Delineation of 1993 Midwest flooding using ERS-1 SAR, SPOT and Landsat imagery

Multi sensor active and passive optical band imagery offer distinct advantages over single sensor imagery in the assessment of flooded areas, but the interpretation must consider weather and river flow conditions. Nadir-looking panchromatic (black and white) imagery from SPOT (10-m spatial resolution) and multiband Landsat (30-m spatial) radiometers was used. The reflectance brightness of surface water in contrast to surrounding vegetation and soil at visible and near IR optical wavelengths allowed delineation of flooded areas. Variations around the nominal water brightness level were encountered from material modulation caused by (1) the turbulence of water flowing in constricted channel reaches and behind bridges and (2) the amount of sediment in the flood waters. Clouds block surface reflectance at optical wavelengths from those sensors, whereas active sensing SAR acquires imagery under all weather conditions. Side-looking active C-band ERS-1 SAR imagery (12.5-m spatial resolution) was also used. The backscatter component from smooth flooded regions was minimal relative to the rough surfaces from surrounding land forms which allowed delineation of flooded areas. The backscatter from flooded regions was modulated when the surface was roughened by (1) surface winds and (2) turbulent flow. These conditions change the backscatter enough that the brightness from the water surface exceeds that from the land surface. The above multisensor information from both optical and microwave imagery (C-band SAR) is used in delineating the flooded regions over St. Charles, MO during July 1993