The proposed approach is based on the Polarization Ratio index (PR), which is computed using AMSR-E 37 GHz, vertically and horizontally polarized brightness temperature values. The Water Surface Fraction (WSF), which represents the fraction of flooded soil, was derived on a pixel-per-pixel basis will also be considered. The ability of the passive microwave signal to penetrate clouds and its sensitivity to the amount of water at the near soil surface gave it a unique potential in flood monitoring and soil moisture estimation. The potential of the polarization ratio and polarization difference in mapping flooded areas have been tested by numerous researchers. The use of polarization ratio, instead of difference, reduces the effect of the atmosphere as well as the signal dependency to the effective soil temperature. The observed PR index is a combination of different responses generated by the permanent open water surface, flooded area, non-flooded area and soil moisture. All these surface types were weighted differently by using their corresponding surface fractions. Therefore, the observed PR can be written, for each pixel, as a linear combination of the contributions of these different fractions.
Simulations have been carried out using recent AMSR-E images taken from late March 2008 to the end of June 2008. The mixing model provided maps of flooded and non-flooded areas. The Iowa flood of June 8, 2008 involved most of the rivers in eastern Iowa
The preliminary results have showed that high flood fractions in central Iowa coincide with the recorded major flooding in the same period in Iowa. An agreement has also been found between the microwave image results and flooded fractions sensed by visible images (MODIS). The generated flood maps are in the process to be compared to the spatial distribution of the registered precipitation over the study area. Rating curves will be later developed and used to establish am AMSR-E based regional flood warning system.
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