of the crown through the opening of an important fracture over several meters and rotational slumps. The failed mass is currently loading the upper part of the mudslide and is a potential threat for the 170 residential communities

Imagerie multi-paramètres et multi-résolutions pour l'observation et la caractérisation des mécanismes de glissements-coulées

Controlling factors (predisposition, triggering) of landslides as well as their mechanism and kinematic behaviour can be extremely heterogeneous and interact on very versatile time constants. Numerous gaps exist in the evaluation of the hazard associated with this process, in particular for slow landslides which can evolve into faster slides. Indeed, landslides show some behaviour which is very variable in time and space which is characterized by a large range of displacement rates (from less than 1 centimetre per year to a few meters per day) and the presence of irregularities and large heterogeneities in the distribution of their petrophysical properties. Classical techniques of observation and investigation allow us to get only localized information which is not enough to quantify the time and spatial variability. As a result of which landslide numerical models are calibrated and validated over a limited amount of data. Recent developments in multiparameter geophysical imaging allowed some improvements in the direct and indirect acquisition of data on the deformation (photogrammetry, images correlation, laser scanner) and petrophysical parameters (electric tomography and seismic refraction). Although not as precise as the classical techniques, they have the advantage of providing multi-scaled and spatially distributed information. A major difficulty is to combine this spatial information to the ones obtained with classical technologies (GPS, extensometry, piezometry, geotechnology) and integrate them into a conceptual model coherent for the modelisation. Some scientific works have begun to combine different approaches obtained from field observations (geomorphology, geology) and instrumental data (hydrogeophysics, photogrammetry, laser scan). The objective is to develop methodologies which allow one to spatially determine the diverse major characteristics of landslides (intern structuration, hydrologic behaviour, kinematic behaviour, deformation mechanism). A conceptual model of the functioning and modelling of the hydro-mechanical behaviour of landslides with Z-soil and Slow-Mov codes is proposed. The sites selected for our analysis are the marly landslides of Super-Sauze and La Valette in the basin of Barcelonnette (Alpes-de-Haute-Provence). The research is presented in four parts and the objectives are as follows: 1. To characterize the internal structure and 3D geometry of landslides with the help of geophysical, geotechnical and geomorphologic data ; 2. To propose a hydrological conceptual model of the non saturated zone followed by temporal and spatial monitoring of electric resistivity and piezometric data analysis ; 3. To characterize the kinematics of landslides from terrestrial remote sensing platforms (photogrammetry and laser scan) combined with aerial platforms and differential GPS monitoring. 4. To identify the thresholds of hydrological and kinematics regime changes with numerical modelling. The results highlight the vast scope of application of the main imaging technologies for the investigation of landslides and allow us to define their limitations of use. Some future research will develop these various methodologies for surveillance purposes and to improve the predictive capabilities of the hazard.Les facteurs de contrôle (prédisposition, déclenchement) des glissements de terrain, leurs mécanismes et leurs comportements cinématiques peuvent être extrêmement hétérogènes et interagir sur des constantes de temps très variées. De nombreuses lacunes existent dans l'évaluation de l'aléa associé à ces processus, en particulier pour les glissements lents qui peuvent évoluer en coulées rapides. Les glissements-coulées présentent en effet des comportements très variables dans le temps et dans l'espace caractérisés par un large spectre de vitesses de déplacement (de moins de un centimètre par jour à plusieurs mètres par jour) et la présence de discontinuités et de grandes hétérogénéités dans la répartition de leurs propriétés pétro-physiques. Les techniques d'observation et d'investigation classiques permettent d'obtenir des informations ponctuelles qui ne sont pas suffisantes pour quantifier ces variabilités spatiales et temporelles. Une des conséquences est que, bien souvent, les modèles numériques de glissement ne sont calés et validés que sur un nombre limité d'observations in-situ. Les développements récents en imagerie géophysique multi-paramètres ont permis de progresser dans l'acquisition directe et indirecte de données sur la déformation (photogrammétrie, corrélation d'images, scanner laser) et les paramètres pétro-physiques (tomographie électrique et sismique réfraction). Malgré une précision souvent inférieure à celles des techniques classiques, elles ont l'avantage de fournir des informations multi-échelles et distribuées spatialement. Combiner ces informations spatiales à celles obtenues par les techniques classiques (GPS, extensométrie, piézométrie, géotechnique) et les intégrer dans un modèle conceptuel cohérent pour la modélisation numérique constitue une difficulté majeure. Des travaux scientifiques ont été engagés en combinant différentes approches issues d'observations de terrain (géomorphologie, géologie) et de données instrumentales (hydrogéophysique, photogrammétrie, scanner laser). L'objectif est de développer des méthodologies permettant de déterminer spatialement les différentes caractéristiques majeures des glissement-coulées (structuration interne, comportement hydrologique, comportement cinématique, mécanisme de déformation). Un modèle conceptuel de fonctionnement et des modélisations du comportement hydro-mécanique des glissements-coulées avec les codes Z-Soil et Slow-Mov sont proposés. Les sites d'étude retenus pour notre analyse sont les glissements-coulées marneux de Super-Sauze et de La Valette dans le Bassin de Barcelonnette (Alpes-de-Haute-Provence). Les travaux de recherche sont présentés en quatre parties dont les objectifs sont : 1. De caractériser la structuration interne et la géométrie 3D des glissement-coulées à l'aide de données géophysiques, géotechniques et géomorphologiques ; 2. De proposer un modèle conceptuel hydrologique de la zone non saturée par suivi temporel et spatial de résistivités électriques et par l'analyse de données piézométriques ; 3. De caractériser la cinématique des glissements-coulées à partir de plateformes terrestres de télédétection (photogrammétrie et scanner laser) combinées à des plateformes aériennes et à des suivis par GPS différentiel ; 4. D'identifier des seuils de modifications de régimes hydrologiques et cinématiques par la modélisation numérique. Les résultats soulignent le vaste champ d'application des principales techniques d'imagerie pour l'investigation des glissement-coulées et permettent de définir leurs limites d'utilisation. Des études futures devraient permettre de développer ces différentes méthodologies à des fins opérationnelles de surveillance et pour améliorer les capacités de prédiction de l'aléa

Acquisition of airbone LiDAR data from helicopter at the La Valette landslide.

OLYMPUS DIGITAL CAMER

Image-based correlation of Laser Scanning point cloud time series for landslide monitoring

International audienceVery high resolution monitoring of landslide kinematics is an important aspect for a physical understanding of the failure mechanisms and for quantifying the associated hazard. In the last decade, the potential of Terrestrial Laser Scanning (TLS) to monitor slow-moving landslides has been largely demonstrated but accurate processing methods are still needed to extract useful information available in point cloud time series. This work presents an approach to measure the 3D deformation and displacement patterns from repeated TLS surveys. The method is based on the simplification of a 3D matching problem in a 2D matching problem by using a 2D statistical normalized cross-correlation function. The computed displacement amplitudes are compared to displacements (1) calculated with the classical approach of Iterative Closest Point and (2) measured from repeated dGPS observations. The performance of the method is tested on a 3 years dataset acquired at the Super-Sauze landslide (South French Alps). The observed landslide displacements are heterogeneous in time and space. Within the landslide, sub-areas presenting different deformation patterns (extension, compression) are detected by a strain analysis. It is demonstrated that pore water pressure changes within the landslide is the main controlling factor of the kinematics

Target Detection and Tracking of moving objects for characterizing landslide displacements from time-lapse terrestrial optical images

International audienceTerrestrial Optical Photogrammetry (TOP) is a low-cost monitoring technique that is commonly used in change detection studies. For landslide monitoring, image correlation techniques are frequently used to generate Digital Surface Models (DSMs) from stereo-pairs or to measure the 2D surface displacement field from single-view time-lapse sequences. Image correlation allows for detecting spatially continuous displacement fields at a sub-pixel precision. The technique, however, has several limitations for assessing displacement because 1) of its sensitiveness to changes in texture, shape and radiometry in the image pile, 2) of the need of spatially regular sampling grids, and 3) of possible high computation time that can impede the processing of large image datasets.To address these limitations, an alternative and complementary approach based on a Target Detection and Tracking (TOT) algorithm is proposed for a rapid calculation of the displacement of targets in image time series. The TDT code, developed as a MATLAB-based tool, is able to track natural or man-made targets. The precision of the TDT code is assessed using several image time series acquired at the Super-Sauze landslide (Southern French Alps) and compared to ground based measurements. The computed relative accuracy is between 10(-3) and 10(-4) (5 cm at a distance of 115 m). Although the TOT approach does not provide spatially continuous information, it provides 1) a quantification of the object displacements at the same order of precision as image correlation (sub-pixel accuracy) and 2) information in regions where image correlation fails because of too large ground displacements. A sensitivity analysis reveals that the major sources of uncertainty are camera movement and/or lens distortion and not the TOT method itself

CERN Past performance and future prospects

ESRC End of Grant ReportSIGLEAvailable from British Library Document Supply Centre- DSC:8318.1714F(ESRC-G--00/23/0076)fiche / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Characterizing landslides through geophysical data fusion: Example of the La Valette landslide (France)

International audienceMany studies show that certain geophysical methods, such as seismic and electrical-resistivity imaging, appear to be well adapted for investigating the internal structures of landslides and understanding the related hydro-mechanical mechanisms. These are methods that allow the direct and non-intrusive measurement of acoustic (P) and shear (S) wave velocities and electrical resistivity (ρ), which are three physical parameters considered as essential for estimating the mechanical properties of moving reworked material. We applied these techniques to the La Valette landslide (Southern French Alps), a typical example of an intra-material landslide, carrying out measurements simultaneously along two profiles, 400 m and 300 m long and respectively perpendicular to and along the slide direction. We then used suitable inversion algorithms to estimate both the P- and S-wave velocity fields and the electrical resistivity field from the recorded data. The results, aided by field surface observations, show that a correlation exists between the state of the material and the seismic-velocity and/or electrical-resistivity data, thus confirming that the simultaneous use of the two methods provides complementary information on the geomechanical behavior of the landslide. More particularly, the seismic data provide information on fissure density variations and the presence of shear-bent material, whereas the electrical resistivity data provide information on the groundwater content. To enable a more integrated petrophysical interpretation, we applied a data-fusion strategy based on fuzzy subsets to the geophysical datasets. Through combining the tomograms we identified a surface layer of soft material along the two profiles; the bottom of this layer was also recognized in a borehole. From a methodological point of view, the results show the applicability of adopting geomechanical hypotheses as inputs of geophysical data fusion for identifying areas where sediment mobilization could occur