Satellites are unable to penetrate into the depths of the ocean. Yet scientists are able to combine several new technologies to infer the depth of the ocean.
The shape of the earth is not a perfect sphere, but an oblate spheroid. There are bumps on the surface of that ellipsoid that are too small to detect with the human eye, but are caused by the topography of the ocean floor. Therefore a sea mount will cause a bulge on the surface of the ocean, many miles above the actual sea mount.
Using data from the European Space Agency's ERS-1 in combination with recently declassified Navy Geosat altimetry data, scientists have begun to create maps of the ocean floor. Scientists measure the height of the satellite above the earth's ellipsoid (i.e. if the surface of the ocean were perfectly flat). The satellite measures the height above the ocean surface by sending out a pulse and timing its return to the satellite. The difference between the two is the height of the ocean surface at a given location.
The scientists rely on many years worth of data to remove the effects of tides, waves, and other sources of incorrect data. The data from the satellite are also compared to measurements from ships.
The data will be used for sea floor depth predictions, large-scale navigation, planning research expeditions that study the bottom and studies in: plate tectonics, undersea volcanoes, petroleum exploration, and the structure of the oceanic crust.
For more technical information go to the related WWW pages at NOAA.