ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Sunday, September 8, 1996 TAG: 9609100010
SECTION: HORIZON PAGE: 1 EDITION: METRO
SOURCE: WILLIAM J. BROAD THE NEW YORK TIMES
The surface of the Earth is alive with motions too subtle for direct human observation, the slow wrinkling of the planetary skin, that pose considerable risks to cities and people. Slow shifts of the Earth's plates regularly build up strains that cause earthquakes. Volcanoes swell before they explode. Glaciers move and polar ice packs break up as the earth warms, raising seas and threatening to flood coastal areas.
Since the birth of modern science, such motions have been known to exist but have been excruciatingly hard to monitor on a regular basis, which is the kind of surveillance needed for thorough study and hazard warning.
Now, however, a new kind of space radar is beginning to map the Earth in stunning topographic detail and to reveal a wide range of previously hidden creepings, swellings and subsidences. With at least four satellites in orbit and more planned, the results of this mapping are exciting scientists around the globe and energizing a number of fields, including geology, climatology, hydrology, ecology and hazard prediction.
``It's a great leap forward,'' said Dr. Howard A. Zebker, a geophysicist and electrical engineer at Stanford University who helped develop the technique. ``It's like suddenly having X-rays to see inside a body.'' He said it was now possible to see things happening on the Earth's surface that were previously hidden from scientific view.
The method goes by the tongue-twisting name of synthetic aperture radar interferometry.
To date, it has produced spectacular images of slight but significant changes in places like Landers, Calif., where a 1992 earthquake shattered the high desert east of Los Angeles; Kobe, Japan, where a 1995 earthquake killed thousands of people; Mount Etna, Sicily, where an eruption between 1991 and 1993 unexpectedly shrank the old volcano; the ice fields of Chile, where a glacier surged forward in 1994; and Antarctica, where a huge ice floe that may have have been produced by global warming was monitored in 1992 in great detail.
Snapped by satellites hundreds of miles up, the radar images of the planet's surface include bands that indicate elevation shifts on the ground as small as 3 centimeters, or a little more than an inch.
Late last month, Zebker and some 200 other experts met in Sioux Falls, S.D., to help plan a new generation of American radar satellites meant to advance the field beyond the craft now in orbit, which were built by Europe, Japan and Canada. One aim is to increase the precision of change measurement to less than a centimeter, or about a third of an inch.
Although the United States pioneered the technology of space radars in the late 1970s, it now has no civilian radar satellites, a void that American scientists are increasingly eager to fill.
The Sioux Falls meeting was sponsored by the U.S. Geological Survey, which wants to improve its earthquake predictions, and by NASA's Jet Propulsion Laboratory in Pasadena, Calif., which built the first space radars nearly two decades ago.
Dr. David T. Sandwell of the Scripps Institution of Oceanography in La Jolla, Calif., who discusses the radar method in the current issue of the journal Science, said it had major implications for monitoring not only natural changes but also those caused by human activity.
For instance, pumping underground oil and water to the surface can cause the ground to sink over wide areas. Monitoring the beginnings of such sinking could aid in planning land use and putting controls on pumping. And nuclear explosions deep underground make telltale depressions at the surface, the tracking of which could aid arms control.
``It's revolutionary,'' Sandwell said of the radar technique in an interview. ``There are all kinds of neat things you can do.''
UNDATED: can do.''
Since the start of the space age, most satellites that peer over great distances to observe regions on the ground, both for spying and environmental assessment, have done so with cameras similar in principle to those of any tourist. They work in or near the visual part of the electromagnetic spectrum.
In 1978, however, the National Aeronautics and Space Administration launched a satellite of an entirely new kind that made its images not with light but by bouncing radio waves off the ground. Known as Seasat, this craft publicly revealed how radar satellites could portray both land and sea in striking new ways.
A major advantage was that the satellite worked at night or in foul weather. The radio waves with their long wavelengths easily pierced the clouds, a feat impossible for visible light and its short wavelengths.
The name ``synthetic aperture radar'' came from the method used to overcome the setup's main weakness. By nature, the long radio wavelengths of a radar system produce very low resolution, not showing details anywhere near as small as those delineated with light.
So the satellite's movement in orbit was exploited by using computer processing to turn the craft into a vast antenna stretching over dozens of miles of space. Rather than treating the satellite as an ordinary camera that takes a single snapshot, the new technique, in effect, keeps the shutter open as the satellite moves over wide regions of space. The step greatly increases the number of incoming radar echoes gathered up for a particular image, artificially increasing the aperture and sharply enhancing the resolution to nearly that of light-operated cameras.
Dr. Richard M. Goldstein, a scientist at the Jet Propulsion Laboratory, had a hunch that Seasat's abilities were even greater. He knew that the time it took Seasat's radar waves to bounce off the ground gave precise readings of distance. Such readings of the same object on the ground could be repeated from slightly different places in orbit, on different satellite passes, producing beneficial interference patterns. Those patterns might give a kind of stereoscopic image, three-dimensional and quite revealing of the elevation of terrestrial features below.
``So I wrote some proposals,'' Goldstein recalled in an interview. ``Unfriendly referees said it wouldn't work. But we tried it on Seasat and, lo and behold, it worked beautifully.''
That was the birth of synthetic aperture radar interferometry in satellites, which produced unique views of terrestrial topography, revealing all kinds of terrain features in three dimensions. In retrospect, it is clear that the next great step in the topographic art was to compare such scenes over time - over months and years - so that slow and subtle changes in the motions of the earth's surface could be observed. .
But that step proved to be painfully hard to take. The radar feats of Seasat came to an abrupt end in 1978 when the spacecraft failed unexpectedly after 100 days of operation. And NASA, for reasons that are unclear, chose to abandon satellite radars despite the craft's many successes. Instead, it flew radar missions on the space shuttle in 1981, 1984 and 1994.
The shuttle missions gathered data for days, not months or years, and thus disclosed relatively little about gradual terrestrial change.
Although NASA gave up radar satellites, the Government did not. In 1988, inspired by Seasat, it launched the first of a new class of spy satellites that used radar to peer through clouds and darkness, advancing the art of orbital espionage.
Among other things, such spy satellites and their powers of radar interferometry were used to make global topographic maps that proved vital to the self-navigation of cruise missiles. Such smart weapons were stars in the 1991 war against Iraq after it invaded Kuwait.
The first vivid and public demonstrations of how space radars could reveal subtle physical changes on the planet's surface came from the European Space Agency's Earth Remote Sensing One satellite, which was launched in 1991. ERS-1 showed the subtle terrain repercussions of a huge ice floe in Antarctica in 1992 and an earthquake that in 1992 shook the high desert east of Los Angeles.
Radar satellites were launched by Japan in 1992, Canada in 1995 and Europe again in 1995. Among the most striking results of these foreign efforts was a detailed elevation-change map of the area around Kobe, Japan, which was generated by comparing space topographic images before and after the great earthquake of 1995. Over wide areas, the interferogram revealed inches of elevation change that were clearly linked to the main upheaval.
American researchers were able to study and process some of this foreign data. As the power and elegance of the interferometry technique was driven home, they began to clamor for their own dedicated radar satellite.
Freeman of Jet Propulsion said the United States was actually ahead of the international pack technologically, if not in data collection, since the repeated shuttle-radar missions over more than a decade had resulted in rapid advances in the synthetic-aperture art.
And Sandwell of Scripps said this technological strength could easily translate into operational strength as well. ``We could leapfrog them,'' he said of the foreign efforts.
In the current planning frenzy, at least two American proposals are making the rounds but have yet to receive approval. One is known as Lightsar, for Light Synthetic Aperture Radar, and the other is known as ECHO, for Earth Change and Hazard Observatory. Given the budgetary squeeze in Washington, both are envisioned as costing very little compared with foreign and previous American programs - on the order of $100 million each.
Recently approved is a new shuttle mission in 2000 in which NASA and the Pentagon's Defense Mapping Agency are joining to build a special radar with a 200-foot-long boom that will produce an advanced topographic map of earth.
The planned high-resolution map is considered an ideal baseline for the measurement by future shuttle missions and radar satellites of subtle shifts on the surface of the earth over the course of months, years and decades - shifts that in theory will open a striking new window on the workings of the planet.
``I'm really excited,'' said Dr. Miriam Baltuck, the scientific head of space radars at NASA headquarters in Washington. ``There's a lot happening. This is cutting edge.''
PLEASE SEE EARTH/6
By WILLIAM J. BROAD
THE NEW YORK TIMES
The surface of the Earth is alive with motions too subtle for direct human observation, the slow wrinkling of the planetary skin, that pose considerable risks to cities and people. Slow shifts of the Earth's plates regularly build up strains that cause earthquakes. Volcanoes swell before they explode. Glaciers move and polar ice packs break up as the earth warms, raising seas and threatening to flood coastal areas.
Since the birth of modern science, such motions have been known to exist but have been excruciatingly hard to monitor on a regular basis, which is the kind of surveillance needed for thorough study and hazard warning.
Now, however, a new kind of space radar is beginning to map the Earth in stunning topographic detail and to reveal a wide range of previously hidden creepings, swellings and subsidences. With at least four satellites in orbit and more planned, the results of this mapping are exciting scientists around the globe and energizing a number of fields, including geology, climatology, hydrology, ecology and hazard prediction.
``It's a great leap forward,'' said Dr. Howard A. Zebker, a geophysicist and electrical engineer at Stanford University who helped develop the technique. ``It's like suddenly having X-rays to see inside a body.'' He said it was now possible to see things happening on the Earth's surface that were previously hidden from scientific view.
The method goes by the tongue-twisting name of synthetic aperture radar interferometry.
To date, it has produced spectacular images of slight but significant changes in places like Landers, Calif., where a 1992 earthquake shattered the high desert east of Los Angeles; Kobe, Japan, where a 1995 earthquake killed thousands of people; Mount Etna, Sicily, where an eruption between 1991 and 1993 unexpectedly shrank the old volcano; the ice fields of Chile, where a glacier surged forward in 1994; and Antarctica, where a huge ice floe that may have have been produced by global warming was monitored in 1992 in great detail.
Snapped by satellites hundreds of miles up, the radar images of the planet's surface include bands that indicate elevation shifts on the ground as small as 3 centimeters, or a little more than an inch.
Late last month, Zebker and some 200 other experts met in Sioux Falls, S.D., to help plan a new generation of American radar satellites meant to advance the field beyond the craft now in orbit, which were built by Europe, Japan and Canada. One aim is to increase the precision of change measurement to less than a centimeter, or about a third of an inch.
Although the United States pioneered the technology of space radars in the late 1970s, it now has no civilian radar satellites, a void that American scientists are increasingly eager to fill.
The Sioux Falls meeting was sponsored by the U.S. Geological Survey, which wants to improve its earthquake predictions, and by NASA's Jet Propulsion Laboratory in Pasadena, Calif., which built the first space radars nearly two decades ago.
``The science community is saying, `Wow, there's all kinds of things we can do with this,''' Dr. Tony Freeman, head of radar science and engineering at the propulsion lab, said in an interview. ``It's a measurement tool. It makes very precise measurements of topographic change, and we're just beginning to investigate the implications of that.''
Dr. David T. Sandwell of the Scripps Institution of Oceanography in La Jolla, Calif., who discusses the radar method in the current issue of the journal Science, said it had major implications for monitoring not only natural changes but also those caused by human activity.
For instance, pumping underground oil and water to the surface can cause the ground to sink over wide areas. Monitoring the beginnings of such sinking could aid in planning land use and putting controls on pumping. And nuclear explosions deep underground make telltale depressions at the surface, the tracking of which could aid arms control.
LENGTH: Long : 238 lines ILLUSTRATION: PHOTO: Sicily's Mount Etna, shrank after it erupted in theby CNBearly 1990s. That was just one of the spectacular images of slight
but significant changes revealed by synthetic aperture radar
interferometry