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Radar views of Earth's movements to star at AGU meeting

Within the past few years, earth scientists in several fields have expressed their excitement about a new satellite-based radar technology called synthetic aperture radar (SAR) that can detect subtle changes on the Earth's crust ­ a volcano breathing, a glacier bending as it floats onto the sea, a faultline relaxing after a quake.

Nearly a dozen sessions at the Dec. 8-12 meeting of the American Geophysical Union contain reports of the use of SAR. "Scientists are continuing to expand the applications for spaceborne measurements of deformation on the Earth's surface," said Howard Zebker, Stanford associate professor of geophysics and electrical engineering and one of the developers of the SAR technology.

The technology uses radar pictures taken from satellites 500 miles or more up in space to track tiny movements on the surface of Earth over a large area and over weeks, months or years. It is often used in conjunction with ground-based Global Positioning System (GPS) instruments.

At the meeting in San Francisco's Moscone Center, scientists report on the use of SAR interferometry and GPS:

  • To measure changes in active volcanoes (see sessions V31A&B, V32B and V42C).
  • To view deformation of Earth's crust along faultlines in real time (G41A and G42A).
  • To track the movements of glaciers and ice sheets (U11B, H21D, H22G and H31A).

A Monday morning session, G11A, presents research to improve the quality of SAR technology. And Jean-Bernard Minster of the Institute of Oceanography will discuss SAR and other technologies for measuring the Earth in high-resolution detail in his speech for the annual Bowie Lecture to be delivered Monday, Dec. 8.

Zebker said, "Interferometric SAR is beginning to be used to study subtle phenomena, such as the deformations of volcanoes before eruptions, and a whole host of land subsidence issues such as withdrawal of water, oil or other fluids from the Earth's crust. In addition to studying the large co-seismic motions that occur during earthquakes, SAR is being used to gather more subtle data about the relaxation in stress after an earthquake, and to look for gradual buildup of stress over years ­ movement that often is not detectable by seismograms.

"In addition," he said, "scientists continue to use interferometric SAR as a tool for mapping the flow of ice sheets and glaciers, over large remote areas of the Earth, principally for large-scale modeling of the Earth's climate and possible man-induced changes such as are being discussed at the global warming conference in Japan."

Among the papers being presented at AGU by Stanford scholars is Zebker's poster on the use of SAR to detect a 7-millimeter-per-year uplift in salt domes along the Dead Sea (session G11-A17, Monday morning Dec. 8). Postdoctoral fellow Falk Amelung reports on subtle changes detected in Mexico's Popocatepetl and three Japanese volcanoes, in session V42C-10 on Thursday afternoon, Dec. 11.

Graduate student Sigurjón Jónsson reports in session H21-D9 on the sudden collapse of glaciers in Iceland after a jökulhlaup ­ an event caused when hot geothermal cauldrons melt the ice beneath the glacier, and a flood of water and mud drains away. Afterward, ice flows into the depression and builds up again at a rate of 2 to 18 centimeters per day, Jónsson reports.

REPORTERS' NOTE: Zebker will be attending the AGU Meeting Dec. 8-11. He will present a poster at session G11A on Monday morning, Dec. 8. Reporters can leave messages for him via e-mail or in the pressroom at AGU. Enclosed with this release are an earlier article about Zebker and an article that he wrote about SAR interferometry for Pacific Discovery magazine.


By Janet Basu

For additional information, see Howard Zebker's home page at
See also Space-borne radar to "revolutionize" views of Earth's hazards

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