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Spatial data, used in GIS, is data with a geographic com-
ponent, such as maps, aerial photography, satellite ima-
gery, and rainfall data, borehole data etc. Many of these
data will have a different projection and coordinate sy-
stem, and need to be brought to a common map basis, in
order to superimpose them. GIS allows for the combinati-
on of these different kinds of spatial data, with non-spatial
attribute data, and use them as input data in complex
models. One of the main advantages of the use of the
powerful combination techniques of a GIS, is the evalua-
tion of several scenarios, and the analysis of the sensiti-
vity of the models by varying some of the input data.
3. CHARACTERISTICS OF GEOLOGICAL NATURAL
DISASTER TYPES AND THE ROLE OF REMOTE SEN-
SING
Widely known are the potentials of applications of data
from satellites to predict weather-related disastrous phe-
nomena such as extreme storms and rainfall. This paper
is concentrating on geology-related natural disasters. As
these disaster types are concerned with natural pheno-
mena with wide variations in characteristics, size, speed
of development, etc., the following paragraphs will con-
centrate separately on the role of satellite remote sensing
in the reduction of the following three types of geological
hazards: earthquakes, volcanic eruptions, and landslides.
3.1 Earthquakes
The area affected by earthquakes are generally large (in
the order of 102 - 104 km?), but they are restricted to well-
known regions (e.g. plate contacts). Typical recurrence
periods vary from decades to centuries. Observable as-
sociated features include fault rupture, damage due to
ground shaking, liquifaction, landslides, fires and floods.
The following aspects play an important role: distance
from active faults, geological structure, soil types, depth
of the water table, topography, and construction types of
buildings.
In the phase of disaster prevention satellite remote sen-
sing can play an important role in the mapping of active
faults, using neotectonic studies using Landsat TM/SPOT
or radar, and in the measurement of fault displacements,
using satellite Laser Ranging (SLR), Global Positioning
System (GPS), or radar interferometry. So far the most
important data for seismic hazard zonation is derived
from seismic networks. In seismic microzonation, the use
of satellite remote sensing is very limited, since the data
is derived from accelerometers, geotechnical mapping,
groundwater modelling, and topographic modelling at
large scales. Earthquakes cannot be predicted with the
current state of knowledge, and therefore also satellite
remote sensing cannot play a role in the phase of
earthquake disaster preparedness. In the phase of
disaster relief, they can only play a role in the identificati-
on of large associated features (such as landslides).
Structural damage to buildings cannot be observed with
the poor resolution of the current spaceborne scanning or
radar systems.
3.2 Volcanic Eruptions
The areas affected by volcanic eruptions are generally
small (« 100 km?), and restricted to well-known regions.
The distribution of volcanos is also well known, however,
41
due to missing or very limited historical records, the dis-
tribution of active volcanos is not (especially in developing
countries). Many volcanic areas are densely populated.
Volcanic eruptions can lead to a large diversity of
processes, such as explosion (Krakatau, Mount St. He-
lens), pyroclastic flow (Mt. Pelee, Pinatubo), lahars
(Nevado del Ruiz, Pinatubo), lava flows (Hawai, Etna),
and ashfall (Pinatubo, El Chincon). V Volcanic ash clouds
can be distributed over large areas, and may have consi-
derable implications for air-traffic and weather conditions.
Satellite remote sensing can be used in the phase of
disaster preparedness for the distribution and type map-
ping of the of volcanic deposits using Landsat TM, SPOT,
or Radar. For the determination of the eruptive history
other types of data are required, such as morphological
analysis, tephra chronology, and lithological composition.
Volcanic eruptions occur within minutes to hours, but are
mostly preceded by clear precursors, such as fumarolic
activity, seismic tremors, and surface deformation
(bulging). The thermal band of Landsat TM can be used
to monitor the thermal characteristics of a volcano, and
radar interferometry in the measurement of surface de-
formation. NOAA-AVHRR data can be used to monitor
lava flows or ash plumes. Meteosat, GOES or TOMS
(Nimbus-7) can be used to monitor the extent of volcanic
ash clouds and the SO» content.
Using SIR-C/X-SAR multi-frequency two-pass interfero-
metric radar imagery Lanari et al. (1996) [7] performed a
(non classical) textural analysis by estimating fractal fBm
parameters over Mount Etna. Furthermore, fractal analy-
sis proved that the pivoting median filter strongly reduces
the high frequency artifacts that affect interferometric
SAR DEMs, and, on the other hand, makes geological
features definitively more apparent. This analysis also
showed that the multi-frequency fusion of SAR data pre-
serves all the geological content. In their trailblazing pa-
per the authors state that future developments of the
proposed technique for the generation of multi-frequency,
two-pass interferometric SAR DEMs combined with the-
matic information promise an extremly high potential for
volcanic disaster issues.
3.3 Landslides and Other Mass Movements
Individual landslides are generally small (0.001 - 1 km?),
but they are very frequent in certain mountain regions.
Landslides occur in a large variety, depending on the type
of movement (slide, flow, fall), the speed of movement
(mm/year - m/sec), the material involved (rock, soil), and
the triggering mechanism (earthquake, rainfall, human
interaction).
In the phase of disaster prevention satellite imagery with
sufficient spatial resolution and stereo capability (SPOT)
can be used to make an inventory of the past landslides,
and to collect data on the relevant parameters involved
(soils, geology, slope, geomorphology, landuse, hydrolo-
gy, rainfall, faults etc.) In the phase of disaster prepared-
ness use could be made of the same systems applied for
the prediction of floods (see Section 3.1). Monitoring of
displacements of large landslides can be performed with
radar interferometry. The assessment of damage using
satellites is only possible if the spatial distribution is very
high, or if the individual landslides are large.
An important interpretation element for both lithological
and structural analysis of SAR with respect to mass mo-
vements is the drainage pattern. In general, the geomor-
phological detail and the synoptic view of a density of a
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B6. Vienna 1996
