Seasat is the only dedicated, multisensor oceanographic satellite to have ever flown. Although the mission lasted for only 3 months in 1978, it returned an enormous harvest of unique and valuable data that are still in the early stages o f analysis. Its sensor complement included a scatterometer for surface winds, a passive microwave radiometer for sea surface thermal measurements, a synthetic aperture radar system for ocean surface imaging, and the radar altimeter. The altimeter provides information on significant wave height, surface wind speed, and above all, the topography of the sea surface. This topography is of prime interest to ocean circulation studies because its horizontal gradient, after removal of the geoidal signal, is proportional to the surface geostrophic current, the principal circulation component.