International Archives of Photogrammetry andRemote Sensing. Vol. XXXII Part 7C2, UNISPACE HI, Vienna, 1999
99
I5PR5
UNISPACE III - ISPRS/EARSeL Workshop on
“Remote Sensing for the Detection, Monitoring
and Mitigation of Natural Disasters”
2:30-5:30 pm, 22 July 1999, VIC Room B
Vienna, Austria
NATURAL HAZARDS OF GEOLOGIC ORIGIN-
EROSION, LAND DEGRADATION/DESERTIFICATION, VOLCANOES AND ACTIVE FAULTS-
THE UNESCO/IUGS GEOLOGICAL APPLICATION OF REMOTE SENSING (GARS)- PROGRAMME
Dietrich Bannert and Robert Missotten
Unesco/IUGS GARS-Programme
ABSTRACT
Geological natural hazards have become a significant threat to a large part of the world population. Remote sensing methods can be
used to assess the potential for many natural and man made geological hazards. The Geological Application of Remote Sensing
(GARS) Programis addressing a wide variety of these issues in order to have more powerful tools developed to assess potential
hazards, to monitor ongoing geological catastrophes and to register and appraise the damages occurred.
1. INTRODUCTION
In recent years natural hazards - many of those of geologic origin
- became an issue of increasing public awareness. There are a
number of reasons, governing this development:
larger populations moving into potential risk areas
unsuitable land-use and land management
loss of financial investments due to natural catastrophes
rapid dissemination of news, intensive media coverage
There is, a on the other hand, a rapid development in the
information technology sector, especially in earth observation.
Earth observation satellites and remote sensing aircraft are the
platforms, which are used to install sophisticated equipment
designed to scan the earth in numerous wavelengths of the
electromagnetic spectrum. The data acquired is mainly in digital
format. Multispectral scanners (MSS) with bands numbering
from 3 to 220, covering the visible to short-wave range of the
electromagnetic spectrum are the most conunon instruments in
space and on aircraft. The trend to improve the spatial resolution
will continue and add unprecedented image data, which, when
combined with selected MSS bands, will build a powerful source
of information. Radar satellites with their all-weather capabilities
add to the spectrum of satellites. Radar data together with the
precise ranging of the satellite will add measured quantities to
earth observation (MASSONET, D. 1999). For the first time we
are in a position to generate an exact topographical model of the
earth surface. Altitudes can thus be compared from continent to
continent. Future missions will deliver data for a higher vertical
resolution and will be of a more precise cartographic quality'.
Powerful computers are available practical for everyone and
expectations are high that automated procedures will be
developed that warn authorities and organisations of disasters to
come.
2. EROSION, LAND
DEGRADATION/DESERTIFICATION
In geology we identify two major forces that influence the surface
of our planet. They are the endogene forces and the exogene
forces. Both can result in disasters. The endogene forces,
stemming from the earth interior, can cause uplifting,
earthquakes, as well as volcanic activity. Among the exogene
forces are erosion, flooding, desertification with all the
associated disasters once larger populations are affected.
All the processes mentioned here can develop into catastropliic
events in the case, the population is not prepared. Often the event
was underestimated, or the event developed more rapidly than
anticipated.
2.1 Erosion
Erosion and sedimentation are two processes, which are generally
everywhere present on the land surface. Wind and water remove
the topmost surface and the material will be deposited elsewhere.
Geologists call the deposition of material sedimentation. Both
processes can achieve catastrophic dimensions. Landslides strike
without warning and laliars, a form of volcanic sedimentation,
can bury within hours whole valleys under meters of sediments.
2.2 Land-degradation
Land-degradation can lead to a permanent desertification. Arable
land is going out of production. This process is the result of a
large number of different factors: overpopulation induces the
degradation of the natural vegetation, which in return leads to a
liigher susceptibility to desertification. But drought lias an even
more adverse impact. The distribution of rainfall spatially as well
as timely can have disastrous effects on vulnerable environments.
1972-1973 the Sahelian drought, brought the affected countries
south of the Sahara desert almost to a collapse. Vegetation
monitoring on a day by day basis is a powerful tool when it is
combined with data on population, soil capabilities, rainfall etc.
For more detailed observation a large technical potential lies in
the application of hyperspectral data to vegetation studies.
