- Infrastructural monitoring to ensure an
undisturbed supply of aid.
Satellite remote sensing techniques can be used for the
reduction of natural disasters if these techniques enable
us to collect data about atmospheric conditions and/or the
characteristics of the earth's surface which may lead to
the occurrence of processes which may bring information
about natural disasters or can help us to take actions
which reduce the disastrous effects of these processes.
2. CHARACTERISTICS OF SATELLITE REMOTE SEN-
SING AND GIS
Remote sensing data derived from satellites are excellent
tools for the mapping of the spatial distribution of
disaster-related data within a relatively short period of
time. Today many satellite-based systems exist, with
different characteristics related to their:
- Spatial resolution: the size of the area on the terrain
that is covered by the instantaneous field of view of a
detector.
- Temporal resolution: the revisit time of the satellite for
the same part of the earth surface.
- Spectral resolution: the number and width of the
spectral bands recorded.
The most frequently used systems are given in Table 1.
ped with two sensor systems, covering adjacent paths
each one with a 60 kilometres swath width. The sensors
have an off-nadir looking capability, offering the possibility
for images with good stereoscopic vision. The option for
sidewards looking results also in a higher temporal reso-
lution. SPOT is sensing the terrain in a panchromatic
band and in three narrower spectral bands (green, red
and infrared). The spatial resolution in the panchromatic
mode is 10 meters, while the three spectral bands have a
spatial resolution of 20 meters. The system lacks spectral
bands in the middle and far (thermal) infrared.
Radar satellite images, available from the European ERS-
1 and the Japanese JERS, are offering an all-weather
capability, since the system is cloud penetrating. Theore-
tically this type of images can yield detailed information
on surface roughness and micromorphology. However,
the wavelengths and looking angles applied until now
have not been very appropriate for the application in
mountainous terrain. The first results of the research with
radar interferometry are very promising and indicating
that detailed terrain models to an accuracy of around one
meter or less can be generated, which creates the possi-
bility to monitor slight movements related to landslides,
fault displacements or bulging of volcanic structures.
Remote sensing data should generally be linked or cali-
brated with other types of data, derived from conventional
mapping, measurement networks or sampling points to
derive at parameters which are useful in the study of
disasters. The linkage is done in two ways, either by vi-
Table 1 Specifications of some frequently used multispectral remote sensing products.
Parameter Landsat Landsat SPOT
MSS TM XS PAN
Number of 4 7 3 1
spectral bands
Spectral resolution 0.5 -1.1 um 0.45 - 2.35 um 0.5 - 0.9 uum 0.5 - 0.7 um
10.4 - 12.5 um
Spatial resolution 80m 30 m 20m 10m
120 m in TIR
Swath widh 185 km 185 km 2 x 60 km 2 x 60 km
Stereo no no yes yes
Temporal resolution 18 days 18 days 26 days 26 days
5 days off nadir 5 days off nadir
Besides the use of conventional aerial photographs,
which often remain the most useful tools in many types of
disaster studies, the application of satellite data has in-
creased enormously over the last decades. After the
initial low-spatial resolution images of Landsat MSS (60m
x 80m), Landsat is also offering Thematic Mapper images
with a spatial resolution of 30 meters (except for the
thermal infrared band) and an excellent spectral resoluti-
on with 6 bands covering the whole visible and the near
and middle infrared part of the spectrum and with one
band in the thermal infrared. Landsat has an overpass
every eighteen days. Despite this theoretical temporal
resolution, weather conditions are a serious limiting factor
in this respect, since clouds are hampering the acquisiti-
on of data of the ground.
The weakest point of the Landsat System is the lack of an
adequate stereovision. Theoretically a stereomate of an
TM image can be produced with the help of a good digital
terrain model (DTM), but this remains a poor compensati-
on as long as very detailed DTMs are not currently
available. The French SPOT satellite, however, is equip-
40
sual interpretation of the image or via classification.
A very powerful tool in the combination of the different
types of data required for disaster management are geo-
graphic information systems. A geographic information
system (GIS) is defined as a "powerful set of tools for
collecting, storing, retrieving at will, transforming and
displaying spatial data from the real world for a particular
set of purposes" [2].
The first experimental computerised GISs were develo-
ped as early as the nineteen sixties, but the real boom
came in the eighties, with the increasing availability of
"cheap" (personal) computers. It is estimated that by
1986 more than 4000 different systems had been develo-
ped around the world [2]. Many different GIS systems
exist today, with different characteristics with regards to
the type of data structure (vector versus raster), data
compression techniques (quadtrees, run-length coding),
two-dimensional versus three-dimensional data storage,
mainframe, mini-, and microcomputer hardware, and user
interfaces (pop-up menus, mouse-driven, help options,
etc.).
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B6. Vienna 1996
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