Influence of flood conditions and vegetation status on the radar backscatter of wetland ecosystems

The aim of this paper is to assess the use of RADARSAT SAR data for wetland ecosystem identification considering the influence of target features (vegetation type, flood conditions, phenology; and fires), as well as sensor parameters (varying incidence angles). The Lower Delta islands of the Parana River in Argentina were selected as the study area. Six SAR images acquired during the summer and winter of 1997 and 1998 were used This set includes Standard Beams S1, S4 and S6 to account for the incidence angle effect. Radar backscatter of samples taken at known sites was analyzed. The forest backscatter signal shows temporal stability during summer and winter, either with leaf-on or leaf-off trees. On the contrary; backscattering from forest is strongly enhanced by underlying water: Radar returns were found to change from an attenuated signal to one dominated by double-bounce behaviour. In wetlands dominated by rushes, the dominant interaction mechanism may change from double-bounce to specular reflection due to flood. During normal water-level conditions, the ability to differentiate forest from herbaceous vegetation was found to decrease with increasing incidence angle. Under extreme flooding, radar backscattering decreases from steep to shallow incidence angles, about 3 dB for forest, and 4 dB for rushes.