NASA's SWOT Mission Will Provide First Detailed Map of Earth's Surface Water

NASA's $1.2 billion Surface Water and Ocean Topography satellite (SWOT) successfully launched from California on December 16, marking the start of an unprecedented mission to map Earth's water bodies.

“It’s a game changer,” Rosemary Morrow, oceanographer at the Laboratory of Space, Geophysical and Oceanographic Studies and one of the science leads for the mission, told Nature. “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.”

Developed over nearly two decades as part of a joint project with the French National Centre for Space Studies, SWOT will use advanced radar to measure the elevation, extent, and movement of water across the planet. Such insights will help researchers better understand the global water cycle and the impacts of climate change, and provide crucial information to help communities manage their water resources.

“From a societal point of view—whether you’re looking at drinking water, navigation, flood control— water needs to be managed at basin scale,” SWOT science team member Sylvain Biancamaria shared in a mission brief. “Therefore, observations covering the entire basin are needed, and SWOT will provide such data sets.”

An Unprecedented Map of Nearly All Earth’s Freshwater Sources

What’s perhaps most enlightening about SWOT’s mission is just how little data we currently have on Earth’s freshwater bodies. According to Tamlin Pavelsky, NASA freshwater science lead for SWOT, we only have information on a couple thousand lakes around the world. Thanks to the satellite’s ability to measure and map 95% of lakes greater than 15 acres (6 hectares) and rivers wider than 330 feet (100 meters) across, Pavelsky says that number will grow to “between 2 million and 6 million.”

By measuring and monitoring the height, extent, and surface area of nearly 1.3 million miles of Earth’s freshwater sources, the SWOT research team says they can more accurately gauge how climate change is impacting our planet’s water cycle. 

"This is important because as the climate warms, oceans are rising," Karen St. Germain, director of NASA's Earth Science Division, told reporters via ZDnet. "Our coastlines are changing, and we're seeing large fluctuations in inland water bodies—lakes, reservoirs and rivers." 

Magnifying Impacts From Climate Change

According to NASA, the ocean has absorbed more than 90% of the heat trapped by human-caused greenhouse gas emissions. Much of the continued uptake is thought to occur around currents and eddies less than 60 miles across, ocean features previously too small to study accurately from space. SWOT changes all of that, with a 10-fold improvement in the spatial resolution of water height measurement.

By better understanding how climate change is impacting eddies and currents, estimated to account for up to half the heat and carbon transfer from surface waters to the ocean’s depths, researchers hope they can determine the ocean’s ability to capture future heat and emissions. 

“What is the turning point at which the ocean starts releasing huge amounts of heat back into the atmosphere and accelerating global warming, rather than limiting it?” Nadya Vinogradova Shiffer, SWOT’s program scientist, said. “SWOT can help answer one of the most critical climate questions of our time.”

After six months of calibration, SWOT will enter an orbit roughly 554 miles above the planet and begin mapping its surface water. This process will repeat every 21 days, producing a steady stream of data that NASA plans to make public and provide tools for easier access. While the satellite has a scheduled lifespan of three years, SWOT project manager Thierry Lafon says we’ll likely have this advanced eye in the sky for decades to come. 

"Our system will not limit the lifetime if everything is OK on board," he told Space.com before launch. "Five years is completely reasonable, and [perhaps] many more years, as we've been doing for 30 years."