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What It Monitors
The ocean's surface is considered to be "equipotential," due to the gravity exerted by forces of varying heights and levels of magnetism at the floor deep below. According to the National Geophysical Data Center, this means that if balls were floated on the surface all across the globe, they would be at the same basic height. The variances, which can be monitored via satellite by radar altimeter, register as small bumps or dips that tend to correspond with large mountains or valleys deep below the sea.
How It Works
The radar altimeter mounted on various satellites records the exact distances to every point of longitude and latitude on a map of the ocean. Another key measurement is the exact distance of a satellite from Earth's ellipsoid, or equipotential base. This enables the collection of data on the oceans' bulging and dipping, which has given scientists the ability to chart the ocean floor and monitor changes in current, wave height, depth, temperature and even salt content.
For the Public Good
According to the European Space Agency, radar altimeters were first mounted to the United States' Skylab and GEOS-3 satellites before they were launched in 1975; however, it wasn't until 1978, with the launch of Seasat satellite, that data began to be systematically recorded in the form of color-coded photos showing the range of ocean depths and more accurate views of the ocean floor. By the mid-1980s, a range of satellites launched by several countries were equipped with radar altimetry equipment.
Easy Online Monitoring
In 2011 altimetry data is accumulated by so many satellites in various points of orbit that depth and wave height data can be obtained almost in real time to within 1 inch of accuracy. At Mercator Ocean, for example, not just current data but one- and two-week forecasts are available using data from several satellite altimeters. Current animations are also available for free at the website, as well as information about salinity and temperature change.