Seafloor Exposed by Navy Satellite

<sup>Satellite map of undersea mountains in the Atlantic. The Puerto Rico Trench, which is nearly as deep as Mt. Everest is high, is the dark line north of Puerto Rico. The Cayman Trench is the dark line south of Cuba.

Image Credit: NOAA/Geosat</sup>

Satellite data collected by the US Navy during the Cold War and now declassified reveal a new, more detailed picture of the ocean floor. The shape of the ocean surface mimics the shape of the ocean bottom below.

Gravity from undersea mountains pulls water towards them and raises the height of the ocean above, much like a magnet hidden under a sheet of paper pulls iron filings towards it. These gravity-induced ocean "hills" rise above the average sea level by as much as 300 feet. These hills rise so gradually that they are not perceptible to ships.

Mapping the ocean floor by satellite is much faster and cheaper than by the earlier method of using sonar from ships. The satellite map shown above was made from data obtained by the Geosat satellite of the National Oceanic and Atmospheric Administration (NOAA). The satellite used laser ranging to measure the height of the ocean below it. It is estimated that to map the ocean floor in the same detail would require ships using state-of-the-art equipment to operate for 125 years and cost several billion dollars. The Geosat satellite took 18 months and cost $80 million.

More Cool Stuff

To learn more about the earth's oceans, go to the Public Connection Web site, an outreach project of Rice University and the Houston Museum of Natural Science. Click on "Welcome to Planet Earth," and then on "Climate" or "Resources":

http://space.rice.edu/hmns/connect.html

For great images and captions suitable for use in the classroom, go to NOAA's Web pages "Exploring the Ocean Basins with Satellite Altimeter Data" and click on "Figures and Captions":

http://www.ngdc.noaa.gov/mgg/announcements/text_predict.HTML

To get more detailed maps and data from NOAA:

http://www.ngdc.noaa.gov/mgg/announcements/announce_predict.html

For information on the earth's major oceans, go to "Ocean Planet: Fact Sheets" from NASA's Goddard Space Flight Center:

http://tutuila.gsfc.nasa.gov/HTML/oceanography_geography.html

For more detailed information on measuring ocean features from earth orbit, go to the NOAA Geosciences Laboratory homepage and click on "Satellite & Ocean Dynamics":

http://gracie.grdl.noaa.gov

Two pages of the NOAA Geosciences Laboratory site have particular relevance to this Observation of the Week -- "Mapping the Southwest Indian Ridge with Geosat" and "Global Sea Level":

http://gracie.grdl.noaa.gov/GEO/eos_paper.html

http://gracie.grdl.noaa.gov/SAT/SAT.html

Geosat data have also been used to map land areas. An excellent example is a map of Greenland derived partially from Geosat data and produced by the National Survey and Cadastre, Denmark:

http://www.kms.min.dk/geodesy/grenland.htm

Check out other observations in the Observation of the Week Archive.