Flooded area estimation using radar images and digital elevation model

In this study were evaluated the utility of ERS-1 satellite imagery in conjunction with ancillary data for mapping the flooded areas of the November 1994 flood event occurred in Northern Italy. Two images were analyzed, one collected a month before the flood and the other one collected three day after the inundation. Two processing procedures and a visual interpretation were applied within a masked area extracted from the digital elevation model (DEM). Areal extent of flooded surfaces retrieved by the different methods were compared with the actual flood extension derived from field survey. Intermediate results showed that only a small fraction of the total inundated area was possible to estimated because of the time shift between flood and satellite passage. To overcome this limitation a procedure based on the integration of flooded areas as previously estimated by radar images, with a cost matrix calculated on the basis of the DEM was developed in a Geographical Information System (GIS) environment. This method allowed to map additional inundated areas amounting 96.7% of the actual flooded area. Result shows that even if radar data are taken some days after the inundation, they are still well suited to reconstruct flooded area when DEM is employed in the mapping process.