Jan28_09_Margins_and_Basins

Jan28_09_Margins_and_Basins - Continental Margins and Ocean...

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Continental Margins and Ocean Basins Seafloor features result from a combination of tectonic activity and the processes of erosion and deposition.
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The Ocean Floor Is Mapped by Bathymetry The discovery and study of ocean floor contours is called Bathymetry. (left) An illustration from the Challenger Report (1880). Seamen are handing the steam winch used to lower a weight on the end of a line to the seabed to find ocean depth.
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Bathymetry: The Study of Ocean Floor Contours How did early scientists study the ocean floor? Early bathymetric studies were often performed using a weighted line to measure the depth of the ocean floor. Advances in Bathymetry Echo sounding Multibeam Systems Satellite Altimetry
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Echo Sounders Bounce Sound off the Seabed Echo sounding is a method of measuring seafloor depth using powerful sound pulses. The accuracy of an echo sounder can be affected by water conditions and bottom contours. The pulses of sound energy, or “pings,” from the sounder spread out in a narrow cone as they travel from the ship. When depth is great, the sounds reflect from a large area of seabed. Because the first sound of the returning echo is used to sense depth, measurements over deep depressions are often inaccurate.
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Multibeam Systems Combine Many Echo Sounders Multibeam systems can provide more accurate measurements than echo sounders do. Multibeam systems collect data from as many as 121 beams to measure the contours of the ocean floor.
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Satellites Can Be Used to Map Seabed Contours Satellite altimetry measures the sea surface height from orbit. Satellites can bounce 1,000 pulses of radar energy off the ocean surface every second. (right) Geosat, a U.S. Navy satellite operated from 1985 through 1990, provided measurements of sea surface height from orbit. Moving above the ocean surface at 7 kilometers (4 miles) a second, Geosat bounced 1,000 pulses of radar energy off the ocean every second. Height accuracy was within 0.03 meters (1 inch)! (below) With the use of satellite altimetry, sea surface levels can be measured more accurately, showing sea surface distortion. Distortion of the sea surface above a seabed feature occurs when the extra gravitational attraction of the feature “pulls” water toward it from the sides, forming a mound of water over itself.
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This view of the complex system of ridges, trenches, and fracture zones on the south Atlantic seafloor east of the tips of South America and Antarctica’s Palmer Peninsula was derived in large part from Geosat data declassified by the U.S. Navy in 1995.
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Cross section of the Atlantic ocean basin and the continental United States, showing the range of elevations. The vertical exaggeration is 100:1. Although ocean depth
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This note was uploaded on 10/07/2011 for the course OCS 1005 taught by Professor Condrey during the Spring '08 term at LSU.

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Jan28_09_Margins_and_Basins - Continental Margins and Ocean...

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