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How did the Seasat 1 satellite help scientists study the oceanic geoid?

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Diagram showing the deflection of the vertical from the geoid to the ellipsoid or spheroid, with labeled lines for geoid, spheroid, rock surface, ocean, and geoid height in a geology context. — geoid Deflection of the vertical from the geoid to the spheroid.

Seasat 1, launched in 1978, was the first satellite dedicated to mapping the ocean surface, providing a critical advancement in the study of the oceanic geoid. It utilized an onboard radar altimeter to measure the distance from the satellite's position to the sea surface with a precision of a few centimeters.12

By sampling elevation every three kilometers along its path, Seasat 1 provided average ocean heights for millions of points. Because the unperturbed ocean surface acts as an equipotential surface of Earth's gravitational field, these measurements allowed scientists to visualize the oceanic geoid.13

The data revealed that the ocean surface is warped by seafloor features; for instance, gravitational attraction causes the surface to bulge over seamounts and downwarp over deep-sea trenches. By averaging these elevations, researchers were able to produce global maps that provided direct visual confirmation of the oceanic geoid and helped compute the gravity field of the ocean basins, revealing previously uncharted geological features like ridges and fracture zones.21