IMAGE CHANGE DETECTION ON URBAN AREA: THE EARTHQUAKE CASE
G. Bitelli®, R. Camassi °, L. Gusella *”, A. Mognol *
a DISTART, University of Bologna, Viale Risorgimento, 2, 40136 Bologna, Italy -
(gabriele.bitelli, luca.gusella, alessandro.mognol)@mail.ing.unibo.it
b INGV, Via Donato Creti, 12 - 40128 Bologna, Italy - camassi@bo.ingv.it
KEY WORDS: Remote Sensing, Earthquakes, Change Detection, Disaster, Multitemporal
ABSTRACT:
Earthquakes constitute one of the most relevant natural hazards on wide areas, involving both economical and social aspects. In the
last years, lots of resources have been involved in developing methods for a quick response management and for mapping
macroseismic damage information of urban estate; macroseismic data are especially critical either for social and scientific aspects.
Turkey's Marmara earthquake in 1999 demonstrated that seismologic community doesn't have sufficient resources, organization and
procedures to completely classify the damage on widely damaged urban areas. Thanks to the new documentation possibilities
offered for instance by digital image acquisition and visual reality scenery georeferenced by GPS, a wide variety of techniques can
be used in loci to help post survey damage assessment and macroseismic evaluation, but in the most relevant earthquakes, such as
the Marmara's one, these surveys are not sufficient to take all the information, due to time and resources limits.
In this sense, image remote sensing techniques could play an important role to quickly detect damage distribution, also before
starting of rescue operation, and therefore supplying a view of earthquake effects.
Various techniques of data processing are useful to enhance dama
resolution data leads to new possibilities in the integration of
information extraction from Medium Resolution to Very High
ge information, and furthermore the increasing availability of high-
field survey with remote sensing. This work presents results in
Resolution satellite imagery both for rapid damage assessment
purpose and damage information extraction, using classical and object-oriented approaches. In particular, object oriented approach is
useful to integrate different images, because is less affected by registration problems, and the improved space of states of the object
could improve classification accuracy than probabilistic method. Cases of study presented are Marmara (1999) and Boumerdes
(2003) earthquakes, where geometrical registration and radiometrical enhancement problems are faced up.
These experimental studies are leading to the opportunity, in the future, to integrate classical damage survey and image oriented
semi-automatic interpretation.
1. INTRODUCTION
1.1 Macroseismic damage assessment by field surveys:
collecting data, intensity scale.
Strong earthquakes require extensive and immediate field
investigation to record damage patterns. The observations of
damage level and distribution after a destructive earthquake are
of primary importance for planning the first rescue activities
and for understanding the effect of shaking on buildings.
Macroseismic observations require qualified personnel
(preferably multi-disciplinary: seismologists, geologists, civil
engineers, etc.) and for scientific purposes the macroseismic
data must be collected quickly, in the immediate aftermath of
the earthquake, before the cleaning and reconstruction process
has started. Otherwise the data get lost and cannot be
reconstructed.
Engineering-based field survey teams do not necessarily gather
the data that are of most interest to seismology: the engineers
are mainly interested in severe failures and damage assessment
to decide if a building should be used, restored or demolished:
the macroseismologist is interested to the overall damage
distribution, including the borderline between slight damage
and no damage, and the spatial patterns of variation in intensity
caused by local conditions. Sometime, an isolated small
damage to an old structure could be much more important to
this end rather that an extensive, uniform collapse of RC
buildings.
This is the main reason to perform macroseismic surveys after
damaging events, but the old fashioned approach based on
written descriptions accompanied by some pictures is not
anymore sufficient. The traditional damage survey must be
accompanied by more quantitative data able to support also
future re-interpretation.
[n recent times intensity maps are based on safety survey forms
(Thywissen and Boatwright, 1998) but can take advantage also
of modern technologies using telephone interviews (Dengler
and Dewey, 1998) or Internet polls (Wald et al., 1999). Direct
field surveys remains however the primary source of
information to assess the damage distribution.
Intensity maps are produced using different intensity scales like
MCS (Mercalli-Cancani-Sieberg), MSK (Medvedev-
Sponheuer-Karnik) and EMS-98 (European Macroseismic
Scale) in Europe and Mediterranean region.
The revised version of the European Macroseismic Scale based
on the MSK scale, provided with a detailed handbook
(Grünthal, 1998), tries to define accurately some key terms, like
building type, damage grade and quantity. The EMS-98 scale is
a very modern scale, which needs a lot of detailed information
on buildings types and vulnerability classes, on damage grades
and its percentage distribution among the total number of
structures interested by the earthquakes (Table 1).
Some new techniques has been recently used to collect
additional data, useful for understanding the reason of some
building failures (HVSR, Horizontal to Vertical Spectral Ratio
measurements) or to provide to other seismologists
uninterpreted visual material (with the QTVR, QuickTime
Virtual Reality technique) for intensity assessment (Mucciarelli
et al., 2001).
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