Flood area detection from multipass Synthetic Aperture Radar (SAR) data can
be performed via amplitude change detection techniques. These methods allo
w flooded zones to be discriminated only when they are flooded at the time
of the second passage, and not at the time of the first one. Coherence deri
ved from multipass SAR interferometry can be used instead, as an indicator
of changes in the electromagnetic scattering behaviour of the surface, thus
potentially revealing all the areas affected by the flood event at any tim
e between the two passes. The paper presents a prototype application of suc
h techniques, that is, a flood map obtained from ERS-1/2 data taken over Be
ziers (Southern France), through proper thresholding of a combination of am
plitude and coherence information. Produced in the framework of an ESA proj
ect, the map consists of a DXF vector file which can be imported directly i
nto most commercial GIS software.