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STATUS OF FLOOD MONITORING WITH MULTISENSOR REMOTE SENSING
A. Zilahy, S. Herath, K. Musiake
Ph.D. Candidate, Professor, Professor
University €
* Tokyo, Institute of Industrial Science, Laboratory for Hydrology and Water Resources Engineering
7-22-1 Roppongi, Minato-ku, Tokyo 106-8558, Japan
Commission VII, Working Group 2
KEY WORDS: Flood Monitoring, Multisensor Remote Sensing, Multitemporal Remote Sensing.
ABSTRACT
During floods, the assessment of flooded areas is
transportation systems, or by other unfavorable con
planning of emergency relief and repairs to commun
flood risk maps. Flood monitoring and the detection o
of flow routing and flood forecasting on a catchment scale. By t
severely restrict the use of aircraft, and extensive clou
operating at optical wavelength. The synthetic aperture r
tool for flood mapping. In this paper, the multisensor appro
sensors — in case of flood assessment is discussed. In most app
taken by optical sensors
radar platforms) are analyzed in a suitable comp
Depending on the methods used, different c
inundated areas are usually underestimated, main
make, because ground truth measurements are often missing. Another
above the flooded area. With the advent of new satellites, which can cover the Earth more frequently,
to measure hydrological parameters, space technology can be used for flood assessment and for moni
often restricted by bad weather, by the interruption of telecommunication and/or
ditions. The assessment of inundated areas is required quickly (a) to enable the
ications, transportation and other services and (b) for the production of river
f water bodies are important also for coupling the data to hydrological models
heir nature, most floods occur in bad weather conditions, which can
d cover precludes the use of most earth observing satellites, which rely on
adar (SAR) can penetrate clouds and darkness, and therefore it is an efficient
ach of remote sensing — the analysis of images obtained by different
lications, the initial conditions are mapped with high-resolution images
(Landsat, SPOT, etc.), and during the flood event, the available images (from meteorological, optical or
uter software system, often combined with a geographical information system (GIS).
lassifications with varying results can be prepared. Different analysis show that the
ly because of insufficient image-resolution, but proper comparisons are difficult to
difficulty in the analysis is the infrequent overpass of satellites
and sensors designed directly
toring other natural phenomena
more often, more accurately and hopefully operationally around the globe.
INTRODUCTION
During the past decades, huge amount of data had been
collected by remote sensing satellites orbiting the Earth. The
first Earth-observing satellite, the Landsat-1 was launched 26
years ago, in 1972, and with this a new chapter started in
measuring natural phenomena on Planet Earth. In the past two
decades, numerous satellites had been launched, equipped with
different sensors for monitoring a wide range of atmospheric,
hydrologic, geologic and other parameters. Some of the newer
satellites carry active microwave sensors as well, which is a
very promising tool for different monitoring tasks, especially
above sites with significant cloud cover during the monitoring
periods. Active microwave sensors (or radars) can penetrate
clouds, darkness, fog, haze or light rainfall. With satellite
remote sensing huge areas can be observed at once, which is
necessary for the study of global or regional natural phenomena
and environmental problems. Depending on the spatial
resolution of the image, local scale monitoring is also possible,
but it is less frequently used in flood monitoring. Data from
satellite remote sensing has been used operationally in several
fields of science, e.g. meteorology and atmospheric sciences.
On the other hand, land applications often need more research,
as in the case of soil moisture retrieval, because of limited
knowledge on the interaction of land surface (or atmosphere)
and electromagnetic waves.
FLOOD MONITORING
Monitoring the inundated areas from space gives additional
information to in situ observations, which are often restricted by
bad weather, by the interruption of telecommunication and
transportation systems, or by other unfavorable conditions.
Flood monitoring has different applications in the field of
hydrology. The mapping of inundated areas and analyzing the
changes of their extent during a flood event gives information
on the individual flood event, which is strongly dependent on
catchment characteristics, weather conditions before, during and
after the event, land use patterns and other catchment
characteristics. In the case of flash floods, when a sudden and
abundant rainfall causes the flooding, it is difficult to give flood
warning, and therefore the mitigation process is limited. Still,
near real-time monitoring can help determining the moving
waterfront, thus helping the emergency relief processes.
For disaster mitigation, simply monitoring the flood event may
not be sufficient. For mitigation purposes, hydrological models
are often used to simulate and forecast river discharges with
input data including rainfall as the most important. Until. the
present time, accurate measurement of rainfall distribution on a
catchment scale makes much of the difficulties, besides the
problems of measuring vegetation distribution, soil type
distribution and other factors. More information is needed on
several parameters like the preceding meteorological and
hydrological state throughout the catchment, historical data on
flood events in the past and the weather condition before, during
and after the past events, the topography of the region, land use
patterns and changes in the land use, etc. When hydrological
models validated to individual catchments are used to forecast
flooding from rainfall measurements, satellite remote sensing
can help in this process by updating some of the input
parameters of the simulation models, like the extent of
inundated areas.
Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 779
