SWOT sharpens seafloor focus
At present, ship-mounted soundings have surveyed about 25% of the seafloor. For the other 75%, the only information comes, indirectly, from satellite altimeters that measure the detailed shape of the sea surface. This shape provides information about the variations in gravity from undersea topography, so altimeter data provide most of the seafloor topography shown in common map programs such as Google Earth.
Yao Yu, a postdoctoral researcher at Scripps Institution of Oceanography at UC San Diego, and colleagues revealed the results produced by the Surface Water and Ocean Topography (SWOT) radar altimeter in a study published Dec. 13 in the journal Science.
The team used SWOT data to transform what may have resembled blurry blobs into discernible seamounts, ridges and troughs. They compared SWOT data to 30 years' worth of data from traditional altimetry that only measured in one dimension rather than in the swaths that SWOT measures.
"In this gravity map made from merely one year of SWOT data, we can see individual abyssal hills, along with thousands of small uncharted seamounts and previously hidden tectonic structures buried underneath sediments and ice," said Yu. "This map will help us to answer some fundamental questions in tectonics and deep ocean mixing."
A multipurpose instrument package, SWOT can also resolve subtle nuances of ocean circulation by measuring the topography of the ocean surface, which is ever-changing. Those data show what gravity's pull is like across given swaths of ocean, revealing phenomena such as internal waves the way a medical imaging device can view internal organs of the body.
The instrument-packed satellite, launched on Dec. 16, 2022, is a joint endeavor by NASA's Jet Propulsion Laboratory (JPL) and its French counterpart CNES (Centre National D'Etudes Spatiales), with contributions by the Canadian and UK Space Agencies. Scripps Oceanography joined six other research institutions leading ocean campaigns based on SWOT data.
Co-authors of the study include geophysicist David Sandwell from Scripps Oceanography and Gerald Dibarboure from the Centre National d'Etudes Spatiales in Toulouse, France.
The ultimate resolution of marine gravity from SWOT will provide sharpness to the level of at least eight kilometers (five miles). That is still not as detailed as the 200-meter (650-foot) scale resolution obtained from ship-mounted instruments but will cover the three-quarters of the seafloor not mapped by ships.
"We haven't reached the plateau yet," said Yu. "With more data accumulated we will be able to study changes in the marine gravity field, such as from undersea volcano eruptions."
Sandwell, already the originator of most Google Earth seafloor imagery, is now leading a global effort with the Technical University of Denmark and the U.S. National Geospatial Intelligence Agency, the Naval Research Laboratory, NOAA, and the French agency Collecte Localisation Satellites to make an improved global seafloor map using SWOT marine gravity combined with all publicly available ship soundings.
Research Report:Abyssal marine tectonics from the SWOT mission
Related Links
Surface Water and Ocean Topography (SWOT)
Water News - Science, Technology and Politics
