“Mapping the seafloor isn’t the SWOT mission’s primary purpose,” says the JPL, and yet the Surface Water and Ocean Topography (SWOT) satellite is being used for more than measuring sea surface height: those ocean surface topography measurements can be used to infer features on the seafloor. NASA Earth Observatory:
Because geologic features like seamounts and abyssal hills have more mass than their surroundings, they exert a slightly stronger gravitational pull that creates small, measurable bumps in the sea surface above them. These subtle gravity signatures help researchers predict the kind of seafloor feature that produced them.
[…] Through repeated observations, the satellite is sensitive enough to pick up these minute differences, with centimeter-level accuracy, in sea surface height caused by the features below. David Sandwell, a geophysicist at Scripps Institution of Oceanography, and his colleagues used a year’s worth of SWOT data to focus on seamounts, abyssal hills, and underwater continental margins, where continental crust meets oceanic crust.
[…] Areas of decreased gravity (purple) are affiliated with depressions on the seafloor, while areas of increased gravity (green) indicate the locations of more massive, elevated features.
Only about a quarter of the seafloor has been mapped with traditional sonar methods, so you can see how a gap is being filled here. Next up is calculating the depth of the features being detected through this method.