The Cold War may be over, but satellites can now track new kinds of movement–some that might even threaten life as we know it.
For 20 years, radar images have monitored things like earthquakes, volcano eruptions and landslides. These might be big catastrophes from the human point of view, but from a global perspective, they are relatively minor occurrences.
What we haven't been able to do is track major events such as major earthquake ruptures and fast-moving sections of glaciers. What we need to do, is just that. We need to see how, with global warming glaciers are moving.
An electrical engineering graduate student at Caltech, Sebastien Leprince, has developed a software that can correlate changes in optical images to track large-scale changes. There was already a technique called InSAR in place. InSAR uses radar images to indicated ground displacement.
Yet according to Leprince, "InSAR is physically limited. It's good for small displacements, but not for large ones. The radar resolution isn't enough to look at deformation with a large gradient."
Leprince wasn't able to develop his new technique overnight. He began in 2003 when images correlation was "more like an art." Under the supervision of Jean-Philippe Avouac, geology professor and director of Caltech's Tectonics Observatory, he quickly identified four major steps, but wasn't sure what order to take them in.
One of the major steps was correcting the distortion caused by taking photos from space and then projecting them onto a surface. So the first step coordinates the image with coordinates on the ground. Then where the satellite was when the picture was taken needs to be taken into account. Just as when you take a photo of people on earth, there's bound to be a little distortion depending upon the angle of the camera. This has to be accounted for as does the topography. Lastly, images need to be combined and surface displacements measured.
Using this technique, Leprince was able to analyze several earthquakes including the 2005 Kashmir, Pakistan; 2002 Denali, Alaska; 1999 Hector Mine and Chi Chi, Taiwan; and 1992 Landers, California.
After Leprince released his software on the Tectonics Observatory website, he was contacted by a Canadian geologist, asking how to apply this toward the study of glaciers. Radar hasn't been effective in the analysis of glacier movement because the movement is too fast and the melting of the ice also poses a problem. Leprince commented, "The tectonic application was pretty well set up and we'd tested it thoroughly. So we extended it to glaciology." And then to other studies as well.
With movies like An Inconvenient Truth and animal conservationist warnings about species extinction due to shrinking Polar ice, such studies may be crucial to the future of this planet.
Leprince presented his research at the annual meeting of American Geophysical Union in San Francisco on Dec. 14. The January 1 issue of Eos, AGU's weekly newspaper will feature his research.