Geographers, video game designers, and anyone else who needs a detailed three-dimensional map of Earth's mountains, valleys, and other land areas now have one available. Technicians at the U.S. space agency NASA and the Defense Department have finished converting high altitude space shuttle radar images of our planet into full-color digital topographical maps that far exceed the detail and accuracy of previous images.
The space shuttle mission bounced radar signals off Earth's surface for 10 days in 2000, but it has taken technicians four years working with supercomputers to make commercially useful three-dimensional maps of them. The last land areas to be completed are Australia, New Zealand, and islands in the Pacific Ocean.
NASA scientist Michael Kobrick says two radars aboard the space shuttle collected 12 terabytes of raw elevation data. That is enough digital information to fill 15 million compact disks. "So we had to put those together to make a coherent three-dimensional map. It's not just like making a photograph like we do a lot from space, from satellites. It's much more painstaking. You have to be much more careful to get it exactly right because people's lives in some cases depend on it," he says.
The space shuttle orbited Earth in a criss-cross pattern, covering 80 percent of the landmass. Each time it circled, both radars emitted 1,500 signals over a 250-kilometer-wide swath. The time it took for the pulses to bounce back was a measure of the distance between the instruments and the Earth's surface. The two radars were spaced 60 meters apart to provide a three-dimensional view.
NASA says the maps reveal for the first time large, detailed regions of Earth's topography never before gathered by explorers and surveyors or obscured by clouds to satellite cameras.
Mr. Kobrick says the data will benefit scientists, engineers, government agencies, and the general public with a wide array of uses.
"Siting [locating] communications towers is a lot easier to do if you have a digital elevation map. It can be used in airplanes. There is no technical reason now why a pilot can't have in the cockpit a virtual display, almost like a video game display, of what it [the ground] should look like out the window just in case he can't see out the window because of darkness and bad weather," he says.
In fact, Mr. Kobrick says a video game developer uses the data so his computer flight simulator program can display actual terrain. "It's surprising how much application there is. People are coming up with uses for these kind of data that I frankly never even thought of before," he says.
The images show details of Earth's topography down to about 100 meters in size, the length of a football field. Mr. Kobrick says in time NASA would like to improve the resolution so the maps could show details as small as an automobile. The goal is to have a satellite return full-time radar data to show changes in Earth's elevations over time.
"What we have here is a snapshot of the planet taken in that one-week interval early in 2000. What we can do now is compare those data with data we might acquire later from all kinds of satellites, especially if we have an imaging radar in orbit again and look for changes. In fact, we can actually detect changes in the surface of the Earth to something like the thickness of a paperback book, a few centimeters. This is really important because we believe that these kind of ground motions over a large area are possibly precursors to earthquakes, volcanic eruptions. So that's a very exciting future possibility for this kind of technique," he says.
The new topographical maps can be purchased on compact discs from the U.S. Geological Survey.