Radar altimetry has revolutionized oceanography by providing global measurements of ocean surface topography (OST [e.g., Fu and Cazenave, 2001]). Long-term measurements of large-scale circulation and heat storage of the global oceans have led to discoveries such as the effects of changes in ocean circulation on climate (e.g., El Niño and La Niña). A critical limitation, however, is the 200- to 300-kilometer spacings between satellite orbital tracks, which are unable to resolve the currents and oceanic mesoscale processes that contain 90% of the kinetic energy of the oceans.
In contrast to ocean observations, surface freshwater measurements are limited mostly to in situ networks of gauges that record water surface elevations at fixed points along river channels. Globally, the spatial and temporal distribution of water stored on the land surface and moving through river channels is known only crudely. Furthermore, water movement in wetlands and across floodplains throughout the world is essentially unmeasured, significantly limiting our understanding of flood processes.
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