New NASA Mission Will Study Earth's Surface Water From Space

The SWOT mission will measure the height of the world's oceans, rivers and lakes, helping scientists measure how fresh and saltwater bodies change over time. NASA/JPL-Caltech

A new satellite scheduled for launch early Thursday morning will enable scientists to survey nearly all of the water on Earth's surface and provide the most detailed information yet on the state of oceans, lakes and rivers and how they change over time.

The Surface Water and Ocean Topography (SWOT) satellite, a collaboration between NASA and the French space agency Centre National d'Études Spatiales (CNES), will provide knowledge crucial for coping with climate change and protecting the global supply of water for drinking and irrigation, a panel of scientists explained Dec. 13, 2022, at a news conference at Vandenberg Space Force Base in California.


The satellite is set to be launched into orbit aboard a SpaceX rocket at 6:46 a.m. Eastern time Dec. 15 from Vandenberg Air Force Base. The Canadian Space Agency and U.K. Space Agency also are contributing to the mission.

What Is SWOT?

SWOT will rely on a satellite altimeter that will use radar interferometry to make high-resolution measurements over two wide swaths of water at once, with a conventional nadir altimeter in the gap in between. CNES

SWOT's instruments will help scientists understand where water is, where it's coming from and where it's going, Katherine Calvin, NASA's chief scientist and senior climate adviser, said at the news conference.

"It's going to allow us to observe ocean features with higher resolution. Oceans absorb a lot of carbon and heat," Calvin said. "And this will give us a better understanding of those processes and help us improve both our understanding of the oceans, as well as our projections into the future."


Additionally, SWOT will provide the first global survey of water running through rivers and lakes. But not just that. The science instruments will provide views of Earth's freshwater bodies and oceans in unprecedented clarity. NASA describes it as being similar to how a high-definition television picture looks compared to a picture on an older TV.

SWOT's most important system is the Ka-band Radar Interferometer (KaRIn), a special type of altimeter that records the delay between the radar signals measured by two antennae to calculate the height of bodies of surface water. It uses JPL-developed instrument technology and radar interferometry to measure ocean and surface water levels in two modes:

  • Low-resolution over the ocean with significant onboard processing to reduce data volume.
  • High-resolution over broad, primarily continental, regions focusing on hydrology studies.

SWOT, which has been in development since 2016, will cost NASA an estimated $755 billion throughout its operational lifetime, with the French space agency chipping in another $400 billion, according to a 2018 NASA auditing report.


Why Is SWOT's Mission Important?

Earth's water distribution
This bar chart shows how almost all of Earth's water is saline and is found in the oceans. Of the small amount that is actually freshwater, only a relatively small portion is available to sustain human, plant and animal life. USGS/Igor Shiklamonov

One reason SWOT is important is that water covers so much of Earth's surface — 71 percent, according to the U.S. Geological Survey (USGS). About 96.5 percent of the planet's H2O is contained in the oceans. The remaining water is in rivers, lakes, icecaps and glaciers, and in the ground as soil moisture and aquifers.

But that water never really sits still in one place, due to the water cycle, in which water constantly moves from one place to another and switches forms. But global warming and climate change also are impacting the water cycle.


"[Climate change] has a huge impact today ... on the water cycle, accelerating the water cycle by putting some drought in some parts of the world and floods in other parts," said Selma Cherchali, Earth observation program head at CNES. But until now, scientists have been stymied by the limitations of their knowledge due to insufficient data.

The new satellite will give scientists a look at that supply and demand chain in order for them to study Earth's water as a complete process.

It won't be just NASA and CNES scientists who'll be using SWOT data. Researchers from 17 different countries are involved in the project, and eventually the data will be made accessible to anyone in the public who wants to analyze it.

Nadya Vinogradova Shiffer, SWOT program scientist at NASA, described monitoring and predicting the movement of water across the planet as a worthy investment.

"We as humanity depend on Earth water to survive and prosper," Shiffer said. "We know that oceans are the ultimate source of all moisture and water on Earth. Think of oceans as huge warehouses that supply moisture and water to lands that we rely on for our drinking water, agriculture and industry."

Knowing how much water is on Earth in various places also can help efforts to cope with water shortages in some places and rising seas and vanishing shorelines in others. SWOT data might help scientists to spot those patterns in advance, based on the supply wherever the water originates.

"The breakthrough is that we're going to look at Earth water with a very high resolution and clarity, like never before," Shiffer said. She said the images would be 10 times as detailed and clear as previous satellite images.


What SWOT Can Teach Us

Members of the international Surface Water and Ocean Topography (SWOT) mission test one of the antennas for the Ka-band Radar Interferometer (KaRIn) instrument in a clean room at NASA’s Jet Propulsion Laboratory in Southern California. NASA/JPL-Caltech

SWOT is expected to provide new insights about ocean turbulence, and how the movement of seawater transports large amounts of kinetic energy, heat, mass, salt nutrients, carbon and plastic pollution across the planet's surface.

That data, in turn, could improve climate modeling and help scientists to make better predictions about global warming, because the oceans absorb substantial amounts of solar heat.


"Half of the vertical transport of this heat absorption from the surface to the deep ocean is done by turbulence," Shiffer said. "The turbulence matters; perhaps it is turbulence that is the missing climate puzzle piece that we've never observed."

SWOT's instrumentation is so sensitive that it will be able to detect any lakes larger than 15 acres (6.07 hectares) and all the world's rivers that measure wider than 330 feet (100 meters).

Current satellites only make it possible to get data for about 1,000 of Earth's lakes scattered across the world. Compare that to the millions of lakes SWOT will be able to observe, and you can see why it's such an important mission.