Satellite-Based Estimates of River Runoff
S. Grünler, SG; R. Romeiser, RoRo; D. Stammer, DS
Institute of Oceanography, University of Hamburg

Global quantitative estimation of river runoff is important in a broad range of applications, such as water management, meteorology, oceanography, and climate modeling. Global temporal and spatial assessments of river discharge are, however, highly uncertain, mainly because of the sparse coverage of in-situ measurements in developing countries. Recent advances in satellite-based remote sensing technology can contribute to overcoming this lack of spatial information on river volume transport. One promising technique is the use of spaceborne synthetic aperture radar along-track interferometry (ATI) for measuring surface currents at high spatial resolution. For the first time the German satellite TerraSAR-X, which was launched in June 2007, will permit repeated ATI measurements at selected test sites during a period of several years. The results presented here originate from the research project "Analyses on the usability of upcoming satellite data for the remote sensing of river runoff" (AnaNAF), carried out at the University of Hamburg and funded by the German Research Foundation. We give an overview of the project and of some first results. Within AnaNAF we will evaluate the potential of satellite measurements of various parameters with different sampling characteristics (e.g. current measurements by ATI and water level measurements by radar altimetry) to develop an optimal data synthesis system for river discharge estimates and to assess the achievable accuracy of such estimates for different local flow conditions. To evaluate various possible measuring strategies, high-resolution flow data in the Elbe river (Germany) from a numerical model of the Federal Waterways Engineering and Research Institute are used as input for comprehensive simulations. For example, runoff estimates on the basis of measured surface current fields and river widths are simulated. These parameters are related by the Manning equation, and surface currents and river widths can be retrieved directly from TerraSAR-X ATI imagery. Our results indicate that some of the considered measuring strategies would provide quite realistic estimates of the Elbe river runoff dynamics. Further investigations consider the relevance of this finding to various major rivers around the world.


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