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2. THE CONCEIVING OF THE EVALUATION
SYSTEM FOR DAMAGES RESULTING FROM
NATURAL DISASTER
In order to define natural disaster affected areas, in a first
stage a high accuracy isn't required and it can be done within a
GIS, using high resolution remote sensing or low scale aerial
photograms. On this occasion, affected perimeters,
departmental connections, implications on adjacent regions
and environment can be defined and based on global analysis
of these data; decisions can be made concerning the prevention
of environmental implications and of damage extension, as
well as quick response means.
At this level of information, the method described by
(Khyihar A. and Winkler G.,1993) is recommended, these
method based on volume elements depending on the spatial
resolution of basic data, can be used for the urban space
analysis, the basis data maybe collected by photogrammetry
Or remote sensing.
After a first emergency response, the problem of disaster
damages accurate evaluation occurs. These can be measured
and evaluated using the comparison of 3D reference model
built before the catastrophe using classical analytical
photogrammetry (Griln A.,1996) or digital photogrammetry
technology through automatic or semi-automatic processing of
aerial photograms, information completed (for buildings
facades) with digital or digitized terrestrial photograms and
the 3D model built after the catastrophe using quick response
means (helicopters equipped with high space resolution video
cameras). The changes detected between the two 3D
models must be analyzed within 3D informational systems
(SIT 3D). Not all the damages can be detected at this level
using these systems which are based on the information
collected from the aerial photograms combined with terrestrial
photograms and high space resolution video images only great
proportion collapses can be detected: balconies, roof parts etc.
A detailed damage analysis (interior wall cracks, sliding,
buildings ' internal structures’ demolition) can be done only
within a reference 3D Technical Informational System (SITh
3D) (Weindorf M. and adders, 1997) built for each and every
construction and must stand for a basis for disaster damage
evaluation. At the first two levels and the 3D model, the
photogrammetry and remote sensing are the principal source of
information for collecting basic data, in order to create the
geometrical data base.
In the present paper, the concept and the way of achieving the
geometrical basis for the reference model by using gathered
data through photogrammetrical methods are described, the
collected data being perfected with the information obtained
through large scale topographical maps digitization. The post
disaster 3D model is created by exploiting high resolution
video images. The changes detection is achieved by
comparison and the analysis of notable changes between the
two models.
3. THE CREATION OF MODELS CORRESPONDING
TO THE THREE STEPS
The informational contents corresponding to the three steps is
very different and so are the processing data. This thing
together with the way of practical development in case of
natural disasters has led to organizing the three intervention
steps and the organizing system and financial administration
of data.
3.1 The creation of the model according to the satellite
images
According to the first level of natural disasters analysis, for
specifying the affected areas and studying their effects and
their impact upon the environment, the satellite images of
high resolution can be used, which as show (Fritz W.. L.,
1996) and (Konecny G., 1996) could be received in real time
in the near future. The satellite images of high spatial
resolution will be of much help if they are in real time, in the
possible case of introducing a world system of observing and
monitoring natural disaster, proposed by ( Kuroda T. and
Koizumi S., 1991) and whose use is required badly by
natural disaster and the damages produced by them,
frequently enough in different geographic area of the Earth.
The ERDAS software system has been used in order to
process the remote sensing images and to realize the GIS
system.
The technology of detecting the changes by using satellite
images is already known. Significant changes can be
emphasized on this base by using the following methods:
by comparing the multitemporal images given by the some
receiver, by the multitemporal images regression or by filed
classified multitemporal images comparison. Corresponding
to the first method mentioned and consequent to the
preliminary processing of the two multitemporal set of data
their differences were computed. An image plan containing
polygons in which the most notable changes are expected are
created for negative and positive differences. It is in the
interior of these polygons that it must be intervened for first
aid of limiting the damages and preventing extension to
adjacent areas.
The determination of changes can be achieved not only
through the analyze of multitemporal images differences or
through the analyze of their arrangements, but also through
statistical analysis on 3D systems of a set of models resulted
from repeated measurements in order to determine the trend
of changes as well as the disaster temporal deviations, as for
terrain sliding or fires.
Data collected during several periods is imposed in certain
situations and a 3D model is automatically imposed. In this
situation the results can not be located only on a single map.
Data statistic description and their visual description is a
possibility which doesn't help to establish local trends and
temporal variations. The statistic description generalizes and
simplifies the multitemporal data, reducing their possibility of
utilization (Schlagen D.J. and Newton C.M.,1996). A mention
should be made: that the efficiency of this step is limited by
the speed with which satellite data reaches the user.
3.2 The creation of 3D model before and after
disaster
The disasters damages evaluation stage concerning affected
areas defined inthe first stage is based on the 3D model
conceived before and after the disaster. The pre-disaster
model 3D, fig.], must be conceived for the whole urban
area that could be affected by a natural disaster.
In order to build a 3D model representing the reference
situation corresponding to the pre- disaster situation, a SIT
3D inserted model, analytical photogrammetry typical
methods can be used, method tested by authors like (Grün A.
and others,1996) or (Zavoianu and others, 1997). Digital
photogrammetry ^ using scanned or digital ( aerial and
Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 763
