Contact: Eliot Hurwitz FOR IMMEDIATE RELEASE (301) 713-3066 10/23/95
Using satellite sensor data recently declassified by the Navy in combination with data from the European Space Agency, Smith and his colleague, Professor David Sandwell of the Scripps Institution of Oceanography, have generated a computer model of the seafloor in unprecedented detail. The new map, which infers seafloor features from changes in the strength of gravity, provides the first detailed view of ocean floor structures in many remote areas of the Earth.
Marine geologists have been mapping the ocean floors for some time but, because of limited quality and coverage of the available data, they have had to use guesswork. Until now, the most common method of mapping the seafloor has been acoustic echo sounder readings taken by ships; only a small fraction of the sea floor has been charted, and in some remote parts of the oceans there are gaps between charted areas the size of Kansas. Much of the available data is also low tech, and inaccurately navigated. Even using the most advanced technologies available today, it would take over 125 years to chart the ocean basins using acoustic devices on ships.
The newly declassified satellite data have a survey track every three miles, and so scientists can be confident that any feature six miles across will not be missed. Another benefit of mapping the ocean floor via satellite is that the features detected are located with great precision. With this data it may be possible to answer questions like: Is there an uncharted island somewhere where Amelia Earhardt could have landed? Are there uncharted shallow banks that could be rich with marine life and exploitable by commercial fishing? (We already know the answer to that one is Yes.) Are there sedimentary basins that might have petroleum reserves that we haven't mapped yet?
The data used to generate the new map was gathered by the U.S. Navy's GEOSAT spacecraft between March 31, 1985, and October 30, 1986. As the satellite orbited the Earth almost 500 miles up in space, a radar altimeter on board returned readings of the distance from the satellite to the ocean surface accurate to about one inch. The radar waves were reflected by the ocean surface and did not penetrate it, unlike the sound waves of an echosounder, so that the satellite data yield measurements of the shape of the ocean surface, not the ocean floor. However, Smith and his colleagues at NOAA and Scripps have worked out a method for exploring the ocean floors using these data. They first use the satellite data to find tiny changes in the pull of the Earth's gravity field, and then use those gravity anomalies to infer the topography of the ocean floor.
"If I had to choose one thing as being most revolutionary about this map, I would say it is the view it gives us of the fracture zones," said Smith. In the process of seafloor spreading that causes continental drift, scars are made on the ocean floors called fracture zones that record the history of plate motion. These are used to reconstruct the ancient positions of the continents. Such knowledge can be extremely valuable in minerals exploration and in the study of climate change.
The scientific value of these data was anticipated even as the satellite was flying, and many people have worked a long time to get the data declassified. While a senator, Vice President Gore started a group called the Environmental Task Force, to seek answers to this question: are there technologies and data sets which, because of their military value, are classified, but which would have even greater value to the scientific community and the civilian economy if they could be released? This release of data set is one result of this exercise.
Although the work to declassify the data is done, NOAA's work with the data is really only now beginning, as it is now possible to derive data products that can be distributed to scientific, educational and commercial users. The raw data representing the spacecraft's measurement of ocean surface heights is now available from NOAA's National Ocean Data Center in Washington, D.C., on a set of 4 CD ROM discs. Over the coming months, new products, such as marine gravity fields and predicted sea floor topography, will be made available. A picture of what kinds of products will be coming can be had on the Internet at http://www.ngdc.noaa.gov/mgg/announcements/announce_predict.html. Color prints of the draft version of the new world gravity map will be available to qualified news media from the contact above.