The Geoid from Satellite Altimetry

Satellite altimetry has revolutionized our knowledge of the shorter wavelengths of the geoid, let us say 50 to 1000 km wavelength, because it provides global coverage with uniform accuracy during a measurement campaign of one to three years. Satellite orbit perturbation techniques provide the long wavelengths of the geoid, and now altimetry is also used as a tracking data type to improve those long wavelengths. A radar altimeter measures the two way travel time of a pulse emitted by an antenna onboard the satellite, scattered back by the ocean surface, and received by the same antenna; it also measures the time history of the backscattered energy. From the point of view of the geodetic user of the data, the key issue with tides is whether or not the satellite’s sampling has aliased tidal components into very long periods, indistinguishable from the geoid.