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How do satellite measurements of the ocean surface reveal seamounts and deep-sea trenches?

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World map highlighting major features of the ocean basins, including trenches, ridges, basins, and plateaus labeled throughout the Pacific, Atlantic, Indian, Southern, and Arctic Oceans. Continents are shown with shaded terrain, and prominent undersea features such as the Mid-Atlantic Ridge, Mariana Trench, and Kerguelen Plateau are marked across the map. — ocean basin Major features of the ocean basins.

Satellites equipped with radar altimeters reveal seafloor topography by measuring the distance between the satellite and the ocean surface with high precision. Because the gravity field at the surface is a sensitive indicator of marine topography, the shape of the sea surface is warped by the gravitational attraction of features on the ocean floor.1

These measurements reveal seafloor features in the following ways:

Seamounts: Massive seamounts exert a gravitational pull that causes the ocean surface to bulge upward over them.1
Deep-sea trenches: Conversely, the ocean surface exhibits a downwarp (a depression) over deep-sea trenches due to the local gravity field.1

By analyzing these surface variations, scientists can compute the gravity field to create detailed gravity maps. This method provides comprehensive coverage of the ocean basin that is often more complete than what can be achieved through ship-based echo soundings, allowing researchers to identify previously uncharted features such as ridges and fracture zones.1