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).
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.
Datasets Release Schedule
The table below provides the tentative schedule for SWOT data product releases at the PO.DAAC.
1 Pre-validated products have not completed validation and may contain known anomalies and limitations. Products may not cover all available data since launch and/or may be affected by some evolution of science data processing algorithms and instrument calibrations based upon incoming in-flight data. Products may include partial coverage of river discharge and lake storage change, due to limited temporal sampling.
2 Validated products have completed validation by the SWOT science team. Products include river discharge and lake storage change for water bodies covered by more than one year of validated products. One seasonal cycle of observations is expected to provide scientifically useful algorithm input parameters.
Standard Data Products
The table below summarizes SWOT data products, along with product descriptions and sample data products where available. The release note for these sample files is SWOT Sample Data Products v1.2 and all samples can be downloaded here.
To learn more about the mission, go to SWOT Mission page.
SWOT will revolutionize oceanography by detecting ocean features with 10 times better resolution than present technologies. The higher resolution of SWOT is required to distinguish structures that occur on scales of 100 kilometers or shorter, where most of the ocean's energy is mixed and transported. Such small-scale ocean features contribute to the ocean-atmosphere exchange of heat and carbon, major components in global climate change. Moreover, SWOT's detailed information on ocean circulation will improve understanding of the ocean environment including motion of life-sustaining nutrients and harmful pollutants. To learn more about the mission go to SWOT Mission page.
The SWOT Ocean objective is to characterize the ocean mesoscale and sub-mesoscale circulation (15 – 200 km or about 9 – 124 mi) at spatial resolutions of 15 km (9 mi) and greater.
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.
The table below summarizes the SWOT data products, along with product descriptions and sample data products where available. The release note for these sample files is SWOT Sample Data Products v1.2 and all samples can be downloaded here.
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).
A pass is half an orbit/revolution that starts and ends at the poles. Shown in Figure 2a below are three different passes (purple, green, and yellow) that would observe the Mississippi River, USA, as it drains into the Gulf of Mexico.
The data gathered by the satellite will be divided into tiles (Figure 2b), the spatial granule used for distributing the data. Each tile extends approximately 64 km along-track and 64 km perpendicular to the pass.
Note: the tiles shown are not the same as what SWOT will observe, as their along-track locations and extents were chosen for illustration purposes only.
(a) Illustration of three different passes observing the Mississippi River as it drains into the Gulf of Mexico, in North America.
(b) Illustration of a data tile that is 64 km by 64 km, the spatial granule used for distributing certain SWOT hydrology data products. Images are for illustration purposes only; actual exact SWOT tracks may not match what is shown here.
Images are for illustration purposes only; actual exact SWOT tracks may not match what is shown here.
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.