Scientists at the Jet Propulsion Laboratory realized that under certain circumstances SAR images could be combined to produce derivative images called interferograms. SAR images show how the surface would look to a pair of radar-sensitive eyes. An interferogram shows how much the surface moved during the time interval between SAR images — with millimeter-scale precision (1 millimeter is less than one-sixteenth of an inch).

With InSAR (interferometric synthetic-aperture radar), scientists can create snapshots of surface deformation without ever trudging to a mountaintop or across a continent. A new branch of geodesy was born.

A remarkable demonstration of InSAR's capability came in 1993 when several French scientists produced an interferogram from ERS-1 images showing in glorious detail the pattern of surface disruption caused by the 1992 magnitude 7.3 Landers, California, earthquake. In the decades prior, geologists had measured fault scarps, geodesists had surveyed nearby benchmarks, and modelers had calculated how the Earth might move during a major earthquake. For the first time ever all could marvel at a "picture" of what actually happened. It was a snapshot taken from space by a satellite designed to do something else.

Today, scientists are using InSAR, the "magic deformation camera" to study deformation at Yellowstone and elsewhere around the globe. Using the technique it has been possible to get an overall picture of Yellowstone deformation, revealing some interesting patterns of ground motion. We'll discuss some of these patterns in future issues of Yellowstone Caldera Chronicles.

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