Evaluation of JERS-1 SAR mosaics for hydrological applications in the Congo river basin

Two JERS-1 Synthetic Aperture Radar (SAR) mosaics covering central Africa were investigated with respect to their potential usefulness for studies of seasonal flooding dynamics in the Congo river basin. The mosaic quality was initially evaluated with respect to geometric and radiometric accuracy, as well as to the temporal composition of the data used in the mosaic assembly. The investigation revealed no major defects that should prevent utilization of the data for hydrological applications. The state of flooding captured in each of the two mosaics-preferably portraying the Congo and its tributaries during their annual maximum and minimum water marks-was furthermore evaluated by examining river stage information. Stage data contemporary with the satellite acquisitions (1996) were derived from the TOPEX/POSEIDON Radar Altimeter and supplemented by historical in situ records. The results suggest that the SAR mosaics may serve well to appraise the maximum extents of flooding in the Congo river basin, but quite poorly to assess the dynamics and ranges of the variations. It was reckoned that a minimum of three acquisitions within 1 year would be required to better describe the complex hydrology in the region. The validation uncertainty in rivers where only historical in situ data were available was evident, thus stressing the utility and future potential of radar altimetry to provide substitute measurements of river stages.