- Bangladesh lies almost entirely on the delta of three major rivers: the Padma (the
Ganges), the Jamuna (the Brahmaputra), and the Meghna. A considerable portion of
Bangladesh has been repeatedly devastated by floods associated with cyclonic storm
surges along its coastal islands and riverine flooding along the rivers traversing the lowlying
deltaic plain. Extensive flooding is a recurring event affecting a significant
proportion of the population.
The International Council of Scientific Unions (ICSU), through the International
Geographical Union (IGU) is providing scientific support to the Bangladesh Flood
Action Plan as part of the United Nation's International Decade for Natural Disaster
Reduction (IDNDR). The IGU study has focused on a long term survey of flood prone
areas using remote sensing, geographic information systems (GIS), and the global
positioning system (GPS). RADARSAT imagery serves to improve the imagery base for
the area, as Synthetic Aperture Radar (SAR) imagery of terraces and levees in natural
areas nearly covered by seasonal floods have better discrimination of elevated land
surfaces than many other imagery sources. RADARSAT provides an "all-weather"
remote sensing tool for monitoring flood events. In this study, the imagery is being used
to determine areas affected by annual and catastrophic floods, specifically isolated
villages in the flooded areas.
A protocol using the application of "low pass" smoothing filters to the
RADARSAT data, followed by defined digital number thresholds to select regions of
interest allows for the identification of villages in the imagery. After further testing of
the chosen threshold ranges combined with ground truthing in Bangladesh, this protocol
would be suitable for emergency management use during flooding. Isolated villages
needing assistance during a flood event would be identified and prioritized accordingly.
The day/night and cloud-penetration characteristics of radar may be the only
practical means of mapping the extent of monsoonal flooding of the deltaic plain, where a
large rural population is forced to adapt to seasonal isolation in a flooded landscape.
Maps of rural hamlets and isolated flood refuge sites will never keep pace with the
growing population and constantly changing fluvial landscape without the use of high
altitude remote sensing satellites such as RADARSAT.
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