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WatER: The proposed Water Elevation Recovery satellite mission

Nelly Mognard(1) , Doug Alsdorf(2) , and Ernesto Rodriguez(3)

(1) CNES, 18, ave. E. Belin, 31401 Toulouse Cedex 9, France
(2) Ohio State University, 275 Mendenhall Laboratory, Columbus, OH 43210-1308, United States
(3) California Institute of Technology, Orange Grove Dr., Pasadena, CA, United States


WatER Participants: over 150 people from more than 20 countries

Surface fresh water is essential for life, yet we have surprisingly poor knowledge of the spatial and temporal dynamics of surface water storage and discharge globally. The core mission objective is to describe and understand the continental water cycle and the hydrological processes (e.g., floodplain hydraulics) at work in a river basin. The key question that will be answered by WatER is: "Where is water stored on Earth's land surfaces, and how does this storage vary in space and time?" WatER will facilitate societal needs by (1) improving our understanding of flood hazards; (2) freely providing water volume information to countries who critically rely on rivers that cross political borders; and (3) mapping the variations in water bodies that contribute to disease vectors (e.g., malaria).

Conventional altimeter profiles are incapable of supplying the measurements needed to address scientific and societal questions. WatER will repeatedly measure the spatially distributed water surface elevations (h) of wetlands, rivers, lakes, reservoirs, etc. Successive h measurements yield δh/δt, (t is time), hence a volumetric change in water stored or lost. Individual images of h yield δh/δx (x is distance), hence surface water slope, which is necessary for estimating streamflow. WatER's main instrument is a Ka-band Radar INterferometer (KaRIN) which is the only technology capable of supplying the required imaging capability of h. KaRIN has a rich heritage based on (1) the many highly successful ocean observing radar altimeters, (2) the Shuttle Radar Topography Mission (SRTM), and (3) the development effort of the Wide Swath Ocean Altimeter (WSOA). The interferometric altimeter is a near-nadir viewing, 120 km wide swath instrument that uses interferometric SAR processing of the returned pulses to yield single-look 5m azimuth and 10m to 70m range resolution, with an elevation accuracy of approximately 50 cm. Polynomial based averaging of heights along the water body increases the height accuracy to about 3 cm. The entire globe is covered twice every 16 days, and orbit subcycles allow the average visit to be about half this time at low to mid-latitudes, and almost daily at high latitudes. The WatER mission is an international effort with a large, supporting scientific community. It has been proposed as an ESA Earth Explorer Core mission and will also be jointly submitted to NASA's Earth System Science Pathfinder program. WatER is designed to meet high priority targets for all nations and will provide essential data for the EU Water Framework Directive and the European Flood Alert System. WatER will meet the United Nations call for a "greater focus on water related issues" responds to the hydroclimatological needs of the International Working Group on Earth Observations, and answers the U.S. federal government call to focus on our "ability to measure, monitor, and forecast U.S. and global supplies of fresh water".


Workshop presentation


                 Last modified: 07.10.03