It is sometimes said that the ocean floor is less known than the surface of the Moon.
In fact, today, barely a quarter of the seabed has been observed with sonar by ships, the most precise means of knowing the depth of the water and the relief of the bottom.
These precise measurements were supplemented by calculations using surface topography measurements made by altimetric satellites such as Sentinel-6 Michael Freilich and its equivalents. But these measurements were only made just below the satellite and detection and calculation was complicated for underwater reliefs with steep slopes.
Even though a satellite’s instruments cannot “see” underwater, or at least not more than a few meters in clear water for some of them (like Spot/Pléiades , Sentinel-2 or IceSat-2), the relief of the water surface partly reflects that of the bottom.
Measuring this “topography” of the surface therefore makes it possible to deduce that of the bottom. The KaRIn instrument on board the Franco-American satellite of CNES and NASA,
SWOT, also called Surface Water Ocean Topography measures this topography of the surface in high resolution with very good precision and under a swath of 120 km, unlike previous altimetric satellites.
The SWOT mission brings together two communities focused on a better understanding of the world’s oceans and its terrestrial surface waters. U.S. and French oceanographers and hydrologists and international partners have joined forces to develop this satellite mission to make the first global survey of Earth’s surface water, observe the fine details of the ocean’s surface topography, and measure how water bodies change over time.
The red dots on this map of a 500 km by 1000 km area west of the Peruvian coast in the Pacific Ocean are seamounts. This image is derived from a processing of SWOT measurements of ocean surface topography, measurements that reflect the relief of the seabed. The two shown by the arrows, for example, are mounts about 1000 m high that were unknown.
SWOT will thus allow the discovery of thousands of other seamounts previously unknown.
Today, approximately 44,000 seamounts of 1000 m altitude from the ocean floor are known. Based on a year of data acquired by the mission, a team from the Scripps Institution of Oceanography estimates that this number will easily double, perhaps reaching 100,000 thanks to future data. Other details of the ocean floor are also to be discovered: complex reliefs on either side of the oceanic ridges, flow channels in the continental slope, etc.
This knowledge of the relief of the seabed should, in the long term, make it possible to facilitate underwater exploration, and even make navigation on the high seas more secure. It could also make it possible to locate and better predict future eruptions, thanks to a better knowledge of tectonic plates and their movements.
Knowledge of the relief of the ocean floor is also useful for understanding the circulation of water in the oceans. Indeed, underwater mountain ranges can have an effect on currents, causing them to dive deeper. This phenomenon, important for the climate, is essential to understand in order to better characterize the role of the oceans in the context of climate change.
The acquisition of additional data in the coming years will further improve the resolution of the relief of the seabed. However, measurements made by dedicated vessels will remain essential to specify the relationship between the surface and the ocean floor.
These measurements, combined with satellite measurements and with the help of analysis methods based on artificial intelligence, will considerably improve knowledge of the ocean floor, particularly in oceans far from any land where few in-situ measurements have been carried out.
The SWOT mission data can be found on the AVISO platform for oceanography and hydroweb.next for hydrology.
