Global observation of the oceans by satellite altimetry entered a new era with the European Space Agency ERS-1 and U.S./French TOPEX/POSEIDON missions, which were launched in July 1991 and August 1992, respectively. For the first time, two altimetric satellites were flying simultaneously. TOPEX/POSEIDON (TP) is an optimized altimetric mission dedicated to the precise observation of the large-scale oceanic circulation. ERS-1 is a multimission satellite. It carries a Synthetic Aperture Radar (SAR), a wind scatterometer, an along-track scanning radiometer and a radar altimeter.