SCIENCE / MEDICINE : Keeping Tabs on our Changing Earth : Environment: Equipment aboard aircraft and satellites are at the cutting edge of environmental science. One day the devices may enable scientists to predict life-threatening global changes before they can be detected from the ground.

It was turquoise in surrounding hills and water from a nearby stream that attracted prehistoric Anasazi Indians to a sun-scorched plateau south of what today is Santa Fe, N. M.

But how their community of 600 people survived a severe drought in the 1400s was a mystery until a jet equipped with infrared cameras scanned the ruins of Pueblo San Marcos and detected dozens of grassy fields--all of them covered with pebbles.

Now, an unlikely marriage of geographers, anthropologists and physicists at the University of Colorado’s Center for the Study of Earth from Space believe that these man-made “pebble-mulch fields” forestalled mass starvation--and could do the same today in other arid regions of the world.

The discovery is one of many turning up at the center, which was established in the mid-1980s to study environmental change with equipment aboard aircraft and satellites once reserved for spying and spotting mineral deposits.

Remote sensing, as it is called, is the cutting edge of environmental science and may one day enable scientists to predict life-threatening global changes before they can be detected from the ground, said Alexander Goetz, director of the center.

The center is one of a growing number around the world aiming a new generation of remote sensing devices at places where change is magnified, such as the interfaces of land and sea, forest and meadow, urban development and wetlands.

The devices typically bounce radar waves, for example, at an area and then record the echo, or they detect infrared waves reflected naturally by the land’s surface. The reflected waves contain information ranging from the environmental impact of prehistoric human activities to the composition of plants.

“In the past, we had to pull a plant out by its roots, grind it up and run a chemical analysis to know, for example, its nitrogen intake,” Goetz said. “Because of the development of new remote sensing instruments, we are now able to do almost the same kind of analysis without touching the plant.”

In the forefront of the effort to monitor global change from afar, NASA is preparing to launch a series of instrument-loaded platforms in 1997 that will make up the Earth Observing System. The system will collect information on plants, soil, air, water, snow and even lightning around the globe every two days.

The goal is to provide an early warning system for detecting conditions such as drought, global warming, pollution and ozone.

“We are talking about a project that will cost $17 billion over the next decade,” said Brian Dunbar, a spokesman for the National Aeronautics and Space Administration. “It will enable us to look at the Earth as a system of complex interactions rather than from the perspective of individual scientific disciplines.”

The first platform will carry a desk-sized, 1,000-pound high resolution imaging spectrometer, which is being developed under the guidance of Goetz and 13 other scientists from throughout the country.

This device will pinpoint images of land and water as small as 100 feet across and provide an unprecedented bounty of information on each that will keep researchers busy for decades.

Scientists from several fields, Goetz said, “will have the job of sipping from this new fire hose of data and making sense of it.”

As it stands, the use of remote sensing devices for other than defense or industry-related purposes is so new that the meaning of the results is not always immediately apparent.

The discovery of the Anasazi’s response to 10 years of severe drought is a case in point.

Infrared photographs taken from the NASA jet reveal 96 mysterious patches on hillsides within walking distance of Pueblo San Marcos. Because heat from living organisms appears dark on infrared film, the patches seemed to suggest meadows in a landscape of cactus and bunch-grass.

Ground crews dispatched to the site, however, determined they were 60-foot-by-60-foot plots covered with a layer of pebbles to retain moisture. The pebbles also raise the temperature of the soil, which may have extended the Indians’ growing season for squash, maize and beans.

“It was a brilliant adaptation to an arid environment,” said geographer Dale Lightfoot, who, along with anthropologist Frank Eddy, first spotted the pebble-mulch fields in 1988 while examining the infrared photographs.

This year, Lightfoot hopes to initiate a project to test the practical applicability of similar pebble-mulch farming techniques in drought-prone nations in Africa and Latin America.

“Pebble-mulch fields could fit like a glove in Third World countries that depend on subsistance farming,” Lightfoot said. “Modern agricultural techniques in these countries improve crop yields, but they also pollute the environment and eliminate traditional jobs.”

To be sure, not all of the findings discovered in the center are as optimistic as the Anasazi’s innovative farming techniques.

Another study, for example, is examining whether the greenhouse effect could revive dormant “megadunes” on Colorado’s eastern plains and turn the Denver area into a dust bowl within 20 to 30 years.

“Our models suggest that in the next few decades global temperatures will climb to levels of 5,000 years ago,” said Steve Forman, a professor of geology at the center. “If that happens, the dunes will start moving again.”

The theory is based on the presumption that a rise in average temperature will kill off the plants and grasses that have anchored the two-mile-long dunes for thousands of years.

“If I am right,” Forman said, “it frightens me that in my son’s lifetime this area could become a much more arid place.”

A similar revival of long-dormant dunes could be expected on the high plains of China, which is one of the poorest and most densely populated areas in the world, Forman said.

Separately, Brian Curtiss, a researcher at the center, is developing a device the size of a shoe box that can instantly determine the nitrogen and chlorophyll content of plants and trees simply by aiming it at them from a few feet away.

The instrument analyzes light reflected from the surface of a plant. It can detect a reduction of chlorophyll, which plants use to absorb sunlight and produce new tissue.

Curtiss, along with Susan Ustin, a research associate at UC Davis, used similar technology last year to demonstrate that smog has caused greater damage than previously believed to the forests of California’s Sequoia National Park.

“These techniques allowed us to detect the effects of pollution at an earlier stage,” Curtiss said, “which gives government an extra few years to institute new policies and pollution standards to save the trees.”

Jeff Richey, an oceanographer at the University of Washington, Seattle, has begun using remote sensing equipment to study biological changes in the Amazon Basin caused by deforestation.

“Picture me in a boat on a river in the Amazon. What can I see? Not very much,” Richey said. “Remote sensing is a tool with which I can see the whole forest, and what it’s made of.”

Still, Richey, like many other scientists turning to remote sensing, acknowledged that it is “a tool whose potential we are only beginning to recognize.”