Astronomy:Surface Water Ocean Topography

SWOT (Surface Water & Ocean Topography)

Artist’s rendering
Mission type	Hydrology, Oceanography
Operator	NASA, CNES
Mission duration	Planned: 3,5 years
Spacecraft properties
Launch mass	200 kg (440 lb)
Start of mission
Launch date	April 16 17, 2021 (2017-04-16UTC20:21)
Rocket	Falcon 9
Launch site	Vandenberg Air Force Base SLC-4E
Contractor	SpaceX
Orbital parameters
Reference system	Geocentric
Regime	Low Earth
Semi-major axis	726.87189 km (451.65725 mi)
Eccentricity	0.00105
Inclination	77.6°
Period	112.42 minutes
Repeat interval	20.86455 days
Instruments KarIn Altimeter, Altimeter-Interferometer Synthetic Aperture Radar Microwave Radiometer Poseidon-3C Ku/C nadir altimeter DORIS Doppler Orbitography and Radiopositioning Integrated by Satellite Global Positioning System Payload Laser Retroreflector

The Surface Water Ocean Topography (SWOT) Mission is a future satellite mission, jointly developed by NASA and CNES, the French space agency, in partnership with 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 and to observe the fine details of the ocean's 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 in rivers, lakes and floodplains. In the world’s oceans, SWOT will also observe ocean circulation at unprecedented scales of 15-25 km, approximately an order of magnitude finer than current satellites, over the global oceans. 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-lived partnership between NASA and CNES to measure the surface of the ocean using radar altimetry that 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 120-kilometer wide swath with a ±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 (250 m)² lakes and 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.

Applications

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 river basins.

More accurate weather and climate forecasting

SWOT will enable more accurate weather and climate forecasting, especially seasonal. The quality of weather and climate forecasting largely depends on numerical modeling that use 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 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 disastrous of natural phenomena. Altimetry data from the SWOT mission will make it possible to measure floodwater levels and local topographic details more reliably.

Coastal ocean dynamics

Coastal ocean dynamics are important for many societal applications. They have smaller spatial and temporal scales than the dynamics of the open ocean and require finer-scale monitoring. SWOT will provide global, high-resolution observations in coastal regions for observing coastal currents and storm surges. While SWOT is not designed to monitor the fast temporal changes of the coastal processes, the swath coverage will allow us to characterize the spatial structure of their dynamics when they occur within the swath.

Reducing environmental risk and contributing to public policy-making

More generally, SWOT will help improve our knowledge, enhance observations by collecting data over the long term and making them available, and help us draw lessons from past episodes. Water resources, natural risks (floods, climate change, hurricane forecasting, etc.), biodiversity, health (preventing the propagation of epidemics), the agricultural sector, energy (including the management of electricity production and offshore gas and oil rigs), territorial development; all these areas and more stand to benefit from this new space mission.

Satellite characteristics

KaRIN instrument principle.

The primary instrument on SWOT is based a new type of radar instrument called the Ka-band Radar Interferometer (KaRIN), which uses radar interferometery and synthetic aperture (SAR) technology. 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. . A conventional altimeter will also be flown, and measure just beneath the satellite, as was done on the Topex/Poseidon, Jason series and Saral missions. Launch by a SpaceX Falcon 9 rocket is planned for April 2021. SWOT will have a mission lifetime of three years and a half.

Project status

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 much more detailed measurements of the ocean surface than ever before.

External links

• Surface Water Ocean Topography project web site
• Ocean Surface Topography from Space web site
• Cnes project Library
• Aviso Altimetry future mission page on SWOT