MONITORING OF GEOLOGICAL SITES BY LASER SCANNING TECHNIQUES
M. Scaioni*, A. Giussani*, F. Roncoroni”, M. Sgrenzaroli”, G. Vassena*
? Politecnico di Milano — Polo Regionale di Lecco, Dept. L.LA.R., via M. d'Oggiono 18/a, 23900 Lecco, Italy
e-mail: (marco.scaioni; alberto.giussani; fabio.roncoroni}@polimi.it
? Topotek — Inn. Tec. srl, via Branze 38, 25123 Brescia, Italy — e-mail: sgrenzaroli@topotek.it
* Università degli Studi di Brescia — Dept. of Civil Engineering, via Branze 38, 25123 Brescia, Italy
e-mail: vassena@ing.unibs.it
Commission VII, Working Group 5
KEY WORDS: Laser Scanning, Landslides, Geology, Monitoring, Visualization, DEM/DTM
ABSTRACT:
In the last 5 years terrestrial laser scanning (TLS) technology has shown very large improvements, either in the instrumental aspects
and in softwares for data processing and visualization. While first applications concerned only the architectural or in general the
close-range field due to the small operating range, nowadays dealing with large scenarios is possible as well. New “long-range” TLS
are really suitable to be applied in geological and glaciological surveying and monitoring, representing a very interesting issue for
the Italian (and not only) research and social community, due to the mountain character of a large portion of its land.
[n the paper some guidelines for executing a survey of a landslide by means of TLS techniques are addressed; problems such as 3D-
view registration, survey planning, data processing and information extraction are concerned. Furthermore, two application in this
field carried out by a research group made up of Politecnico di Milano and the University of Brescia are presented. Geological
application concerns the survey of a slope threatening a par
know marble quarry of Botticino (Brescia).
1. INTRODUCTION
Geological instability is one of the most serious problem
affecting the Italian country, resulting in a large amount of
economic damages and, very often, in the lost of human lives.
From North to South of the country, several areas present some
geological and morphological characteristics which make them
really prone to slope disaster. This nature has been getting
worse and worse because of a bad mountain land management,
which did not prevent from destruction of forests and the
continuous growth of human settlements. On the other hand,
monitoring and prevention of geological disasters has been
widely ignored, with the only exceptions of cases attracting the
attention of mass-media. Furthermore, the changeable
behaviour of climate in the latest years has resulted in a further
increment of the problem.
However, in the recent years many efforts have been carried out
in order to prevent landslides, involving either research insitutes
and public administrations. An important impulse to this has
been given by the introduction of some new monitoring and
surveying methods, which have substituted or integrated
traditional approaches and instruments of geology and
topography. Concerning topographic and photogrammetric
techniques, new sensors have been applied to geometric survey
of slopes, integrating the use of automatic total station, digital
photogrammetry (aerial and terrestrial) and GPS techniques.
Preminently, these new approaches are dominated by terrestrial
laser scanning techniques (TLS) and by ground based
inteferometric SAR analysis (Rudolf et al., 1999). Both methods
are able to survey the object in a manner that is not more
limited to the measurement of a selected number of control
points, such as in traditional methods, but resulting in the
acquisition of the whole surface in a short time. Thank to a TLS
is now possible to acquire a dense point-cloud describing the
3D surface of a landslides with a cm accuracy, referred to a
t of the village of Caslino d'Erba, near the Lake of Como, and the well-
given reference system. Terrestrial /nSAR techniques allow the
determination of relative displacements at different times with
an accuracy of few mm.
At the current state-of-the-art, the application of laser scanning
techniques seems to be — in the opinion of the authors — the
widespread real possibility of surveying a whole slope surface,
because of the availability of different commercial TLS models
and of SWs for data management and processing. InSAR
methods are still in development and are limited to a small
number of experimental applications.
For the sake of completeness, among new methods for ground
movement detection and monitoring, satellite InSAR tecniques
based on point scatterers extraction (see Ferretti et al., 2001)
cannot be forgotten. Interesting applications are currently
carried on in the Italian Alpine area based on this kind of
analysis, which tries to localize those sites featuring anomalous
vertical displacements, to be further investigated by terrestrial
methods.
Moreover, laser scanning allows to derive some topographic
products that some years ago cannot be. A part from a
topographic description of the slope, carried out through the
extraction of horizontal and vertical sections, a dense DSM of it
can be acquired; this can be used in modelling geological
problems (prevision of the movement of a slope, preferable path
of fall in case of rolling rocks and the like).
The TLS data can be easily integrated to those taken by other
kinds of sensors, such as typical geological investigation
instruments, geophisical analyses, photogrammetric and
topographic surveys. The 3D point-cloud, once it is registered
to a given reference system, could be thought as the geometric
framework for representing all different kinds of data used for
the landslide monitoring, so that all information could be
managed in a unique environment.
The paper will describe firstly some general aspects concerning
TLS survey for geological applications. Then, two practical
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