DESCRIPTION:
InSAR - Interferometric Synthetic Aperature Radar
Satellite Radar Interferometry

About 10 years ago, a remarkable new technique for measuring ground deformation from Earth orbit burst on the scene with all the drama of a major earthquake. Using a series of radar images acquired by the European Space Agency's ERS satellites, Didier Massonnet and others (1993) produced a striking image of ground displacements caused by the magnitude 7.3 Landers earthquake, which struck about 150 kilometers east of Los Angeles on 28 June 1992.

Geodesists around the world were struck by the remarkable detail visible in the image, which resembled the displacement pattern predicted by theoretical models of such an earthquake. The pattern had never before been fully observed in the field, because conventional ways of measuring ground deformation were capable of filling in only a few pieces of the puzzle. Suddenly, all of the pieces fell into place and the race was on to apply the amazing new technique, called satellite radar interferometry, to other sources of ground deformation, including volcanoes.

InSAR stands for Interferometric Synthetic Aperture Radar. This is thus a remote sensing technique that uses radar satellite images. Those radar satellite (ERS1, ERS2, JERS, IRS or Radarsat) shoot constantly beams of radar waves towards the earth and record them after they bounced back off the Earth's surface. ...

Volcanoes deform constantly. Obviously during eruptions, the magma injected from down below has to work its way through surrounding rock, and this creates slow ground movements that can be detected with InSAR. But also when a volcano is in relative quiescence, we can monitor the injection of magma at depth because that deformation too reaches the surface. Again, this tool allows us to understand better how volcano work.

Link to: USGS Earthquake Hazards Website for MORE "What Is InSAR" Information

[JPG,65K,InlineJPG]
InSAR Image, Three Sisters West Uplift
-- From: Wicks, May 2001

USGS scientists have detected a slight swelling, or uplift, of the ground surface over a broad area centered 5 kilometers (3 miles) west of South Sister volcano in the Three Sisters region of the central Oregon Cascade Range. The Three Sisters region is located 35 kilometers (22 miles) west of Bend, Oregon, and 100 kilometers (60 miles) east of Eugene, Oregon. The uplift, which occurred between 1996 and 2000, covers an area about 15 to 20 kilometers (9 to 12 miles) in diameter and the maximum amount of uplift at its center is about 10 centimeters (4 inches). It is too broad and low to be noticed from the ground, and several close aerial inspections of the area have revealed no unusual surface features.

The relatively new technique employed by the scientists, Satellite Radar Interferometry (or InSAR), uses satellite data to make radar images of a portion of the Earth.s surface. Images acquired at different times, but from the same location in space, can be used to detect even minor (a few centimeters or one inch) changes in the elevation of the ground. The images that reveal the 10-centimeter uplift near South Sister were obtained in 1996 and 2000. The exact timing of the uplift, or whether it is continuing at present, is unknown, but is being studied further.

Three Sister Information Statement, May 8, 2001

Three Sister West Uplift Menu

Satellite interferometric synthetic aperture radar is uniquely suited to monitoring year-to-year deformation of the entire Yellowstone caldera (about 3000 square kilometers). Sequential interferograms indicate that subsidence within the caldera migrated from one resurgent dome to the other between August 1992 and August 1995. Between August 1995 and September 1996 the caldera region near the northeast dome began to inflate, and accompanying surface uplift migrated to the southwest dome between September 1996 and June 1997. These deformation data are consistent with hydrothermal or magmatic fluid migration into and out of two sill-like bodies that are about 8 km directly beneath the caldera. ...

The main advantage of satellite interferometric synthetic aperture radar (InSAR) is its ability, under favorable conditions, to measure deformation of the entire caldera floor and its surroundings. By measuring a surface of deformation rather than movement at isolated points, we are able to locate and characterize deformation sources better than has been possible to date.

Link to: Wicks, et.al., courtesy USGS Earthquake Hazards Website

CVO Yellowstone Caldera Monitoring Menu

Return to:
[Volcano Monitoring - InSAR Menu] ...