Billion-dollar NASA satellite launches to track Earth’s water

SWOT satellite will bounce radar off water bodies to give scientists a new window into climate change and the global water cycle.

From swirling ocean eddies that help shape the global climate to millions of lakes and rivers, scientists are about to get an unprecedented view of Earth’s water.

The US$1.2-billion Surface Water and Ocean Topography satellite (SWOT), which launched at 6.46 a.m. Eastern time on 16 December from the Vandenberg Space Force Base in California, promises to transform research into the global water cycle and provide climate scientists with a fresh lens on a warming world.

A joint mission led by NASA and the French National Centre for Space Studies, SWOT will bounce radar off the surface of Earth’s water bodies — including many that are too small to be tracked from space by current methods. The satellite will enable scientists to measure and track the elevation, extent and movement of water across the planet in ground-breaking detail.

“It’s a game changer,” says Rosemary Morrow, an oceanographer at the Laboratory of Space, Geophysical and Oceanographic Studies in Toulouse, France and one of the science leads for the mission. “It will be like putting on a pair of glasses when you are short-sighted: things are sort of vague, and then suddenly everything comes into clarity.”

Lakes and rivers

There are currently publicly available data for just 10,000–20,000 of the roughly 6 million lakes and reservoirs larger than one hectare on the planet today, says Tamlin Pavelsky, a hydrologist at the University of North Carolina at Chapel Hill and another of SWOT’s science leads. SWOT will measure nearly all 6 million every 10 or 11 days. “We’ve never had measurements like this before,” says Pavelsky. “We don’t even have a baseline.”

In 2021, a team led by Sarah Cooley, a geographer at the University of Oregon in Eugene, pieced together existing satellite measurements of surface area and water elevation for some 227,000 lakes, but Cooley says those are available only every 90 days. “The data that will be provided by SWOT is orders of magnitude beyond what we were able to do,” says Cooley.

SWOT has already helped to generate advances in river hydrology. In anticipation of the satellite’s launch, researchers developed new ways to convert measurements of water height, extent and elevation change into flow estimates. Applying those techniques to existing satellite data, scientists estimated that rivers carried up to 17% more fresh water into the Arctic Ocean between 1984 and 2018 than previously thought; SWOT is expected to refine this estimate while enabling similar work across the globe.

“If SWOT does what we think it’s going to do, it’s going to change the face of hydrology,” says Colin Gleason, a geographer at the University of Massachusetts Amherst and an author of both studies.

Ocean eddies

Similar advances are expected at sea, where SWOT is expected to provide high-resolution measurements that will allow scientists to track currents, swirling eddies and the ebb and flow of tides. These will bolster understanding of water circulation and improve high-resolution models that can track the transfer of heat and carbon dioxide from the warming atmosphere into the depths of the ocean.

SWOT will give scientists their first 3D view of eddies, for example, and will be able to detect perturbations around 10 kilometres wide — one-tenth the scale of the best measurements that are currently available, says Morrow. Even these small features are crucial to understanding and predicting the climate, she says.

An international consortium involving the United States, France, Australia and others is planning field expeditions at 18 ocean sites around the world next year. These will help to calibrate the SWOT data against on-site measurements under a variety of ocean conditions.

“We’re really really excited, but the proof is in the pudding,” Morrow says. “We’re waiting to see what information comes out.”

Source: Nature News


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