A NASA satellite designed to monitor Earth's water has revealed previously uncharted underwater features with remarkable precision, thanks in part to technology developed at Pasadena's Jet Propulsion Laboratory (JPL).
The Surface Water and Ocean Topography (SWOT) mission, a collaboration between NASA and the French space agency Centre National d'Études Spatiales, has produced one of the most detailed maps of the ocean floor ever created, according to research published in the journal Science in December 2024.
This animation shows seafloor features derived from SWOT data on regions off Mexico, South America, and the Antarctic Peninsula. Purple denotes regions that are lower relative to higher areas like seamounts, depicted in green. Eötvös is the unit of measure for the gravity-based data used to create these maps. Credit: NASA's Scientific Visualization Studio
"The SWOT satellite was a huge jump in our ability to map the seafloor," said David Sandwell, a geophysicist at Scripps Institution of Oceanography who led the mapping research. His team used data from the satellite to identify underwater mountains and hills that previous technologies couldn't detect.
While JPL manages the U.S. component of the project, the mission represents a broad international partnership. NASA's Jet Propulsion Laboratory provided key components including the Ka-band radar interferometer (KaRIn) instrument, while Centre National d'Études Spatiales contributed the satellite platform, ground operations, and several other vital systems.
Mapping the unseen ocean floor
There are better maps of the Moon's surface than of the bottom of Earth's ocean. Researchers have been working for decades to change that. Only about 25% of the seafloor has been directly surveyed using ship-based sonar instruments.
SWOT, which launched in December 2022, wasn't primarily designed to map the ocean floor. Its main purpose is measuring the height of water across Earth's surface, including oceans, lakes, reservoirs, and rivers. However, scientists discovered the satellite could detect subtle gravitational differences caused by underwater features.
"Seafloor mapping is key in both established and emerging economic opportunities, including rare-mineral seabed mining, optimizing shipping routes, hazard detection, and seabed warfare operations," said Nadya Vinogradova Shiffer, head of physical oceanography programs at NASA Headquarters in Washington.
How the technology works
The research team, which includes lead author Yao Yu from Scripps Institution of Oceanography, used a principle of physics to map what lies beneath the waves: underwater features with greater mass exert slightly stronger gravitational pull, creating small, measurable bumps in the sea surface above them.
SWOT's instruments can detect these minute differences with centimeter-level accuracy. The satellite covers approximately 90% of the globe every 21 days, allowing for repeated observations that enhance precision.
Previous satellites could only detect massive underwater mountains over 3,300 feet tall. SWOT can identify seamounts less than half that height, potentially increasing the number of known seamounts from 44,000 to 100,000, according to the researchers. These underwater mountains stick up into the water, influencing deep sea currents. This can concentrate nutrients along their slopes, attracting organisms and creating oases on what would otherwise be barren patches of seafloor.
This advanced mapping capability has revealed seafloor features in regions off Mexico, South America, and the Antarctic Peninsula. In the maps, purple denotes regions that are lower relative to higher areas like seamounts, depicted in green.
Discovering Earth's most abundant landform
One of the most significant findings involves abyssal hills, which the researchers note are the most abundant landform on Earth, covering about 70% of the ocean floor.
"These hills are only a few kilometers wide, which makes them hard to observe from space. We were surprised that SWOT could see them so well," said Yu, an oceanographer at Scripps Institution of Oceanography and lead author on the paper.
Abyssal hills form in parallel bands, like the ridges on a washboard, where tectonic plates spread apart. Their orientation and extent can reveal how tectonic plates have moved over time. Abyssal hills also interact with tides and deep ocean currents in ways that researchers don't fully understand yet.
JPL's role in a global collaboration
The SWOT satellite represents a successful international partnership. While JPL leads the U.S. component from its Pasadena headquarters, the mission includes significant contributions from Centre National d'Études Spatiales, the Canadian Space Agency, and the UK Space Agency.
For the flight system payload, NASA provided several critical components through JPL, including the KaRIn instrument that enables the detailed measurements. Centre National d'Études Spatiales contributed the satellite platform, ground operations, and other essential systems. Additional components came from Canadian and British space agencies.
The path forward
The researchers have extracted nearly all the information on seafloor features they expected to find in the SWOT measurements. Now they're focusing on refining their picture of the ocean floor by calculating the depth of the features they see.
Accurate seafloor maps are also important for an improved understanding of deep-sea currents and tides, which affect life in the abyss, as well as geologic processes like plate tectonics. Underwater mountains called seamounts and other ocean floor features like their smaller cousins, abyssal hills, influence the movement of heat and nutrients in the deep sea and can attract life. The effects of these physical features can even be felt at the surface by the influence they exert on ecosystems that human communities depend on.
The research complements an international effort to map the entire seafloor using ship-based sonar by 2030.
"We won't get the full ship-based mapping done by then," Sandwell acknowledged. "But SWOT will help us fill it in, getting us close to achieving the 2030 objective."