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SWOT

SWOT MIssionThe 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.

Instruments
  • KaRIn Ka-band Radar Interferometer will measure ocean and surface water levels over a 120-km (75-mi) wide swath with a ~20 km (~12 mi) gap along nadir. It will operate in two modes: 1) Low-Resolution over the ocean with significant onboard processing to reduce data volume and 2) High-Resolution over broad, primarily continental, regions defined by the SWOT Science Team, focusing on hydrology studies.
  • Poseidon-3 like Altimeter – There will be a Ku and C band nadir altimeter, similar to that of the Jason series. It measures altimeter range, sigma0, significant wave height and ionospheric correction in the gap between the KaRIn swaths. 
  • DORIS AntennaDoppler Orbitography and Radiopositiong by Satellite is a Precise Orbit Determination (POD) system. It receives at the 401.25 MHz and 2036.25 MHz frequencies. It is used for the all weather global tracking and calculates the orbit ephemeris. 
  • Microwave Radiometer –  It measures the 18.7 GHz, 23.8 GHz and 34.0 GHz sea surface microwave brightness temperatures. The 18.7 GHz channel provides the wind induced effects in the sea surface background emissions correction. The 23.8 GHz channel measures water vapor. The 34.0 GHz channel measures the cloud liquid water to be corrected. All together the three frequencies provide the error in the satellite range measurement caused by pulse delay due to water vapor.
  • X-band Antenna – will be used for high-rate data downlink to the ground station.
  • Laser Reflector Assembly – LRA is an array of mirrors that will provide a target for laser tracking measurements from the ground. It supports the calibration and validation for the POD.
  • GPS Receiver – will pick up tracking signals from the constellation of Global Positioning System satellites.
SWOT Data Products

Level 1B KaRIn Datasets:

  • KaRIn low-rate Earth located ocean interferogram in 9 beams and robustness products
  • Single look complex data
  • Radiometer brightness temperatures

Level 2 KaRIn Ocean Datasets:

  • Sea surface height, with uncertainties, no coarser than 2 km
  • Radar uncertainty measurements
  • Wind speed
  • Estimated sea surface slope vector

Level 2 Nadir Altimeter:

  • Nadir altimeter data consistent with the Jason-series Geophysical Data Records (GDR)

Level 2 KaRIn Surface Water Datasets:

  • Geo-located, pixel cloud water mask, regardless of surface area
  • Estimated surface water elevation, with uncertainty, for water bodies with area greater than 250 m2 and for rivers of width greater than 100 m
  • Estimated surface area represented by each point in the pixel cloud
  • River vector dataset (per pass and average) containing location, inundation area/extent, height, slope, width, and discharge with associated uncertainties and other relevant data
    • Reported discharge will be an estimate of the reach-averaged discharge, and the extent of the reach averaging will be selected to optimize global estimates of river discharge
    • River height accuracy of 10 cm or better over an area of 1 km2 inside the river mask
    • River water slope accuracy of 1.7 cm / 1 km or better for river widths greater than 100 m
  • Lakes and reservoirs vector dataset (per pass and average) containing location, water area/extent, height, storage change with associated uncertainties and other relevant data
    • Detected water bodies will be linked to an a priori database of water bodies, but provision will be made for collecting additional bodies
    • Height accuracy shall be 25 cm or better for water bodies whose surface area is 250 m2 - 1 km2
    • Height accuracy shall be 11 cm or better for water bodies whose non-vegetated surface area exceeds 1 km2
  • Raster product for wetlands and estuaries is expected to be provided
Animations

SWOT will collect data across a 120 km wide swath, with a gap in the center for an altimetry track. This animation shows the collection of data over the state of Florida, which is rich with rivers, lakes and wetlands. Globally, measurements will be taken both over the ocean and over freshwater areas. [Credit: NASA/JPL-Caltech]