Satellite altimetry
From BAWiki
Definition
A method of satellite remote sensing with the aim of deriving the sea level. Radar pulses are transmitted from a satellite and received again after reflection on the water surface. For the duration of the pulses, the altitude of the satellite is determined above the sea surface. At the same time the satellite's altitude can be calculated from its position via the earth ellipsoid. The difference between the two measures amounts to the height of the sea level above the ellipsoid. This is composed of the so-called geoid height (it represents an average, calm sea) and the so-called marine topography together. For larger areas also inland waters and ice can be observed.