David Sandwell on Seeing Plate Tectonics Under the Oceans

David Sandwell uses satellites to make accurate measurements of the shape of the ocean surface.  He explains how this enabled him to create a global map of the topography on the sea-floor.  This revealed the global extent of classic plate-tectonic features, such as spreading ridges and transform faults, but also intriguing new features we still do not understand.
David Sandwell is a Professor at Scripps Institution of Oceanography at the University of California San Diego.