Computed and observed ocean topography: A comparison

Abstract

This paper presents determinations of ocean topography using spacecraft altimeter techniques. The first direct spacecraft observations of sea-surface topography were made in late 1973 during the Skylab mission. Comparisons of the topography derived from the altimeter data with the ‘computed’ topography based upon the Goddard Space Flight Center Earth Gravity Model, GEM-8, derived from satellite tracking data and surface gravity data show differences of a few meters. With the presently orbiting altimeter system on the Geos-3 spacecraft, relative variations over a few hundred kilometers along the orbital track can now be detected to a few decimeters. Numerous short-wavelength features which reflect large variations of the ocean floor have been observed to a relative precision of a meter or better with Geos-3. For example, the Blake-Bahama Basin off the coast of Florida is about 4000 m lower than the continental shelf. The sea surface of the basin, as measured by the Geos-3 altimeter, is about 8 m lower than that of the continental shelf. Further, a height change of over 20 m has been measured over the Puerto Rican Trench relative to the height of the mean sea level at Puerto Rico. Preliminary results of on-going studies indicate that geostrophic height variations, for example, due to ocean currents (the Gulf Stream has an expected variation of around 1.5 m over 100 km) will be detectable using spaceborne altimeters.