Retrieval of bare soil and vegetation parameters from wind scatterometer measurements over three different climatic regions

Medium to low resolution (1-50 km) active microwave sensors such as spaceborne scatterometers and wide-swath mode synthetic aperture radars have great potential as tools for long term monitoring over land and ice. To optimise the use of this kind of data, the heterogeneity of the target and its effects on the radar measurements need to be investigated and modelled, particularly in the view of retrieving geophysical parameters. In this paper, wind scatterometer measurements over three different test sites, the NOPEX region in Sweden, the HAPEX-Sahel site in Niger and the Niger delta area in Nigeria, are analysed. For these regions, a forward model is developed by considering the backscatter contributions of the bare surface, the seasonal and evergreen vegetation and the open water areas. Colocated high spatial resolution SAR data and ground information are used to characterise the target scene. The model is then inverted to retrieve monthly soil roughness, dielectric properties and vegetation parameters. It is shown that the measurements contain enough information to characterise these three different regions and to monitor their temporal evolution. The retrieved values obtained for the bare surface and the vegetation parameters are consistent with ground measurements collected in these areas. Further improvements are achieved by incorporating the time scale variability of the variables investigated into the retrieval scheme.