Integration of remote sensing data and GIS for accurate mapping of flooded area

This paper gives a synergetic use of satellite radar images and ancillary information to detect flooded areas at the peak time and evaluates its potential with the mapping. The procedure was tested on the catastrophic flood occurred in Regione Piemonte (Italy) in November 1994. Two ERS-1 SAR images were processed, one acquired one month before the flood and the other one acquired three days after the event. Visual interpretation and two different thresholding techniques were performed. The derived flooded maps shows only a small fraction (20%) of the actually flooded lands because of the time delay between the flood peak and the satellite passage. To overcome this limitation, the authors developed a new procedure to estimate the flooded area at the peak time by integrating the flooded area from SAR imagery with the digital topographic data by a GIS technique. This method allowed inundated areas covering 96.7% of the flooded area officially recorded by the local government to be mapped. The proposed procedure is suitable for mapping flooded areas even when satellite data are acquired some days after the inundation, thus overcoming the constraint of the temporal resolution in the application of SAR in hydrology.