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Seeing the Seafloor Using Sound - Multibeam Sidescan Sonar

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How do you see under the ice? How do you see under the water? Sonar and seismic imaging allow researcher at both poles to look below the surface of the oceans and glacial ice. Using these methods researchers at the poles can map the topography of the Arctic and Antarctic seafloor and the Antarctic continent. Researchers at the poles have been able to use this method to image through other matter.

In Antarctica there are many research teams working aboard Icebreakers like the Research Vessel Icebreaker Nathaniel Palmer. They study the recent tectonic history in the Antarctic Peninsula region and the major Antarctic seas. This research looks at how the Earth's crust is being deformed, destroyed and created at tectonic plate boundaries. To do this, they "see" the ocean floor using instruments that employ sound using a method called sonar. The sonar waves reflected back to the shop from the ocean floor are used to create images of the sea floor, making very detailed maps of surface features. Arctic and Antarctic researchers also examine the layering in Earth's crust below the sea floor, also using sound waves using a method called multichannel seismic imaging. Air canons produce at lower frequencies than sonar; they penetrate the ocean bottom and bounce off internal layers of the crust. As the returning sound waves are detected, they are used to build a picture of features below the sediments that we cannot see directly.

The research that I was involved in was conducted along the Antarctic Peninsula; an area is tectonically active and complex both on the seafloor and in the upper crust. Several plates come together here. New sea floor is being created as, plates are sliding past one another along strike-slip faults, and plates are being destroyed as they plunge into subduction zones. This is occurring in one very active location near Deception Island (an active volcano) the Antarctic Peninsula in an area called the Bransfield Straight. Understanding how the plates interact and what their history is will provide important information about how our Earth's crust changes through time. The detailed maps of geologic structures we are creating will be used to aid future researchers in the area. Scientists using the DSRV ALVIN, a research submarine, will visit parcticularly interesting sites in person by researchers to the area during future voyages.

These sites represent a resource of material. Most are images that you can use to show actual images produced for seismic and sonar data collection methods. There are also graphics showing how the ships are outfitted to collect seismic and sonar data. The GLACIER site is an excellent resource not only for information about how the ocean seafloor is explored. It is also an invaluable resource for Antarctic information and data about all types of research conducted there.

Graphic of horizontal strata made using multichannel seismic data. http://www.ig.utexas.edu/news/bransfield/report3/seismic.gif

Three Sisters formation: sonar seafloor map from the Bransfield Straight Region. http://www.ig.utexas.edu/news/bransfield/report4/sisters.gif

Graphic showing vertical features using seismic data. http://www.ig.utexas.edu/news/bransfield/report4/seismic.gif

Picture of seismic streamer being deployed used for data collection. http://www.ig.utexas.edu/news/bransfield/report2/tail.gif

Graphic of seismic data with explanation of features present. ../../Images/expedition/2_volcseismags.gif

Side Scan Sonar Graphic - showing the working parts of the system. ../../Images/expedition/2_sidescansonar.gif

Glacier Ocean Tools Resource page. Excellent reference showing information about methods of investigating the ocean floor. From sonar to sediment coring. ../../oceans/4_monitoring.html

Resources and Reference Materials
Information about sonar mapping aboard the N.B. Palmer can be found at the TEA web site - tea.rice.edu in Steven Stevenoski's and Kim Giesting's journal pages.

Information about Antarctic seafloor and plates research can be found at the University of Texas Institute for Geophysics web site at www.ig.utexas.edu.

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