Identification of flooded areas with ERS-1 SAR imagery (Walloon Region) (-)

Start-End  - 
Programme TELSAT 2
Contract TELSAT/II/610
Objective In recent years, the Walloon region has been plagued by floods due to extremely high water levels after heavy or prolonged rainfall. To be able to cope with these problems, the service for hydrological studies (SETHY) of the Walloon region decided in 1993 to establish a GIS, allowing the prediction of high water levels and identification of risk zones for flooding.

Since radar sensors such as ERS-1 SAR are an appropriate tool for detecting (and quantifying) humidity in the surface soil, and since the acquisition of radar images is not hampered by cloud cover, it was suggested to integrate radar images in the GIS.

Purpose of the study : to evaluate the use of ERS-1 SAR images (acquisition between December and April, in a 3 day cycle) for the identification and monitoring of risk zones for flooding in the winter.
Method - Selection of 2 images : one scene taken on the day of the flooding, the other scene taken just before or after (3-6 days) the flooding. Standard pre-processing of the radar images. Superposition of 2 images. Calculation of a difference image; on this resulting image, the pixel values corresponding to the highest differences (higher than a threshold) are selected as nuclei of flooding.
- Validation of the results by a field campaign and on the basis of the ‘map of flooding’ of 1984 (MET).
- Software used for image processing : ERDAS
Result - The use of ERS-1 SAR images allows production and updating of a ‘map of risk zones’ for flooding. Modifications due to newly constructed dikes or other infrastructure works can be detected. The updated risk map can be used to elaborate and update maps indicating zones suitable for construction (residential areas, housing, …). It is also feasible to create a dynamic image of the risk of flooding in relation to the high water level.
- A map of flooded areas can be produced in real-time, the day of the flooding (acquisition of the radar scene and image processing included). The probability of acquiring at least one ERS-1 SAR scene during a flooding is 80% for the valley of the Lesse.
- The methodology is simple to implement and is operator independent. SETHY intends to integrate this methodology in the general hydrological information system CARHY of the Walloon region.
As a result of this study, the research group is now participating in the European FLOODAWARE project.
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Team
Project Leader: DAUTREBANDE Sylvia ULg - Gembloux Agro-Bio Tech - Echanges Eau-Sol-Plante
Location Hydrographic basins of the Ourthe and Amblève Rivers (Belgium)
Hydrographic basins of the Lesse River (Belgium)
Sensors used AMI SAR
Applications Hydrology & freshwater resources
Natural hazards & disasters
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Datasets used