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

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