Using satellite altimetry and historical gauge data for validation of the hydrological significance of the JERS-1 SAR (GRFM) mosaics in central Africa

As part of the Global Rain Forest Mapping (GRFM) project, two 100 meter resolution, continental-scale JERS-1 L-band SAR mosaics have been generated over the Congo river basin in central Africa. The satellite acquisitions were scheduled to coincide with the high and low water marks of the Congo river, in order to facilitate assessment of the spatial and temporal distribution of the annual flooding patterns in the river basin. With L-band microwave signals being particularly sensitive to inundated vegetation, the GRFM mosaics were expected to provide an opportunity to investigate inundation dynamics in the poorly mapped wetlands in central Africa. This paper provides an assessment of how well the two central African GRFM mosaics actually represent the two extreme flooding conditions in the Congo basin. In the absence of operational river gauge stations along the Congo, river stages derived by the NASA Radar Altimeter on TOPEX/POSEIDON were used to validate the water level variations during 1996, when the GRFM acquisitions were performed. Historical gauge data dating back to 1959 and earlier, were used to provide an indication the general flooding cycles in areas which could not be measured by the altimeter. Also affecting the "hydrological usefulness" of the mosaics, the temporal composition of the JERS-1 data used to form the two canvases, i.e. the occurrence of gaps or scenes with deviating acquisition dates, was finally also investigated.