Flood mapping inferred from remote sensing data

In ungauged basin, space-based information is essential for the monitoring of hydrological water cycle, in particular in regions undergoing large flood events where satellite data may be used as input to hydrodynamic models. A method for near 3D flood monitoring has been developed which uses synergies between radar altimetry and high temporal resolution multi-spectral satellite. Surface Reflectance from the MODIS Terra instrument are used to map areas of open water as well as aquatic vegetation on a weekly basis, while water level variations in the inundated areas are provided by the radar altimetry from the Topex / Poseidon (T/P) and Envisat satellites. We present this synergistic approach to three different regions: Niger Inner delta and Lake Tchad in Africa, and Ganga river delta in Asia. Based mainly on visible and Near Infra Red (NIR) imagery is suitable to the observation of inundation extent. This method is well adapted for arid and semi arid regions, but less for equatorial or boreal ones due to cloud coverage. This work emphasizes the limitations of current remote sensing techniques for full 3Ddescription of water storage variability in ungauged basins, and provides a good introduction to the need and the potential use of the future SWOT (Surface Water and Ocean Topography) satellite mission