Incredibly detailed map of Earth’s seabed created from space

We know surprisingly little about Earth’s deep seabed: only a small percentage has been mapped in detail. There are better maps of the surface of the Moon than of the bottom of Earth’s oceans.

Ships equipped with sonar can plot depth with high accuracy, but navigation time costs money, operates at ship speed, and leaves large gaps between tracks.

Satellites, on the other hand, can frequently observe most of the planet. The Surface Water and Ocean Topography (SWOT) mission, a partnership between NASA and CNES, covers approximately 90% of Earth’s surface waters every 21 days between approximately 78°N and 78°S.

However, until recently, they ignored the small features important to ocean geology and physics.

As part of this ongoing effort, a NASA-backed team recently released one of the most detailed maps of the ocean floor to date. Their new study shows what regular satellite observations can do when combined with careful physics.

How SWOT mapped the seafloor

Using SWOT observations from April 2023 to July 2024, the new maps reveal features of the deep sea that were mostly invisible before.

The satellite maps the height of the ocean in two dimensions using radar interferometry, which allows scientists to see the smallest bumps and troughs.

Underwater ridges and volcanoes contain more mass than the neighboring seafloor. More mass means a slightly stronger pull on Earth’s gravitational field.

This additional traction raises the sea surface above these features by only a few hundredths to a few tenths of an inch (about 0.5 to 7 millimeters). SWOT can measure sea surface height with centimeter accuracy.

Scientists then look for patterns in the “ripples” on the sea surface, as they often lie above the edges and rise up from the seafloor. In this sense, SWOT “reads” the ocean surface to detect what lies beneath.

From height to gravity edges

The team transformed the height data into a map of the vertical gravity gradient. This quantity highlights abrupt changes in gravity, which tend to mark compact boundaries, ridges and bumps.

The approach emphasizes the structure of short wavelengths, so it highlights small features while leaving larger trends in the background.

Over the past three decades, nadir altimetry has mapped marine gravity at resolutions of about 12 to 16 kilometers (7.5 to 9.9 miles), leaving many small features unresolved.

With the new analysis, the global gravity map can detect features up to about 5 miles (≈8 kilometers) in diameter. This jump in resolution turns faint clues into clear signals and fills large swaths of the ocean that have never been surveyed by a modern ship.

Abyssal hills in the depths of the ocean

Abyssal hills cover large areas of the ocean depths. They form when plates separate at mid-ocean ridges and the new crust cools and cracks. In regions mapped by ships, researchers can easily trace their spacing and direction.

With the new global map, scientists can track these hill fields across entire basins and watch their orientations change from region to region.

These alignments record the direction and rate of seafloor spreading over millions of years.

With a clearer view of these models, geologists can refine reconstructions of past plate movements and test how changes in spreading rates have shaped ridges, fracture zones and volcanic chains.

Smaller seamounts and hidden scars

Underwater volcanoes are distinguished by their extra mass which produces powerful and compact gravitational signals. Previous satellites reliably detected seamounts about 1 kilometer (about 0.6 mile) high.

SWOT can detect seamounts less than half that height, in areas where ships have already mapped the bottom and confirm what the satellite detects by gravity.

Since small seamounts far outnumber large ones, the global inventory will expand as this information feeds into seafloor maps. This is important for basic volcanology and for practical tasks such as planning routes for seafloor infrastructure.

Continental margins, where shallow shelves flow into the deep ocean, often carry thick blankets of sediment. These layers can obscure older tectonic structures and river channels.

Models of gravitational gradients now reveal submarine canyons cut into plateaus and hint at buried ridge and fault networks. These signals record how continents stretched, broke apart or collided before sediments hid the evidence.

With a consistent view along many coastlines, researchers can compare margins on different continents and piece together how ocean basins opened and evolved after plates separated.

Mapping the Earth’s seafloor is important

Seafloor roughness shapes deep currents and helps generate internal tides – waves that propagate within the ocean rather than on the surface.

These waves mix water masses, direct heat and carbon, and influence how models simulate climate. When models know where the bottom is rough or smooth, they can represent this mixture more realistically.

Clearer gravity maps also guide safe routes for undersea cables and pipelines, inform work on tsunami and earthquake risks, and make it easier to navigate poorly mapped regions.

Fisheries research also benefits, as seamounts and canyons can concentrate nutrients and marine life, creating productive hotspots.

Ships always fix the depth

Satellite gravity is no substitute for ship sonar. The ships always measure the true depth and provide the points that anchor each bathymetric map. What SWOT provides is the details between the tracks.

This detail directs ships toward high-value targets, whether it’s a steep ridge in a gap or an uncharted canyon that likely conceals complex terrain.

As SWOT collects more repeat passes during its 21-day cycle, the random noise in the maps will decrease and even smaller features will stand out.

Researchers can merge gravity information with existing depth surveys using modern statistical and machine learning tools to improve global bathymetry. This process produces more effective maps for navigation, ocean modeling and risk planning.

Mapping the seabed by gravity

The central idea uses simple physics. The extra mass below pushes gravity above, and gravity lifts the sea surface by a tiny amount.

Measure these heights very precisely, convert them to gravitational gradients, and you get a sharp portrait of the seafloor’s edges and bumps.

With coverage that spans most of the globe and fine horizontal resolution, this first year shows just how far out of reach hidden structures were.

Oceans cover most of our planet, but the bottom remains invisible. By listening to the sea surface and following its slightest tilts, scientists can more completely map the invisible.

The result is a clearer picture of the abyssal hills that trace plate movement, the compact seamounts that expand volcanic records, and the canyon systems that mark the boundary between continents and the deep.

The full study was published in the journal Science.

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