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==Applications==
Ocean surface topography is used to map [[ocean current]]s, which move around the ocean's "hills" and "valleys" in predictable ways. A clockwise sense of rotation is found around "hills" in the northern hemisphere and "valleys" in the southern hemisphere. This is because of the [[Coriolis effect]]. Conversely, a counterclockwise sense of rotation is found around "valleys" in the northern hemisphere and "hills" in the southern hemisphere.<ref>{{cite web | url = http://topex-www.jpl.nasa.gov/education/tutorial2.html | title = Ocean Surface Topography from Space | publisher = NASA/JPL}}</ref>
Ocean surface topography is also used to understand how the ocean moves heat around the globe, a critical component of Earth's [[climate]], and for monitoring changes in global [[sea level rise|sea level]]. The sea surface height (SSH)<ref>{{cite web|url=http://www.libraryofoceanography.com/papers.php?pgnum=14&sortBy=title |title=Statistics of spatial-temporal variations of sea surface height based on Topex altimeter measurements | publisher=NASA }} [[Roman Glazman]], A. Fabrikant, A.M. Greysukh, 1996</ref> is calculated through altimetry satellites, which determine the distance from the satellite to a target surface by measuring the satellite-to-surface round-trip time of a radar pulse.<ref>Chelton, D.B., J.C. Ries, B.J. Haines, L.L. Fu, P.S. Callahan, Satellite Altimetry, Satellite altimetry and Earth sciences, L.L. Fu and A. Cazenave Ed., Academic Press, 2001.</ref> The satellites then measure the distance between their orbit altitude and the surface of the water. Due to the differing depths of the ocean, an approximation is made. This is called the Arbitrary Reference Surface. Arbitrary Reference Surface is an estimated surface that is calculated to factor in the shape of the Earth. The general shape of the earth is spherical, but flattened out at the [[Polar regions of Earth|North and South Pole]]. This approximated surface is called the reference ellipsoid. This enables data to be taken precisely due to the uniform surface level. The satellite’s altitude then has to be calculated with respect to the reference ellipsoid. It is calculated using the orbital parameters of the satellite and various positioning instruments. The sea surface height is then the difference between the satellite’s altitude relative to the reference ellipsoid and the altimeter range. The satellite sends microwave pulses to the ocean surface. The travel time of the pulses ascending to the oceans surface and back provides data of the sea surface height.
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