ESS15_LEC4F10_Bathymetry2_2perpage

ESS15_LEC4F10_Bathymetry2_2perpage - Introduction to...

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1 Plumbago, wikimedia commons, C C A S-A 3.0 Introduction to Oceanography Lecture 4: Bathymetry and Margins Introduction to Oceanography •Reading: Chapter 3. •Check lab exercise key outside 3820 Geology. •Be on time for first lab quiz next week! •Check website for lab readings & extra credit seminars. Anak Krakatau, Indonesia, NASA image, Public Domain Atafu Atoll, Tokelau, NASA image, Public Domain ASUCLA Note taker needed 308 Westwood Plaza
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2 The Big Picture: Continents vs. Ocean Basins Plumbago, wikimedia commons, C C A S-A 3.0 The Big Picture: Bimodal Distribution -10000 -8000 -6000 -4000 -2000 0 2000 4000 6000 8000 10000 0 0.01 0.02 0.03 0.04 0.05 Elevation (meters) Fraction of Earth's surface area Histogram of elevations on Earth Ocean Land Figure E. Schauble based on ETOPO5 data (NOAA), as sampled by S.L. Goldstein and S. Hemming, Columbia U. Bin heights are 100m.
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3 Multibeam Sonar Sound waves are blasted from the ship, and echoes are recorded. The distance to the seafloor is determined from the time between making the sound and the echo: d ! (sound speed)•(time delay)/2 High spatial resolution, mapping a small area (under ship) Explorer ridge west of Vancouver Island, NOAA, www.photolib.noaa.gov/ bigs/expl1571.jpg, Public Domain. USNS Bowditch, http://www.navy.mil/ view_single.asp?id=2767, Public Domain Satellite radar mapping (gravity) Satellites (like TOPEX-Poseidon and Jason-1&2) can measure their distance from the sea surface. Knowing this distance and the orbit of the satellite, we can determine the topography (shape) of the ocean surface. Any extra mass on the seafloor will exert extra gravity on the ocean, causing a “hump” in the sea surface. Thus it is possible to extract the seafloor topography Great spatial coverage, lower resolution & precision (far away). Painting of JASON-2, http://sealevel.jpl.nasa.gov/mission/ images/OSTM-06.jpg, Public Domain Geoid Geoid Modified by E. Schauble from original by MesserWoland, Wikimedia Commons, http://en.wikipedia.org/wiki/ File:Geoida.svg, CC A S-A 3.0
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4 What is Buoyancy? Any object in a fluid will be pushed up as the fluid tries to fill in the space taken up by the object. At rest, a buoyant object will sit so that the mass of fluid it displaces equals the mass of the object.
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