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Why a Hydrology Mission Needs Two-Dimensional Acquisitions of Water Surface Elevations

Douglas Alsdorf(1) , Paul Bates(2) , Dennis Lettenmaier(3) , Delwyn Moller(4) , Ernesto Rodriguez(4) , and Matt Wilson(5)

(1) Ohio State University, 275 Mendenhall Lab, 43210 Columbus Ohio, United States
(2) University of Bristol, University Road, Bristol BS8 1SS, United Kingdom
(3) University of Washington, 164 Wilcox Hall, 98195 Seattle Washington, United States
(4) Jet Propulsion Laboratory, 4800 Oak Grove, 91109 Pasadena California, United States
(5) University of Exeter, Treliever Road, Penryn TR10 9EZ, United Kingdom


A fundamental problem in our understanding of the global water cycle is the measurement and prediction of water flows across floodplains and wetlands. Fresh water bodies cover at least 4% of the earth’s terrestrial surface whereas tropical wetlands, particularly in the Amazon Basin, occupy nearly 20% of their watershed. These vast water bodies are significant stores of freshwater that are often unaccounted in climate and water cycle models. Predictions of flooding discharge and related societal hazards are particularly difficult because the flows are spatially complex with both vast diffusive and locally confined hydraulics. This complexity leads to a rich variety of carbon, nutrient, and sediment dynamics within the wetland ecology. However, our ability to model and hence predict the hydrologic, ecologic, and societal consequences of floods is greatly limited by the complete lack of water height (h) measurements virtually anywhere on the globe during the passage of any given flood wave. Using spaceborne interferometric synthetic aperture radar (SAR) measurements, we show that changes in flood water heights (dh/dt) are far more complex than typically assumed. Typical modeling approaches assume that floodplain waters are horizontal and equivalent to those measured in the adjacent main channel yet such assumptions do not match our observed measurements. Instead, we find that during the passage of a flood wave geomorphic features such as small floodplain channels can act as not only as conduits of flow, but surprisingly as barriers. Both point-based stream gauge and profiling altimetric methods of measuring these water surface elevations and their changes are incapable of capturing the inherent dynamics. For example, using a profiling altimeter and a 16-day orbital repeat cycle, like that of Terra, misses ~30% of the rivers and ~70% of the lakes in the global data bases. Restricting the study to the largest rivers and lakes provides better coverage, but significant water bodies are still missed. Furthermore, the rivers which are covered can have only a few visits per cycle, leading to problems with slope calculations. Instead, a high-resolution, image-based approach with broad, two-dimensional acquisitions of h, dh/dt, and dh/dx are required to answer important hydrologic questions. A 120 km wide swath instrument misses very few lakes or rivers: ~1% for 16-day repeat and ~7% for 10-day repeat. Therefore, an international team is proposing the Water Elevation Recovery mission (WatER). A key technology of the WatER mission is a Ka-band Radar INterferometer (KaRIN) which is capable of the required high-resolution 2D measurements.


Workshop presentation


                 Last modified: 07.10.03