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Synthetic Aperture Radar (SAR) acquisition can be performed from satellites or from the ground by means of a so- called GB-InSAR (Ground-Based Interferometry SAR), but the signal emission and the output image geometry slightly differ between the two acquisition modes. Those differences are rarely mentioned in the literature. This paper proposes to compare satellite and GB-InSAR in terms of (1) acquisition characteristics and parameters to consider; (2) SAR image resolution; (3) geometric distortions that are foreshortening, layover and shadowing. If in the case of satellites SAR, the range and azimuth resolutions are known and constant along the orbit path, in the case of GB-InSAR their values are terrain-dependent. It is worth estimating the results of a GB-InSAR acquisition one can expect in terms of range and azimuth resolution, Line of Sight (LoS) distance and geometric distortions to select the best installation location when several are possible. We developed a tool which estimates those parameters from a Digital Elevation Model (DEM), knowing the GB-InSAR and the Slope of Interest (Sol) coordinates. This tool, written in MATLAB, was tested on a simple synthetic point cloud representing a cliff with a progressive slope angle to highlight the influence of the Sol geometry on the acquisition characteristics and on two real cases; cliffs located in Switzerland, one in the Ticino canton and on in the Vaud canton. [ABSTRACT FROM AUTHOR]

This paper presents a new method to estimate a landslide failure surface and its volume based on a digital elevation model (DEM) using spline curves by assuming values of the tangent of the failure surface along with transversal vertical profiles. The model will give the depth of the probable failure surface plotted using the 2D grid function. We can easily visualize the results by running the codes; the display will show the step-by-step processes involved. The model requires fundamental data inputs, which are readily available online throughout the world, such as a DEM of the study area and a KML file of contour limits of the landslide as input. The calculation procedure is simple; it evaluates the depth of the failure surface at each point of the grid. The cross-section for each point is estimated perpendicular to the slope line joining the highest elevation point and the lowest elevation point within the contour limits. A cubic spline curve is calculated using two endpoints and the first derivative at these points. The Z value is calculated using these parameters at each grid point (centre of a grid), and finally, a 3D failure surface is generated, enabling the volume calculation. MATLAB code has been written to execute this process automatically. This model can easily use input data with very little fieldwork, and the processing can produce a result in a few minutes. We can enrich a real scenario by imposing more constraints on the variation in the cross-section angle based on the limit of the landslide using field measurements. This model is also helpful in predicting the area affected by the mass of the failure surface, and we can determine a predefined hazard zone to avoid any casualties in the future. [ABSTRACT FROM AUTHOR]

A new inventory of 66 small and shallow landslides within six pilot areas was created based on a high-resolution digital elevation model in the canton of Vaud in Switzerland. The geometrical characteristics of the landslides were recorded (i.e. surface area, maximum thickness and length), and the volumes were estimated. These data permitted the development of a model that provides the probability for a landslide to possess a maximum thickness or volume smaller than a given value based on the landslide horizontal surface area. The results are compared with three existing power-law relationships of surface area–volumes. This new approach constitutes a way to improve the quantification of the uncertainty of volume and maximum depth estimations for small and shallow landslides. [ABSTRACT FROM AUTHOR]

Reconstructions of failure surfaces (prior to potential landslides or after their release), landslide deposits, or other palaeotopographic features are important for hazard and erosion assessment. The volumes involved in landslide and failure surfaces constrain the propagation of a landslide, and knowledge of the past topography helps us to understand these hazards. Some methods exist to characterise landslide geometry, but these methods usually require monitoring information. This study tries to assess the validity of the sloping local base level (SLBL) method for this purpose. Two sets of airborne lidar digital elevation models (DEMs) of the Kii Peninsula (Japan) are used: the first one was acquired before Typhoon Talas, and the second one was acquired after. A total of 70 deep-seated landslides occurred during this event between 2 and 5 September 2011. This study shows that the SLBL method is efficient using either the slope deformations identifiable on the DEM before the release of the landslide or a reliable 2.5-D failure surface created by using both DEMs (the 2.5-D corresponds to a surface which has only one z value for each x – y coordinate; in other words, no true vertical topography or overhang can be represented perfectly). In addition, this method allows for the reconstruction of eroded deposits and buried valleys. Most of the volumes estimated are within ±35 % of the estimation made by Chigira et al. (2013), and the coefficients of expansion range from 10 % to 25 %. These results show considerable sensitivity to the parameters used for the reconstruction of the landslide volume estimations and demonstrate the need for an efficient and fast tool to reconstruct potential landslide geometries or histories. [ABSTRACT FROM AUTHOR]

Landslides are a main cause of human and economic losses worldwide. For this reason, landslide hazard assessment and the capacity to predict this phenomenon have been topics of great interest within the scientific community for the implementation of early warning systems. Although several models have been proposed to forecast shallow landslides triggered by rainfall, few models have incorporated geotechnical factors into a complete hydrological model of a basin that can simulate the storage and movement of rainwater through the soil profile. These basin and full hydrological models have adopted a physically based approach. This paper develops a conceptual and physically based model called open and distributed hydrological simulation and landslides-SHIA_Landslide ( Simulación HIdrológica Abierta, or SHIA, in Spanish)-that is supported by geotechnical and hydrological features occurring on a basin-wide scale in tropical and mountainous terrains. SHIA_Landslide is an original and significant contribution that offers a new perspective with which to analyse shallow landslide processes by incorporating a comprehensive distributed hydrological tank model that includes water storage in the soil coupled with a classical analysis of infinite slope stability under saturated conditions. SHIA_Landslide can be distinguished by the following: (i) its capacity to capture surface topography and effects concerning the subsurface flow; (ii) its use of digital terrain model (DTM) to establish the relationships among cells, geomorphological parameters, slope angle, direction, etc.; (iii) its continuous simulation of rainfall data over long periods and event simulations of specific storms; (iv) its consideration of the effects of horizontal and vertical flow; and (vi) its inclusion of a hydrologically complete water process that allows for hydrological calibration. SHIA_Landslide can be combined with real-time rainfall data and implemented in early warning systems. [ABSTRACT FROM AUTHOR]

An experiment has been carried out to find a reliable method to map 3D geological contacts using high-resolution Digital Elevation Models (DEMs) and pictures. Various airborne and ground-based photos, and a classical geological map, have been draped by several users on DEMs of the Scex Rouge Mountain (Vaud, Swiss Alps) producing several 3D textured models of the relief. On each of these photorealistic models, geological contacts were then drawn as polylines by hand. The locations of resulting polylines have been then compared. The draping procedure, actually the choice of pairs of control points used for the texturing step, appears to be the main source of discrepancies between the results of the different models. The subjectivity of users in drawing polylines is of lesser importance. We observed also that the widely accepted geological map of the area does not provide an accurate representation of the local geology in steep areas, especially near-vertical rock faces where this effect is marked. Even if high quality and high-resolution data are becoming increasingly more available, a robust way to map geological structures directly in 3D is still lacking. In addition, there is a crucial lack of tools, with editing capabilities able to handle large point cloud datasets and gigapixel images. Finally, the methodology described in this Technical Note is intended to be useful for modelling simple geological structures, such as cylindrical folds, in a complex environment comprising near-vertical rock faces. [ABSTRACT FROM AUTHOR]

The present study analyses the spatial pattern of quaternary gravitational slope deformations (GSD) and historical/present-day instabilities (HPI) inventoried in the Swiss Rhone Valley. The main objective is to test if these events are clustered (spatial attraction) or randomly distributed (spatial independency). Moreover, analogies with the cluster behaviour of earthquakes inventoried in the same area were examined. The Ripley's K-function was applied to measure and test for randomness. This indicator allows describing the spatial pattern of a point process at increasing distance values. To account for the non-constant intensity of the geological phenomena, a modification of the K-function for inhomogeneous point processes was adopted. The specific goal is to explore the spatial attraction (i.e. cluster behaviour) among landslide events and between gravitational slope deformations and earthquakes. To discover if the two classes of instabilities (GSD and HPI) are spatially independently distributed, the cross K-function was computed. The results show that all the geological events under study are spatially clustered at a well-defined distance range. GSD and HPI show a similar pattern distribution with clusters in the range 0.75-9 km. The cross K-function reveals an attraction between the two classes of instabilities in the range 0-4 km confirming that HPI are more prone to occur within large-scale slope deformations. The K-function computed for GSD and earthquakes indicates that both present a cluster tendency in the range 0-10 km, suggesting that earthquakes could represent a potential predisposing factor which could influence the GSD distribution. [ABSTRACT FROM AUTHOR]

Numerous 3D rockfall simulation models use coarse gridded digital terrain model (DTM raster) as their topography input. Artificial surface roughness is often added to overcome the loss of details that occurs during the gridding process. Together with the use of sensitive energy damping parameters, they provide great freedom to the user at the expense of the objectivity of the method. To quantify and limit the range of such artificial values, we developed an impact-detection algorithm that can be used to extract the perceived surface roughness from detailed terrain samples in relation to the size of the impacting rocks. The algorithm can also be combined with a rebound model to perform rockfall simulations directly on detailed 3D point clouds. The abilities of the algorithm are demonstrated by objectively extracting different perceived surface roughnesses from detailed terrain samples and by simulating rockfalls on detailed terrain models as proof of concept. The results produced are also compared to that of rockfall simulation software CRSP 4, RocFall 8 and Rockyfor3D 5.2.15 as validation. Although differences were observed, the validation shows that the algorithm can produce similar results. With the presented approach not being limited to coarse terrain models, the need for adding artificial terrain roughness or for adjusting sensitive damping parameters on a per-site basis is reduced, thereby limiting the related biases and subjectivity. [ABSTRACT FROM AUTHOR]

Rockfall, rock avalanches, and other hazards are driven by discontinuities that can lead to a problem. In order to identify and calculate the potential risk associated with these discontinuities, it is necessary to know the volume of the unstable material and the potential reach when it collapses. The following two routines were created in Matlab to facilitate these calculations.If the discontinuities are planes like faults, bedding, and other structural features, a body can be isolated, and its volume can be calculated. Planos aims to help the researcher to display the planes mapped on the field and to display their relation to the topography. The user needs to have the position of planes on the topography, the dip, and the dip direction. This can be found on the field during the campaign, on a geological map, or using a high-resolution digital model (Lidar or Photogrammetry). Finally, Planos requires the digital elevation model (DEM) of the study zone. The planes are prolongated to have the same extent as the DEM, and the section of the topography will be delimited by those planes. Planos closes the body between planes and creates a mesh with the nodes of each plane underneath the topography and the DEM. This allows the application to calculate the volume and to create a new elevation model minus this volume. Today, expensive and complicated software allows the user to upload the digital elevation model (DEM), to create the planes and to estimate the volume. This procedure takes time and requires a certain knowledge to perform. Planos was created to make these functions accessible and to simplify the procedure. In our recent research on landslide propagation, the propagation models were performed with DAN3D (Hungr and McDougall 2009). This software uses ascii grid files (.grd) to work and exports a text file with the characteristic of each particle in the space. Constructing the grid can be time consuming and complicated. If the user performs multiple models, it is also a long process to compare all of them in order to find the best fit. Finally, the user must create rendering. PrePostDAN3D aims to replace complicated software and to accelerate the pre and post treatment. First, the user needs to have the topography, and the source in ascii files (.asc). The program helps the user to choose the correct parameters from a database (McKinnon 2010), and creates a sensitivity analysis table. After DAN3D processing, the program compares the numerical models and the data collected on the field and looks for the minimum difference between the same parameters. Finally, the user can select the model that they consider to be most conform to reality and visualise the result in 2D or 3D. PrePostDAN3D looks for a simple way to accelerate the procedure for propagation modelling. [ABSTRACT FROM AUTHOR]