The Surface Water and Ocean Topography (SWOT) mission aims to provide valuable data and information about the world's oceans and its terrestrial surface water such as lakes, rivers, and wetlands. SWOT is being developed jointly by NASA and Centre National D'Etudes Spatiales (CNES), with contributions from the Canadian Space Agency (CSA) and United Kingdom Space Agency (UKSA). The mission is targeted to launch September 2021.
SWOT will measure ocean surface topography and land surface water elevation with great accuracy, using interferometry to achieve two-dimensional mapping. Observations from SWOT can be used to better understand ocean currents and processes happening at spatial scales on the order of 15-150 km, something that has not been done before. SWOT will enable high resolution (within 1 km from land) monitoring of coastal regions, including coastal currents, storm surges, and regional sea level change. On land, SWOT will provide measurements of water storage changes (surface water area and water depth) of major lakes, reservoirs, rivers, and wetlands, and support derived estimates of river discharge, which aid in assessing water resources. SWOT will observe rivers wider than 100 m and lakes with a surface area of 15 acres or more (i.e., an outline of 250 m x 250 m or 820 ft x 820 ft).
SWOT will provide Low Rate (LR) data with low spatial resolution globally, and High Rate (HR) data with high spatial resolution for the terrestrial and coastal environments.
HR measurements will not be taken everywhere, due to bandwidth issues of downlinking the data. To resolve that, an HR mask will be used. Figure 1 below shows, in yellow, where the HR data will be made available. The areas not covered by the mask will be preprocessed to LR data. Figure 2 below shows the coverage and swath geometry of LR data at high and low latitudes. HR data will have terrestrial corrections applied, whereas LR data will only have oceanic corrections applied.
The table below summarizes the SWOT datasets. To search and access go to DATA section.
L1 = level 1; L2 = level 2; High Rate (HR); Low Rate (LR)
To learn more about the mission, go to SWOT Mission page.
The ocean will be observed at a Low Rate (LR) with low spatial resolution. The LR data will have oceanic corrections applied. Figure 1 below shows the coverage and swath geometry of LR data at high and low latitudes.
SWOT will provide the very first comprehensive view of Earth's surface inland water bodies from space and will allow scientists to determine changing volumes of inland water across the globe at an unprecedented resolution. Hydrologists will use the data to calculate the rate of water gained or lost in lakes, reservoirs, and wetlands as well as discharge variations in rivers, globally. These measurements are key to understanding surface water availability and in preparing for important water-related hazards such as floods and droughts. To learn more about the mission go to SWOT Mission page.
The SWOT Hydrology objectives are to 1) provide a global inventory of all terrestrial water bodies (lakes, reservoirs, wetlands) whose surface area exceeds 250 m by 250 m (~820 ft by ~820 ft) and rivers whose widths exceed 100 m (~330 ft); 2) Measure the global storage change in freshwater bodies at sub-monthly, seasonal, and annual time scales; 3) Estimate the global change in river discharge at sub-monthly, seasonal, and annual time scales.
Terrestrial water features (rivers, lakes, reservoirs) will be observed at a High Rate (HR) with high spatial resolution. HR measurements will not be taken everywhere, due to bandwidth issues of downlinking the data. To resolve that, an HR mask will be used. The areas not covered by the mask will be preprocessed to a Low Rate (LR) with low spatial resolution. Figure 1 below shows, in yellow, where the HR data will be made available. The HR data will have terrestrial corrections applied.
The SWOT satellite will survey rivers wider than 100 m (328 ft). Three datasets will be available to users, including pixel cloud, raster, and vector. They will only be generated for rivers recorded in an existing database and will cover reaches of approximately 10 km (6 mi).
Each orbit that the satellite makes is split at the poles into two passes. Shown in the map below are three different passes that will observe the Sacramento River, CA, USA.
The data gathered by the satellite will be divided into tiles, the spatial granule used for distributing the data. Each tile extends approximately 64 km along-track and 64 km perpendicular to the pass. The footprints of four different tiles are shown on the map. Note: the tiles shown are not the same as those SWOT will use, as their along-track locations and extents were chosen for illustration purposes only.
For more details on the SWOT terrestrial hydrology datasets, and other SWOT mission information, go to SWOT Mission page.
SWOT will make continuous measurements, regardless if over land or ocean. So the transitional areas between land and sea will be measured, whether it is an estuary, river delta, or coast from the surf zone to the continental shelf. The spatial resolution of measurements will differ depending on how far away from land the satellite is. See the Spatial Coverage section for more information.
To find out more about SWOT and coastal areas, the mission wrote a white paper on estuaries and near shore processes and coastal seas and shelf processes.
Coastal areas will be observed at a High Rate (HR) with high spatial resolution. HR measurements will not be taken everywhere, due to bandwidth issues of downlinking the data. To resolve that, an HR mask will be used. The areas not covered by the mask will be preprocessed to a Low Rate (LR) with low spatial resolution. Figure 1 below shows, in yellow, where the HR data will be made available. HR data will have terrestrial corrections applied. If oceanic corrections are needed, users will need to add those themselves.