Julien Travelletti

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

Abstract Very 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.

Monitoring of Earth Surface Motion and Geomorphologic Processes by Optical Image Correlation

Abstract: The detection and quantification of motion of the Earth’s surface are essential for the study and understanding of many geomorphological and geological processes such as tectonics, earthquakes, landslides and ice glaciers, to name a few. The direct measurement of earth displacement and deformation falls into larger discipline of geodesy, which also includes studies of the shape, movement and gravitational field of the Earth. Traditional surveying methods to measure surface motion comprise the use of theodolites, electronic distance meters, total stations and nowadays typically global navigation satellite systems (GNSS). While such methods can provide very precise point-wise measurements, aerial and satellite remote sensing techniques are generally more suitable for measuring dense motion fields of larger and/or inaccessible areas.

Innovative Techniques for the Detection and Characterization of the Kinematics of Slow-Moving Landslides

Remote sensing has been proven useful for landslide studies. However, conventional remote sensing techniques based on aerial photographs and optical imageries seem to be more suitable for detecting and characterizing rapid-moving landslides. This section introduces several innovative remote sensing techniques aiming at the characterization of the kinematics (e.g. displacement pattern, deformation, strain) of slow- to moderate-moving landslides. These methods include Persistent Scatterers Interferometry (PSI), automatic surveying using total station integrated with GPS, Ground-Based Synthetic Aperture Radar Interferometry (GB-InSAR), image correlation of catalogues of optical photographs (TOP) and Terrestrial Laser Scanner (TLS) point clouds. Three case studies, including the Arno river basin (Italy), the Valoria landslide (Italy) and the Super-Sauze landslide (France) are presented in order to highlight the usefulness of these techniques.

Techniques for the modelling of the process systems in slow and fast-moving landslides

This chapter reviews some of the current strategies for landslide modelling. Main physical processes in landslides are first recalled. Numerical tools are then introduced for the analysis of the behaviour of slow- and fast-moving landslides. Representative case studies are introduced through the chapter to highlight how different modelling strategies can be used depending on the physical processes that the modeller wants to take into account.

Innovative Techniques for the Characterization of the Morphology, Geometry and Hydrological Features of Slow-Moving Landslides

In the last 10 years, landslide characterization has benefited from numerous developments in remote sensing, near surface geophysics, instrumentation and data processing. This section highlights various advances and innovative techniques or processing methods to characterize the morphology, structure and hydrological features of landslides. Airborne Laser Scanner (ALS) technique has emerged as a promising tool for characterizing slope morphology, with the perspective of automatic detection of landslide-affected areas. Combining ALS-data DTM with geophysical and geotechnical information has allowed to reconstruct the 3D landslide geometry considering data uncertainty and resolution. This is a significant forward step in landslide investigation. Of major importance is also the detection and monitoring of water infiltration in the sliding masses, using indirect prospecting techniques such as ERT and distributed temperature sensing (DTS) using fibre-optic cables. These new techniques could be a major help in understanding the water paths and in designing appropriate remediation systems. Finally, although most of these results have been obtained in clayey landslides, the applied methods can be extended to other landslide types, with some technical adaptations.

Mountain risks: from prediction to management and governance

One of the most interesting aspects of large-scale funding from the European Union over the last 30 years has been the potential to create extensive, international, multidisciplinary research programs that tackle substantial problems facing society. Whilst in the early days, these programs mostly consisted of teams of experienced researchers, more recently, the Marie Curie Intensive Training Network (ITN) schemehas facilitated thedevelopment of teams of early-career researchers: students undertaking doctoral research and those in the immediate postdoctoral phase. These ITNs provide a double benefit, not only permitting large teams of dedicated researchers to tackle in detail an important topic, but also offering the opportunity to develop a group of researchers who have been trained to a very high level in that specific area. The evaluation of risk in high mountains is one such substantial area, and this volume represents the outcome of a recent ITN, the Mountain Risks consortium, which ran from 2007 to 2011, with 14 partners. The program sought to provide research and training on mountain hazards and their associated risks and management strategies. The editors of the book are well known in this field, and most of the papers have been written by a combination of established experts (the supervisors) and earlycareer researchers (the students and postdoctoral researchers). The evaluation of mountain risk is complex. The book is based on a conventional (but almost universally adopted) approach to risk assessment: a simple equation that views risk as the product of the hazard, the vulnerability of the assets in question, and their exposure to the peril. Such an approach is best suited to simple physical assets such as buildings and roads. However, there is increasing concern that this type of approach struggles to deal with the complex nature of risk, especially for remote communities in high mountain areas. Risk in such an environment is a nebulous, multifaceted entity that, critically, is highly dynamic. Thus, the vulnerability of a community depends not only on its physical attributes but also on the degree of social cohesion, from the local to the national level. The risk to a particular community may vary greatly in time, as social conditions and structures change: For example, losses to landslides in Nepal increased substantially during the civil war in the early part of the last decade, when social cohesion collapsed in remote mountain communities. Capturing this in a conventional risk assessment is extremely difficult. Inevitably, the 15 papers are a slightly eclectic mix, but the quality is high. A notable strength is that most draw heavily upon the literature reviews that the doctoral students had undertaken as a part of their theses, providing a very useful oversight of the state of knowledge in each area. Some of the papers examine in some detail specific aspects of mountain risks, such as the use of ground-based interferometric synthetic aperture radar (InSAR) for landslide monitoring, whilst others are more broadly based reviews of key topics. The most interesting passages are those that focus on the vulnerability and exposure aspects of the risk equation, although the approach is generally quite conventional. There are a number of useful chapters that consider how vulnerability and exposure can be built into a quantitative risk evaluation, and on the implications of the outcomes for the management of those risks. Some aspects of the volume are a little frustrating. Critically, most of the hazards that are considered are those associated withmass movements, from individual rockfalls to large-scale landslides. Other mountain risks, such as snow avalanches, glacial lake outbursts, earthquakes, and flash floods, are barely considered. Thus, the book is perhaps slightly poorly titled. The book has a very strong European focus, largely with a western European slant. It is perhaps a shame that more consideration is not given to approaches in, for example, Canada and Japan, both of which have been innovative in this field. Finally, a few of the chapters are disappointingly short. For example, a chapter on lessons learnt from past disasters is potentially very interesting; that the text in the chapter itself, excluding the abstract, references, diagrams, etc, is only 5 pages feels slightly disappointing. In summary, this is a very interesting and useful volume that represents an important contribution to the field. The great strengths are the ways in which the book integrates both natural and social sciences and provides useful reviews of the state of the art in a wide variety of areas of risk assessment and management. Several of the chapters that examine different aspects of risk assessment are very valuable and deserve to be widely read. It will be of interest to both the research and the practitioner communities. However, the most important outcome from the ITN Mountain Risks consortium is probably the development of a large number of early-career professionals with high-level skills in the field of mountain risk. This book is a testament to their knowledge and skills.