Flood extent depiction by physical downscaling of flooded fraction estimates from microwave remote sensing

A physical downscaling algorithm for flood mapping is described with validation test results from two flood events. The algorithm is capable of producing 3-arcsecond resolution flood maps globally from lower-resolution (e.g., 27-km) flooded fraction estimates such as those derived from microwave remote sensing. The algorithm is based on an analysis of topography, stream networks, and permanent open water cover that results in a measure of grid point floodability relative to the other points within a microwave measurement footprint. Test results with simultaneous flood maps from higher-resolution imagery show that the downscaled flood maps correspond spatially to observed flood extent. Correct typing rate (relative to imagery) is 85% when flooded fraction inputs are error free and 64% when microwave-derived flooded fraction inputs are used.