Flood and discharge monitoring during the 2008 Iowa flood using AMSR-E data

The objective of this work is to demonstrate the potential of passive microwave data in monitoring flood and discharge conditions. The study case is the recent flood in Iowa in summer 2008. AMSR-E 37 GHz data have been used to calculate a Polarization Ratio Variation Index (PRVI). This new index uses the classic Polarization Ratio Index along with its mean and standard deviation to detect anomalies in soil moisture and/or flooded area extent. The PRVI have been used to delineate inundated areas in Iowa. Then surface area of inundated regions has been compared with downstream discharge observations. A rating curve has been developed to assess the relationship between the extent of flooded area and discharge magnitude downstream. A time lag term has been introduced to account for the delay between water surface extent and stream flow. Time lag values showed that this parameter is a good proxy for watershed drainage time and time of concentration (i.e. the flood wave propagation time plus the longest runoff time in the watershed.) suggesting that passive microwave image can be use to measure key watershed hydrologic parameters.