Gaining a better understanding of the surface of the oceans means gaining a better understanding of marine dynamics, the climate and changes in sea level. Long hampered by the technical limitations of satellites, this mapping is now being refined thanks to a new space technology that is revolutionising the standards of ocean observation on a global scale.
By Laurie Henry
Cover photo: Example of level 3 composite mapping (unit cm) obtained in January 2024 with SWOT © CNES, CLS
Knowing precisely how deep the ocean is is essential for measuring sea level rise, modelling ocean currents and mapping the seabed. Until recently, these measurements relied on vertically aimed satellites, which are limited in their ability to distinguish fine details of the seafloor. Since December 2022, the SWOT satellite has been breaking through this technical barrier thanks to its wide-beam altimetry system. Equipped with the KaRIn instrument, it offers unprecedented two-dimensional observations of water surface height. Researchers from the DTU Space at the Technical University of Denmark have published an in-depth evaluation of this capability in Geophysical Research Letters, comparing SWOT with Sentinel-3 satellites. Their objective is to determine to what extent SWOT improves the mapping of static ocean topography.
Disruptive technology for an age-old challenge
Traditionally, altimetric satellites only measure the height of the sea directly above their trajectory, point by point. The satellites mainly orbit from north to south, following quasi-polar trajectories. With each orbit, they collect a narrow line of data (a few kilometres wide), several hundred kilometres apart from the next. As a result, the measurements between two successive passes are very dense in the north-south direction, but spaced out in the east-west direction, where the resolution is much lower. This limitation prevents the detection of small undersea features, such as seamounts or fine undulations of the surface related to the geology of the seabed.