首页|Understanding geophysical sources of uncertainty of satellite interferometric discharge estimation using manning's approach: A case study of gbm delta.
Understanding geophysical sources of uncertainty of satellite interferometric discharge estimation using manning's approach: A case study of gbm delta.
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Like most river deltas, Bangladesh represents a geographically small region with numerous criss-crossing rivers. The total number of rivers in Bangladesh exceeds 300 of which, 57 rivers are transboundary. Given the widespread unavailability of flow data across the entire river basins of Ganges, Brahmaputra and Meghna, combined with a declining measurement network and political challenges to sharing of data, satellite remote sensing of discharge has recently become a viable alternative. This study was motivated by the need to understand the geophysical sources of uncertainty of satellite interferometric-based discharge estimation in Bangladesh. A consequential goal of this study was to contextualize the understanding as a function of river's geophysical characteristics (river width, reach averaging length, bed/water slope) and also to explore a pragmatic approach to uncertainty reduction using water level climatology. Discharge was estimated according to the slope-area (Manning's) method using elevation data from SRTM (Shuttle Radar Topography Mission). A high resolution hydrodynamic model was accurately calibrated to simulate water level and flow dynamics along the river reaches of the river network and serve as reference for comparison with satellite-based estimates. It was found that satellite interferometric (SRTM)-based discharge estimates yielded estimation error variance an order smaller than the natural flow variability only if the river width was at least was three times larger the width of the native resolution of satellite elevation data. Rivers narrower than this width (for SRTM, this cut off is 270 m) yielded a coefficient of variation larger than 1 due to contamination of land elevation data in hydraulic parameter calculations. It was also found that water level climatology can be useful in significantly reducing the estimation uncertainty for these narrow rivers. While reach averaging length appeared insensitive to accuracy for wide rivers (width > 1 km), a few rivers seemed to have an optimal reach averaging length at which the highest accuracy is obtained.
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