Why NASA’s new mission will study Earth’s water from space

Before sunrise Thursday, a rocket carrying the Surface Water and Ocean Topography Satellite will lift off from Vandenberg Space Force Base north of Santa Barbara.

When SWOT reaches its destination 553 miles above the Earth’s surface, a new era in the study of climate change will begin.

The satellite will be the first to study nearly all of the world’s surface water, allowing researchers to constantly monitor the volume and movement of every ocean, river, lake and stream on the planet.

This joint mission by NASA and France’s National Center for Space Studies is supported by a unique alliance of Earth scientists eager to answer key questions about floods, climate patterns and our future water supply.

The satellite will be able to see through storm clouds and accurately measure the height of flood waters when ground gauges are submerged. If a country refuses to share information about its water use along a river, the spacecraft will be able to provide it.

SWOT is designed to observe the planet with unprecedented precision and frequency, returning reams of data to help scientists and policy makers plan for floods, droughts and sea level rise.

Scientists say the $1.2 billion mission has the potential to change our understanding of Earth’s water as significantly as the microscope changed our view of the human body.

“The possibilities are so endless that I’m almost not sure where to start,” said Tamlin Pavelsky, a global hydrologist at the University of North Carolina at Chapel Hill and the mission’s hydrology science lead. “It’s like hitting a piñata with a baseball bat and having all this candy pour out, and you don’t even know what to grab first.”

Previous satellites have monitored oceans or fresh water. SWOT will be the first to observe both. The mission is a joint effort in oceanography and hydrology, two related scientific disciplines that are often separate.

“The whole water cycle is really important to understanding how climate change is affecting Earth’s surface processes, and not just water transport, but also heat,” said Patrick Barnard, director of US Geological Survey’s Pacific Coastal and Marine Science research. Santa Cruz center that is not affiliated with the mission.

The data collected by SWOT, he said, “will go a long way in our understanding of not only climate change, but also climate variability and how that affects droughts and things like monsoons.”

The satellite’s main instrument is the Ka-band Radar Interferometer, or KaRIn. The satellite sends out radio waves and KaRIn records how much energy returns to the satellite and how long it takes to arrive. Along with other measurements, these return signals tell the satellite whether it is detecting water and the height of that water’s surface.

This animation shows how SWOT will collect data on Florida's rivers, lakes, and wetlands.

This animation shows how SWOT will collect data on Florida’s rivers, lakes, and wetlands. Globally, action will be taken over both the ocean and freshwater areas.


Once fully operational in June, SWOT will scan everything between the Arctic Ocean and Antarctica at least once every 21 days. The initial mission will last for three years.

“Right now we have satellites that can tell us where the water is, and we have satellites that can tell us what the elevation of the water is, but we don’t have satellites that can do both at the same time. And that’s the kind of killer stuff that KaRIn can do,” Pavelsky said. “It takes the world’s water from 2D to 3D.”

For fresh water, SWOT will provide the first comprehensive survey of the planet’s network of rivers, lakes and streams, which are too numerous – and often too remote – to consistently track from the ground.

“I can finally use a remote sensing method to estimate current flow, instead of relying on current measuring stations, which are quite sparsely distributed,” said Aakash Ahamed, a PhD candidate in geophysics at Stanford University.

Sarah Cooley, a surface water hydrologist at the University of Oregon, monitors natural reservoirs and lakes to determine how climate change and human behavior affect water storage. Their work has been based on NASA’s ICESat-2 laser altimeter satellite, which provides data on the world’s 227,000 largest lakes and reservoirs two to four times a year. It is the most sophisticated surface water satellite technology available today.

That’s about to change. SWOT will return data from up to 6 million bodies of water at least once every three weeks. The satellite can detect almost all rivers that are at least 100 feet wide and all lakes larger than 15 acres.

“It’s a huge, huge difference,” Cooley said. “It’s actually crazy to think about what that’s even going to look like and how we’re going to work with that data.”

The surface water and ocean topography satellite is moved to a shipping container at Vandenberg Space Force Base.

The surface water and ocean topography satellite is being moved to a shipping container at Vandenberg Space Force Base in California, where it will be placed into orbit on Wednesday.

(Chris Okula / USSF 30th Space Wing)

SWOT will also make a big difference in how scientists monitor changes in the ocean.

Since 1992, sea level data has been largely measured by TOPEX/Poseidon and other satellite altimetry systems, along with a network of tide gauges that scientists assembled in various countries, agencies, and research institutions. These gauges provide only sporadic snapshots of any given coastline, and when a storm or high-tide flood submerges a neighborhood, scientists trying to measure the tide level usually rely on the nearest tide gauge, often located at miles away

And altimeters already in orbit, while groundbreaking for more than a generation of oceanographers, have a blind spot: They can’t take measurements right at the tide line. The nearest they can get is about 6 miles from the coast; in many places, readings are taken up to 18 miles offshore.

“We don’t really know exactly what’s going on. at coast,” said Benjamin Hamlington, a research scientist at NASA’s Jet Propulsion Laboratory in La Cañada Flintridge who is guide the science of sea level rise in the mission. “That’s where SWOT will come in.”

Research scientist Benjamin Hamlington speaks at NASA's Jet Propulsion Laboratory in La Cañada Flintridge.

Benjamin Hamlington, a research scientist at NASA’s Jet Propulsion Laboratory in La Cañada Flintridge, said the SWOT mission will collect data that is critical to our understanding of climate change.

(Carolyn Cole/Los Angeles Times)

The new satellite will also measure more subtle features in the open ocean that other satellites have never been able to clearly capture. These smaller-scale currents and circulation patterns play an important but little-known role in how the ocean absorbs heat, and where it ultimately goes. (The ocean, it’s worth noting, has absorbed more than a quarter of the carbon dioxide released by humans since the Industrial Revolution, and about 90% of the resulting heat.)

That knowledge is critical to our understanding of climate change, said Hamlington, who also leads NASA’s Sea Level Change Team. Coastal flooding is expected to occur with greater frequency and intensity in the coming decades, and SWOT data will significantly improve the forecasts communities rely on to prepare for this future.

Barnard, who oversees USGS research on climate impacts and coastal hazards along the West Coast and across the Pacific Ocean basin, said satellite technology has completely revolutionized his field.

Traditionally, a researcher might spend several years studying a single beach, lake or river valley. The scientific community would then integrate this work into the great puzzle of the Earth system.

In the past decade, Barnard and his team recruited scientists in Japan, Australia, New Zealand and Canada to study how El Niño and changing climate conditions have increasingly threatened coastal communities in the Pacific basin. It took 200,000 hours to collect and analyze data from 48 beaches on three continents, ultimately accounting for only 124 of the 6,200 miles of sandy coastline along the Pacific Rim.

“Now, from space, we can get a lot of information every day, if we really wanted to, and from anywhere in the world, which is mind-blowing,” Barnard said.

SWOT will not completely replace boots-in-the-sand fieldwork. During the first years of the mission, scientists will need to validate their results through extensive field measurements.

The large amount of data that SWOT will return presents its own challenges. Storing and managing this amount of information is a major task in itself.

It is also stimulating. Researchers say transformative technology like SWOT not only provides new answers to existing problems, but raises new questions entirely, said Cooley, the Oregon surface water hydrologist.

“This is really exciting as a scientist,” she said.

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