The Surface Water and Ocean Topography (SWOT) mission is a satellite altimeter jointly developed and operated by NASA and CNES, the French space agency, in partnership with the Canadian Space Agency (CSA) and UK Space Agency (UKSA). The objectives of the mission are to make the first global survey of the Earth's surface water, to observe the fine details of the ocean surface topography, and to measure how terrestrial surface water bodies change over time.
While past satellite missions like the Jason series altimeters (TOPEX/Poseidon, Jason-1, Jason-2, Jason-3) have provided variation in river and lake water surface elevations at select locations, SWOT will provide the first truly global observations of changing water levels, stream slopes, and inundation extents in rivers, lakes, and floodplains. In the world's oceans, SWOT will observe ocean circulation at unprecedented scales of , approximately an order of magnitude finer than current satellites. Because it uses wide-swath altimetry technology, SWOT will almost completely observe the world's oceans and freshwater bodies with repeated high-resolution elevation measurements, allowing observations of variations.
Context
SWOT builds on a long-standing partnership between NASA and CNES to measure the surface of the ocean using radar altimetry. This partnership began with the TOPEX/Poseidon mission (launched in 1992) and continued with the Jason series. SWOT brings together the hydrology and oceanography communities and will extend the precise, high-resolution surface topography observations into the coastal and estuarine regions.
Scientific objectives
The mission's science goals are to: Provide sea surface heights and terrestrial water heights over a wide swath with a ± gap at the nadir track. Over the deep oceans, provide sea surface heights within each swath with a posting every , and a precision not to exceed at , or at when averaged over the area. Over land, download the raw data for ground processing and produce a water mask able to resolve wide rivers and lakes and reservoirs. Associated with this mask will be water level elevations with an accuracy of for water bodies whose non-vegetated surface area exceeds . The slope accuracy is over a maximum of flow distance. The satellite will overfly Earth from 78° S to 78° N, covering at least 86% of the globe.
SWOT retraces the same path over the Earth's surface every 21 days, during 292 orbits. It is designed for a mission lifetime of three years.
Mission
SWOT is designed for the study and monitoring of inland waters and the oceans, such as:
Management of water-sharing issues
The sharing of river water often causes friction between neighboring states, especially when there is no common technology for verification. SWOT will provide global information as input for systems monitoring transboundary river basins, including measurements of variations in reservoir water storage and estimates of river discharge.
More accurate weather and climate forecasting
SWOT will enable more accurate weather and climate forecasting, especially seasonally. The quality of weather and climate forecasting largely depends on numerical modeling that uses the state of the ocean surface and the hydrological conditions of catchment areas in their initial and boundary conditions.
Managing freshwater for urban, industrial, and agricultural consumption
Accurate knowledge of sources of available water is a key factor in decision-making for organizations involved in the distribution of water for agricultural, urban, and industrial needs. Data from SWOT will contribute at a global level by providing water supply services and distribution companies with information about major reservoirs and the largest rivers and catchment areas, thus enabling them to plan the management of water stocks further into the future.
Improved flood modeling
Flooding, whether from rivers overflowing their banks or in coastal regions, is among the most costly natural disasters. Altimetry data from the SWOT mission will make it possible to measure the 3-dimensional shape of flood waves, track floodwater levels, and improve measurements of local topographic details in floodplains. All of these will improve prediction capabilities for future floods.