We know more about the surface of the planet Mars than we know about what is at the bottom of Earth's oceans.Until recently, scientists had mapped only about 20 percent of the sea floor.But our knowledge of the deep seas is changing because of information from satellites.Scientists have produced a new map that provides a detailed picture of the oceans.The map is expected to help oceanographers, industry and governments.The new map is two times as detailed as the map made 20 years ago.David Sandwell is a geophysics professor at the Scripps Institution of Oceanography at the University of California.He and other scientists worked on the mapping project.He says they turned to space to look deeper into the ocean. He spoke to VOA on SKYPE."The way we're doing that is to use a satellite altimeter, a radar to map the topography of the ocean surface.Now that seems sort of strange that you'd map the topography of the ocean surface when you really want to get at the sea floor.But, the ocean surface topography has these bumps and dips due to gravitational effects that mimic what's on the sea floor."
