One year of SWOT satellite data has sharpened a global view of gravity over the oceans.
The map approaches a spatial resolution of about eight kilometres.
It reveals abyssal hills and thousands of small seamounts hidden beneath the surface.
A satellite designed to measure the height of water has produced a more detailed global view of structures on the seafloor. NASA and France's CNES used one year of data from the Surface Water and Ocean Topography mission, known as SWOT, to map small changes in the ocean surface caused by the gravity of underwater terrain.
Ships have directly mapped only about a quarter of the world's seafloor with sonar. The gaps are too large to fill quickly by vessel alone. Satellite altimetry offers an indirect route. A seamount adds mass and slightly strengthens local gravity, drawing water into a broad bulge. SWOT's radar measures those tiny variations in sea-surface height, from which researchers infer the gravity field and the likely shape below.
SWOT observes a wide swath on both sides of its ground track rather than measuring only the line directly beneath the spacecraft. That coverage allowed the team to approach roughly eight-kilometre spatial resolution after a year, exposing more detail than more than three decades of conventional nadir altimetry.
The resulting gravity map shows individual abyssal hills, which are low parallel ridges created as tectonic plates spread, and thousands of relatively small seamounts. Researchers expect the data to reveal around 50,000 previously unknown seamounts about one kilometre tall. Such features influence deep-ocean circulation and provide clues to plate movement and volcanic history.
This is not a photograph or a direct depth chart. Gravity must be converted into an estimate of seafloor structure, and sediment or complex geology can make that relationship uncertain. Ship-based sonar remains necessary for navigation-grade bathymetry and for verifying specific sites.
The immediate value of the satellite map is in deciding where ships should look. A global indirect survey can identify ridges, faults and candidate seamounts, allowing scarce sonar missions to target the most informative areas. SWOT has therefore turned repeated measurements of the ocean's surface into a practical guide to the largely unmapped world beneath it.
Sources
NASA JPL: Next-generation water satellite maps seafloor from space
NASA JPL: SWOT vertical gravity gradient