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 ch