NASA maps seafloor from space

NASA-backed researchers are using satellites to map parts of Earth’s seafloor by measuring tiny variations in the height of the ocean surface, a technique that turns gravity signals into clues about what lies below. The work has drawn renewed attention after science-focused social media posts on September 1 highlighted NASA visualizations and recent studies tied to the Surface Water and Ocean Topography, or SWOT, mission. NASA’s Jet Propulsion Laboratory said the method helps scientists detect underwater mountains, abyssal hills and tectonic structures in places where ship-based sonar has not yet gone. NASA says only about a quarter of the global seafloor has been directly surveyed with ships, leaving satellites as a key tool for filling broad gaps. ### How can a satellite “see” the seafloor through miles of ocean? Seafloor features such as seamounts and ridges slightly increase the mass below the water, and that stronger pull creates small bulges on the sea surface above them, NASA said. Deep trenches and troughs do the opposite, producing weaker gravity signatures. By measuring those subtle changes in sea-surface height, scientists can infer the shape of the seafloor beneath. (jpl.nasa.gov) NASA’s Earth Observatory said this approach is part of geodesy, the measurement of Earth’s shape and gravity field. The method does not replace sonar, which can map the bottom directly and in much finer detail, but it gives researchers a global view across remote ocean basins that ships have not covered. ### What is SWOT, and why did it change the maps? (science.nasa.gov) SWOT, launched in December 2022 as a joint mission led by NASA and the French space agency CNES, uses wide-swath radar altimetry to measure sea-surface height with high precision. NASA’s Scientific Visualization Studio said one year of SWOT ocean data was enough to derive a global gravity field approaching 8-kilometer spatial resolution, improving on what researchers could extract from roughly 30 years of older nadir altimetry. (earthobservatory.nasa.gov) A March 2024 NASA JPL release said the new mapping effort produced one of the most detailed seafloor maps yet from space. The agency said the data revealed thousands of small seamounts, individual abyssal hills spanning roughly 200 to 300 kilometers, and tectonic structures hidden beneath sediments and ice. ### What did researchers find in the new maps? NASA visualizations highlighted submarine canyons along the South American continental shelf and ancient spreading ridges concealed beneath ice in the Weddell Sea. (svs.gsfc.nasa.gov) Earlier gravity-based mapping efforts using CryoSat-2, Jason-1 and older missions also uncovered previously uncharted seamounts and fracture zones across remote basins, according to NASA and a 2014 Science paper. (jpl.nasa.gov) Science researchers writing about SWOT said the mission enables detection of more intricate marine tectonic structures at 8-kilometer resolution. That remains coarser than ship sonar, but it expands what scientists can identify over vast areas of ocean floor. ### Why don’t ships just map the whole ocean directly? Ship-based sonar remains the standard for direct bathymetric mapping, but it is slow and expensive to deploy across the global ocean. (swot.jpl.nasa.gov) NASA said only about 25% of the seafloor has been surveyed that way so far, which is why satellite-derived gravity maps remain central to global bathymetry efforts. AGU and other recent research papers say most of the remaining seafloor is still inferred from satellite altimeter-derived gravity data, often using methods first developed in the 1990s and now being refined with machine learning and SWOT observations. (science.org) ### Where can readers see the maps, and what comes next? NASA’s JPL, Earth Observatory and SWOT mission pages host the gravity maps, explanatory graphics and downloadable visualizations tied to the project. (jpl.nasa.gov) NASA has framed the work as ongoing, with SWOT still collecting ocean data that researchers say should improve bathymetric prediction and the study of marine tectonics. Recent papers in Science, AGU journals and Nature-linked data publications show the next phase is less about proving the concept than improving resolution and prediction methods. (agupubs.onlinelibrary.wiley.com) Named participants in that work include NASA, CNES, Scripps Institution of Oceanography and university researchers building updated global bathymetry products from SWOT-derived gravity. (science.org) (jpl.nasa.gov)