New perspectives in monitoring water resources in large tropical transboundary basins based on remote sensing and radar altimetry.
Résumé
The combined use of remote sensing and radar altimetry is offering entirely new perspectives for the monitoring of water resources in large tropical trans-boundary basins. Based on a study conducted mostly in the region of the Llanos de Mojos, a large complex of wetlands located within the southernmost extension of the Amazon Basin, at the Brazilian border with Bolivia and Peru, but also based on previous studies, we give some results that will illustrate this point of view. First, the results are showing the current limitations of the radar altimetric missions, which were designed primarily for ocean level or ice caps studies: essentially the revisit time, the size of the water bodies that can be monitored, and the lack of reliable data in presence of relief. Nevertheless, they also show that the data processing and the tools we developed to select appropriately the data, allow retrieving quite accurately the seasonal variability of the water elevation within the basin selected. Second, we are stating the absolute necessity of coupling these data with remote sensing images, in order to retrieve useful information on the hydrologic behaviour of this very complex system. The common altitudinal reference of the radar altimetry missions is opening new modelling opportunities, as the river slope is a key parameter for hydrodynamical studies. Last, the spatial distribution reachable nowadays, and the perspectives offered by the future sensors, are going forward a global, detailed capability of monitoring wetlands and floodplains, as well as their relationship with the river flow. The applications resulting from these monitoring tools are of primarily importance for tropical poorly gauged basins, and we will review as a conclusion some of them, as infrastructure monitoring and planning, flood and drought monitoring and forecast, fluvial waterway monitoring and transport planning, fluvial dynamics of the riverbed and discharge modelling.