© 2002 Brooks/Cole, a division of Thomson Learning, Inc. BATHYMETRY New technology, such as this bathyscaphe, allows scientists to study deep-ocean basins.

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. 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 called a lead line to measure the depth of the ocean floor (a weighted line is lowered into the ocean until it touches the ocean floor).

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. Bathymetry: The Study of Ocean Floor Contours Advances in Bathymetry  Echo sounding  Multibeam Systems  Satellite Altimetry

Echo sounding is a method of measuring seafloor depth using powerful sound pulses. Sound waves are sent from a device toward the ocean floor, bounce off the ocean floor, and travel back to the device. Distance to the ocean floor can be calculated using the speed of sound in water and the time it takes for the sound to be reflected. Echo sounder –Device that sends sound waves down to the ocean floor and times how long it takes to return. Bathymetry: The Study of Ocean Floor Contours

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. Bathymetry: The Study of Ocean Floor Contours

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. Bathymetry: The Study of Ocean Floor Contours Multibeam systems can provide more accurate measurements than echo sounders do. Ships send out many sound beams to collect data on a wide swath of the seafloor, rather than a single line. Multibeam systems collect data from as many as 121 beams to measure the contours of the ocean floor. Also called side-scan sonar

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. Bathymetry: The Study of Ocean Floor Contours

Practice Using Reflected Waves to Measure Ocean Depth –Time for signal to reach the bottom x 1486 m/s = depth –Graph horizontal distance vs. depth –Connect the dots Finding Ocean Depth –Divide time in half –Multiply answer x 1454 m/s = depth –Graph station (distance) vs depth –Answer questions

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. Bathymetry: The Study of Ocean Floor Contours Satellite altimetry measures the sea surface height from satellites in orbit. Satellites can bounce 1,000 pulses of radar energy off the ocean surface every second. Similar to sonar, but using radar waves instead of sound waves

Satellites such as the Topex/Poseidon satellite use radar to map features of the ocean floor. The distance to the water’s surface is calculated using the speed of light and the time it takes for the signal to travel to Earth and back

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. Bathymetry: The Study of Ocean Floor Contours Why Satellite Altimetry works: Higher elevations, like mountains, have more mass so their gravity attracts a water bulge up to 30m high. Troughs & trenches can form depressions up to 60m deep.

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. Bathymetry: The Study of Ocean Floor Contours (above) With the use of satellite altimetry, sea surface levels can be measured more accurately, showing sea surface distortion.

© 2002 Brooks/Cole, a division of Thomson Learning, Inc. A typical cross section of the Atlantic ocean basin. The Topography of Ocean Floors