Earthshaking News From Old Spy Pix

OLD SATELLITE PHOTOS THAT had seemingly given up all their secrets are yielding new information at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

JPL geologists Robert Crippen and Ronald Blom devised a way to spot ground shifts by superimposing two satellite photos taken at different times. A team led by Paul E. Stolorz programmed the concept into a Cray T3D supercomputer and used statistical tricks to improve the resolution and spot ground movements as small as one meter.

The computer works with 100-by-100 blocks of pixels taken from larger images. If a block from the new image has to be shifted to line up with the old one, the computer records this as motion. The process is repeated thousands of times. The image here, which required 24 hours of processing on the Cray, shows dislocations in the Mojave Desert from the Landers earthquake of 1992. The color compass in the corner indicates the direction of movement. The added black lines depict known faults.

Now, the JPL team is looking for sand-dune motion on Mars. Next, it will examine Europa, a moon of Jupiter, for signs of motion that would hint at liquid water beneath its ice crust. Stolorz says a 3-D version might detect tumor growth in X-ray images.

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