Radar Altimeter

A radar altimeter is a satellite instrument that measures the height of the sea surface by timing the round trip of a microwave pulse reflected from the ocean. Combined with precise orbit determination, it yields sea surface height to a few centimeters: TOPEX/Poseidon achieved about 3.3 cm accuracy from a 1,330 km orbit. Corrections for ionospheric, wet and dry tropospheric delay, and sea-state bias are applied. Because seamounts add gravitational pull that bulges the sea surface, altimeter data yields gravity-derived bathymetry over unsurveyed ocean, the basis of global grids that fill the gaps between ship tracks in GEBCO.