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

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

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

ABSTRACTVery 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

APPLICATION OF LIDAR-DERIVED DEM FOR DETECTION OF MASS MOVEMENTS ON A LANDSLIDE

In order to reliably detect changes in the surficial morphology of a landslide, measurements performed at the different epochs being compared have to comply with certain characteristics such as allowing the reconstruction of the surface from acquired points and a resolution sufficiently high to provide a proper description of details. Terrestrial Laser Scanning survey enables to acquire large amounts of data and therefore potentially allows knowing even small details of a landslide. By appropriate additional field measurements, point clouds can be referenced to a common reference system with high accuracy, so that scans effectively share the same system. In this note we present the monitoring of a large landslide by two surveys carried out two years apart from each other. The adopted reference frame consists of a network of GNSS (Global Navigation Satellite Systems) permanent stations that constitutes a system of controlled stability over time. Knowledge of the shape of the surface comes from the generation of a DEM (Digital Elevation Model). Some algorithms are compared and the analysis is performed by means of the evaluation of some statistical parameters using cross-validation. In general, evaluation of mass displacements occurred between two surveys is possible differencing the corresponding DEMs, but then arises the need to distinguish the different behaviors of the various landslide bodies that could be present among the slope. Here landslide bodies’ identification has been carried out considering geomorphological criteria, making also use of DEM derived products, such as contour maps, slope and aspect maps

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

The role of ephemeris and GPSs distribution in high resolution satellite images modeling.

The geometric resolution of the images coming from the new generation satellites is almost competitive with that found in the traditional aerial photograms. The aim of this work is to define the role of satellite ephemerides and to optimise the number andvdistribution of Ground Control Points (GCPs) for the image registration. A zone of the Campania region in Italy has been used as a test area: it is characterized by a mountainous area without constructions and by flat land areas densely inhabited. The images that have been used relate to different epochs and different satellites such as Spot5, Ikonos2 and QuickBird. Spot5 images have also been used to generate automatic Digital Elevation Models (DEMs). The assessment of DEM precision has been carried out by comparison with raster DEMs from cartography. The GCPs coordinates have been obtained from a GPS network made up of almost hundred and some of them are used as Check Points (CPs). Different tests have been performed, either varying the number of GCPs or hypothesizing the presence or absence of satellite ephemeris. Some numerical evaluations confirm that the use of the satellite ephemeris greatly reduces the amount of residuals on the CPs; in the case of Spot5 images this improvement becomes even more evident

Using the Data Fusion tecnique for producing tematic maps.

The University of Salerno (Italy) has recently been equipped with a pair of aerials that are able to receive data transmitted from various satellite platforms such as the NOAA and the Terra-1 and Aqua-1 EOS. These satellites are fitted with sensors that pick up information regarding soil and cloud temperature, the humidity level of the atmosphere, the presence of extraneous water, the presence of certain substances such as chlorophyll, the surface colour of the ocean and the presence of plankton with a spatial resolution that at its greatest reaches 250 m. Great use is therefore made of a vast amount of data that concerns our geographical area which allows for a fairly approximate assessment of the state of health (desertification, deforestation, abundance of surface water) and the potential risks (landslides, fires, plant and crop infections or diseases) to which the territory is prone. Nevertheless, the data is supplied with differing precision to the ground and with different pixel dimensions, therefore it is not possible to generate, taking as a starting point the data alone, (thematic map) which, besides furnishing qualitative information, also supplies correct and precise metric information. By using the Data Fusion technique it is possible to project the data supplied by various sensors onto a higher resolution image in order to obtain a representation that allows for a synthesis of all available information