Satellite altimetry was developed in the 1960s soon after the flight of artificial satellites became a reality. From the vantage point in space, a radar altimeter is able to measure the shape of the sea surface globally and frequently. Such measurements have a wide range of applications to oceanography, geodesy, and geophysics. The results are often revolutionary. For example, in oceanography; it takes a ship weeks or months to cross the ocean making measurements while the ocean is constantly changing its circulation, temperature, and salinity. Therefore, it is unfeasible to make synoptic observations of the global ocean using in situ instrumentation. The advent of satellite altimetry has given oceanographers a unique tool for mapping the global ocean topography for studying the ocean circulation and its changes with time.