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Sunday, February 17, 2013

Mapping ocean depth because underwater mountains attract water.

When scientist get ahold of even the tiniest information, they can deploy it to great effect! Steve 

Satellite Altimetry
According to the laws of physics, the surface of the ocean is an "equipotential surface" of the earth's gravity field. (Lets ignore waves, winds, tides and currents for the moment.) Basically this means that if one could place balls everywhere on the surface of the ocean, none of the balls would roll down hill because they are all on the same "level". To a first approximation, this equipotential surface of the earth is a sphere. However because the earth is rotating, the equipotential ocean surface is more nearly matched by an ellipsoid of revolution where the polar diameter is 43 km less than the equatorial diameter. While this ellipsoidal shape fits the earth remarkably well, the actual ocean surface deviates by up to 100 meters from this ideal ellipsoid. These bumps and dips in the ocean surface are caused by minute variations in the earth's gravitational field. For example the extra gravitational attraction due to a massive mountain on the ocean floor attracts water toward it causing a local bump in the ocean surface; a typical undersea volcano is 2000 m tall and has a radius of about 20 km. This bump cannot be seen with the naked eye because the slope of the ocean surface is very low.
Watch the resulting 2 hour TV special (USA only, or if you have a VPN).