Surface Water Ocean Topography Mission

The Surface Water Ocean Topography (SWOT) Mission is a proposed NASA mission to make the first global survey of Earth’s surface water. It is one of 15 missions that the 2007 National Research Council’s decadal survey of Earth science recommends NASA implement in the coming decade.

SWOT is being developed by an international group of hydrologists and oceanographers to provide a better understanding of the world's oceans and its terrestrial surface waters. It will give scientists their first comprehensive view of Earth’s freshwater bodies from space and more much detailed measurements of the ocean surface than ever before.

SWOT is collaboration between NASA and CNES, the French space agency. It is currently being designed and constructed at NASA's Jet Propulsion Laboratory (JPL). It builds on the very successful 25-year partnership between the two agencies to use radar altimetry to measure the surface of the ocean that began with the TOPEX/Poseidon mission.

The SWOT mission is based on a new type of radar called Ka-band radar interferometery. The satellite will fly two radar antennae at either end of a 10-meter (33-foot) mast, allowing it to measure the elevation of the surface along a 120- kilometer (75-mile)-wide swath below. The new radar system is smaller but similar to the one that flew on NASA’s Shuttle Radar Topography Mission, which made high-resolution measurements of Earth’s land surface in 2000.

The mission’s science goals are to
 * Provide sea surface heights and terrestrial water heights over a 120-kilometer wide swath with a plus or minus 10-kilometer gap at the nadir track.
 * Over the deep oceans, provide sea surface heights within each swath with a posting every two kilometers x two kilometers, and a precision not to exceed 0.5 centimeters when averaged over the area.
 * Over land, download the raw data for ground processing and produce a water mask able to resolve 100-meter-wide rivers and one-quarter-kilometer-square lakes, wetlands, or reservoirs. Associated with this mask will be water level elevations with an accuracy of 10 centimeters and a slope accuracy of one centimeter/one kilometer.
 * Cover at least 90 percent of the globe. Gaps are not to exceed 10 percent of Earth's surface.

SWOT will have a mission lifetime of three years.