NASA's Earth Observing SystemThe Earth Observing System (EOS) - the principal component of NASA's Mission to Planet Earth - will provide a major comprehensive global observing system that will offer insights into the natural processes that govern our Earth as well as the possible changes that may occur in the atmosphere, on the land, and in the oceans as a result of human activities. Visit the most important component of the Mission To Planet Earth research program.

This is an example of the newest measurements of the sea surface topography. Ocean topography is a measure of sea level relative to the Earth's geoid (a surface on which the gravity field is uniform). Oceanographers use ocean topography maps to calculate the speed and direction of ocean currents in much the same way that meteorologists use maps of atmospheric pressure to calculatethe speed and direction of winds.

This image was produced from preliminary data from the joint U.S.-France TOPEX/Poseidon radar altimeter, a satellite instrument that uses radar to make precise measurements of ocean surface heights.

In this image, the maximum sea level (shown in white) is located in the western Pacific Ocean and the minimum sea level (shown in blue and purple) is around Antarctica. In the northern hemisphere, ocean currents flow clockwise around areas of high sea level, and counterclockwise around areas of low sea level. (This phenomenon is reversed in the southern hemisphere.) Although this image is derived from only 10 days of TOPEX/Poseidon data, it reveals most of the ocean circulation systems that have been identified by shipboard observations collected over the past 100 years, clearly demonstrating the utility of acquiring Earth system data from orbiting instruments.