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.