Margherita Fiani

Monitoring of large landslides by Terrestrial Laser Scanning techniques: field data collection and processing

Abstract We have monitored a large landslide that causes extensive damage by using Terrestrial Laser Scanners (TLS) and Global Positioning System (GPS) receivers. Our surveys have confirmed that the slope undergoes a continuous change. When using TLS some operational difficulties arise. We have used different TLSs types to better evaluate the reliability of our surveys; a full wave TLS has allowed to make easier the data filtering. All surveys have been framed in the same absolute reference system; this has been done by connecting both targets and laser stations to a Global Navigation Satellite System (GNSS) Permanent Reference Stations network. A direct comparison among the DEMs allows to infer the movements of the landslide.

Landslide monitoring using multitemporal terrestrial laser scanning for ground displacement analysis

In the analysis of the temporal evolution of landslides and of related hydrogeological hazards, terrestrial laser scanning (TLS) seems to be a very suitable technique for morphological description and displacement analysis. In this note we present some procedures designed to solve specific issues related to monitoring. A particular attention has been devoted to data georeferencing, both during survey campaigns and while performing statistical data analysis. The proper interpolation algorithm for digital elevation model generation has been chosen taking into account the features of the landslide morphology and of the acquired datasets. For a detailed analysis of the different dynamics of the hillslope, we identified some areas with homogeneous behaviour applying in a geographic information system (GIS) environment a sort of rough segmentation to the grid obtained by differentiating two surfaces. This approach has allowed a clear identification of ground deformations, obtaining detailed quantitative information on surficial displacements. These procedures have been applied to a case study on a large landslide of about 10 hectares, located in Italy, which recently has severely damaged the national railway line. Landslide displacements have been monitored with TLS surveying for three years, from February 2010 to June 2012. Here we report the comparison results between the first and the last survey.

Uncertainty in Terrestrial Laser Scanner Surveys of Landslides

Terrestrial laser scanning (TLS) is a relatively new, versatile, and efficient technology for landslide monitoring. The evaluation of uncertainty of the surveyed data is not trivial because the final accuracy of the point position is unknown. An a priori evaluation of the accuracy of the observed points can be made based on both the footprint size and of the resolution, as well as in terms of effective instantaneous field of view (EIFOV). Such evaluations are surely helpful for a good survey design, but the further operations, such as cloud co-registration, georeferencing and editing, digital elevation model (DEM) creation, and so on, cause uncertainty which is difficult to evaluate. An assessment of the quality of the survey can be made evaluating the goodness of fit between the georeferenced point cloud and the terrain model built using it. In this article, we have considered a typical survey of a landsliding slope. We have presented an a priori quantitative assessment and we eventually analyzed how good the comparison is of the computed point cloud to the actual ground points. We have used the method of cross-validation to eventually suggest the use of a robust parameter for estimating the reliability of the fitting procedure. This statistic can be considered for comparing methods and parameters used to interpolate the DEM. Using kriging allows one to account for the spatial distribution of the data (including the typical anisotropy of the survey of a slope) and to obtain a map of the uncertainties over the height of the grid nodes. This map can be used to compute the estimated error over the DEM-derived quantities, and also represents an “objective” definition of the area of the survey that can be trusted for further use.

Multi-temporal Terrestrial Laser Scanning Survey of a Landslide

Terrestrial laser scanning (TLS) has proven to be a very effective technique for landslides monitoring, even if some critical issues exist for providing highly reliable results. This chapter presents the methodology adopted in performing four surveys, carried out over three years on a large slump landslide in order to get effectively comparable data. The first problem concerns the setting up of the reference system, which has been realized by means of global navigation satellite system permanent stations ETRF00 datum. This solution was able to maximize the stability over time even at the expense of a slightly lower precision, which was, however, in the order of 1–2 cm with data recorded during the whole duration of TLS survey. An assessment of geo-referencing accuracy was carried out with respect to the only stable artifact present in the landslide area. This check pointed out that in the central part of the point cloud the repeatability between different surveys was slightly greater than 5 cm. To ensure the quality of the obtained multitemporal digital terrain models (DTM’s) over the entire region of interest, the choice of the interpolation algorithm has been performed and verified with a cross-validation method on the basis of a sample extracted from the data set. To detect the kinematics of the landslide in its several parts, both the DTM’s and profiles have been used, which have proven to be particularly useful for the interpretation of details. After the localization of various landslide bodies (keeping into account slope and aspect maps derived from the DTM), the evaluation of the volumes mobilized over time has been carried out by differencing the DTM’s. This analysis has been separately carried out in the different parts on which the landslide bodies had been subdivided.

Assessment of DEM derived from very high-resolution stereo satellite imagery for geomorphometric analysis

ABSTRACT Very high-resolution satellite stereo images play an important role in cartographical and geomorphological applications, provided that all the processing steps follow strict procedures and the result of each step is carefully assessed. We outline a general process for assessing a reliable analysis of terrain morphometry starting from a GeoEye-1 stereo-pair acquired on an area with different morphological features. The key steps were critically analyzed to evaluate the uncertainty of the results. A number of maps of morphometric features were extracted from the digital elevation models in order to characterize a landslide; on the basis of the contour line and feature maps, we were able to accurately delimit the boundaries of the various landslide bodies.

Terrestrial laser scanner for the analysis of airport pavement geometry

Abstract The knowledge of the geometric features of an airport’s pavement surface is essential to ensuring the safety and comfort of the driving users. For this purpose, it is important to find the most suitable survey methods and computation procedures for determining these geometric features and their evolution over time. In this study, we used a terrestrial laser scanner (TLS) to survey a stretch of a taxiway of an international airport. We designed the survey with the goal of defining the optimal parameters for the scans and the spacing between the TLS station points, combining high efficiency with data quality and accuracy. An algorithm for the semi-automatic extraction of the longitudinal and transversal profiles of the track from the digital elevation model (DEM) has been implemented. Longitudinal and cross slopes have been computed from the profiles using a linear fit, assessing the conformity of the values to the standards. The algorithm allows the verification of irregularities and the assessment of the severity of deviations from a linear trend. Our approach is suitable for obtaining an accurate reconstruction of the road surface that can be measured in post-processing and that is geo-referenced in a way that allows monitoring over time. We believe that the surveying technique that we analysed and assessed could improves the effectiveness of the measurements, and it could be used wherever pavement geometry control cannot be performed on discrete elements but rather a continuous approach is needed.

Use of DEMs Derived from TLS and HRSI Data for Landslide Feature Recognition

This paper addresses the problems arising from the use of data acquired with two different remote sensing techniques—high-resolution satellite imagery (HRSI) and terrestrial laser scanning (TLS)—for the extraction of digital elevation models (DEMs) used in the geomorphological analysis and recognition of landslides, taking into account the uncertainties associated with DEM production. In order to obtain a georeferenced and edited point cloud, the two data sets require quite different processes, which are more complex for satellite images than for TLS data. The differences between the two processes are highlighted. The point clouds are interpolated on a DEM with a 1 m grid size using kriging. Starting from these DEMs, a number of contour, slope, and aspect maps are extracted, together with their associated uncertainty maps. Comparative analysis of selected landslide features drawn from the two data sources allows recognition and classification of hierarchical and multiscale landslide components. Taking into account the uncertainty related to the map enables areas to be located for which one data source was able to give more reliable results than another. Our case study is located in Southern Italy, in an area known for active landslides.

Use of Terrestrial Laser Scanner for Rigid Airport Pavement Management

The evaluation of the structural efficiency of airport infrastructures is a complex task. Faulting is one of the most important indicators of rigid pavement performance. The aim of our study is to provide a new method for faulting detection and computation on jointed concrete pavements. Nowadays, the assessment of faulting is performed with the use of laborious and time-consuming measurements that strongly hinder aircraft traffic. We proposed a field procedure for Terrestrial Laser Scanner data acquisition and a computation flow chart in order to identify and quantify the fault size at each joint of apron slabs. The total point cloud has been used to compute the least square plane fitting those points. The best-fit plane for each slab has been computed too. The attitude of each slab plane with respect to both the adjacent ones and the apron reference plane has been determined by the normal vectors to the surfaces. Faulting has been evaluated as the difference in elevation between the slab planes along chosen sections. For a more accurate evaluation of the faulting value, we have then considered a few strips of data covering rectangular areas of different sizes across the joints. The accuracy of the estimated quantities has been computed too.

Digital images in support of historical building data bases

The study of complex monuments is highly interdisciplinary, requiring input from surveyors, architects, archaeologists, historians, geotechnical and structural engineers, etc.