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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
METHODOLOGY FOR LANDSLIDE MONITORING IN A ROAD CUT BY MEANS OF
TERRESTRIAL LASER-SCANNING TECHNIQUES
M.A. Hernandez®, J.L. Pérez-Garcia®, T. Fernandez’, F.J. Cardenal’, E. Mata®, A. López, J. Delgado", A. Mozas'
? Dept. of Cartographic and Geodetic Engineering and Photogrammetry, Campus de las Lagunillas, Ed. Tecnología e
Ingeniería, University of Jaén, 23071 Jaén (acaro, jlperez, tfernan, jcardena, emata, alarenas, jdelgado,
antmozas)@ujaen.es
VIII/1: Disaster Management
KEY WORDS: displacements measurement, landslide, road cut, terrestrial laser-scanning.
ABSTRACT:
After the heavy rains of 2009/10 winter, a road cut in the national highway A-44 and the upper slope became unstable; the mass
invaded the way and caused important traffic interruptions by several months. The landslide was measured by means of terrestrial
laser-scanner techniques and, because of the zone morphology, the used methodology involved scanning the mobilized zone from
different stations with several captures from each point. Two scanning campaigns were carried out in a time interval of 14 days. The
antenna phase centers were determined by GPS techniques and incorporated to the point clouds as an additional point in the TLS
reference system; next, the relative orientation of the different point clouds of each scan station is made, adjusting and merging them
in a single point cloud; finally, we proceed to data transformation to a reference system global and common to both campaigns, in
which surface and terrain models can be compared. From field data, a digital surface model have been built, and then filtered and
edited to have digital elevation models of centimeter spatial resolution. The results obtained by the comparison of models show two
rupture zones in the road cut affecting also to the upslope, in which an important volume material flowed with superficial
displacements of about 0,55-0,65 m day . We also calculated 210 m? of depleted material and 124,5 m? of accumulated material; the
differences between these volumes (wasting material) are explained because the civil works that were made to clear the road of
materials.
1. INTRODUCTION level to manage TLS data, but many times these software are
not enough and a global automatic processing of these data are
Landslides are one of the most widespread earth surface hazards, ^ not yet possible.
causing hundred of human victims and billions of dollars in
damages per year. One of the goods more affected by slope However, the most important issue is the correct georeferencing
movements are lineal works (highways and roads, railways, etc.) ^ of TLS data that must be carried out in a unique and stable
where processes such as falls of weathered block, slides or flow reference system. Uncertainty in the system definition and in the
of materials on the road produces traffic and other problems in adjustment and orientation of the different point clouds will
these infrastructures. These movements are sometimes ^ make the results are not accurate and the useful. There are
unpredictable, although slope instability methods help us to several methodologies available to georeferencing TLS point
resolve certain unstable areas. In this case the determination of ^ clouds used to terrain deformation monitoring; this approaches
the geometry of the unstable area is capital to resolve that are different depending on TLS instrument, involved distances,
problem, because of that it is necessary the improvement of ^ number and distribution of measurement stations, terrain
geomatic tools to capture, define and analyze that geometry in characteristics (morphology, stability, visibility, accessibility ...)
an accurate way. and the data processing software.
In the last years, different geomatic techniques from data The reference system (global or local) can be defined in
acquisition (optical remote sensing, photogrammetry, radar, different ways. The first of them is the use of targets (circular
LiDAR, GPS, surveying ...) to data processing (especially GIS) planes, cylindrical and spherical) placed on stable or unstable
are being used to landslide characterisation, monitoring and zones of the studied terrain and measured by a GPS or total
analysis. Among them, terrestrial laser scanner (TLS) is station (Miller, 2008, Cardenal et al., 2008; Bu & Zhang, 2008)
becoming one of the most used to deformation monitoring to define an internal system. Other option, used in multi-
because it gives a high density and spatial accuracy data in a temporal analysis, requires the inclusion of stable zones in the
short time interval (Abellán et al, 2006; Abellán et al., 2009; different campaigns to define the reference system common to
Montserrat & Crosetto, 2008, Monserrat et al., 2008; Lichun et ^ all of them (Montserrat & Crosetto, 2008; Travelleti et al, 2008).
al, 2009). In this way, natural and man-made slopes can be
captured with a high reliability and speed in comparison with A third way is the data georeferencing using the position of the
other measurement techniques not based in images different scan stations; this position can be measured with
(conventional surveying and GPS). accuracy by GPS. It will be necessary to measure at least three
well distributed stations (not located in the same straight line) to
However, there are some difficulties in TLS data processing transform the local reference system of the scanner to a
related with the management of large amount of data, the geo- common and global system. Pesci et al. (2007a y 2007b)
referencing and adjustment of TLS data and the requirement of employs this procedure to deformation monitoring in the
data filtering and classifications. The management of TLS are — Vesuvio volcano. In this case, the scanned terrain and scan
carried out by means of several commercial applications of high stations not have to be in stable zones.
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