Eye in the Sky

Zeroing in: satellite images, from continent to forest

Almost as soon as he arrived in Rio de Janeiro last July, Clinton Jenkins was robbed. He was riding a city bus when a man swiped his laptop computer and made for the door. Had the thief cared to inspect the contents of his new computer, he might have been surprised, and a bit concerned, by what he found: satellite images of Rio and the Atlantic Forest that surrounds it. Had he robbed a spy?, he might have wondered.

Jenkins is not a spy. He is a postdoctoral researcher who works with conservation ecologist Stuart Pimm, specializing in remote-sensing technology. He'd been teaching a course on remote sensing and geographical information systems (GIS) to conservation professionals at the Brazilian Institute for Ecological Research in nearby São Paulo that summer. The rest of the year, he assists his colleagues in the Nicholas School of the Environment and Earth Sciences at Duke.

As a concept, remote sensing is simple: It's the observation of any object from a distance. But when the object is the Earth and the distance is space, the observing gets a bit tricky. "You have to make the image interpretable," says Jenkins, "you have to get the colors right." The colors are the wavelengths of electromagnetic radiation reflected by objects on the ground (plants, trees, rivers, roads). Those wavelengths are recorded by the satellite as digital numbers, which are then transmitted to Earth, where scientists like Jenkins enter the data in a computer program to produce an image.

The satellites have the capacity, Jenkins explains, to distinguish between ranch and farm, grass and forest. Even among trees, the wavelengths vary. Levels of chlorophyll, the chemical in leaves that absorbs visible light, are higher in some trees than in others. But the satellite's most powerful feature, he says, is that it captures infrared light as well. "Infrared light isn't absorbed by the forest. So you get this very distinct signature of vegetation."

That's critical if, like Nicholas School graduate student Mariana Vale, you want to map a specific bird's habitat. Before leaving for the field, Vale knew from existing literature that the Rio Branco Antbird lived in gallery forest along a tributary of the Amazon. And the images she had analyzed indicated the presence of that vegetation. Once there, she recorded the Global Positioning System (GPS) points where she spotted the rare species. Back at the Nicholas School weeks later, she entered the data into a GIS program, which all Nicholas School computers are equipped with. Through the GIS, she could superimpose the bird's distribution onto a map of hydroelectric projects in the area and look for intersections between the two. The picture, she says, is not a pretty one.

Broadly speaking, satellite imagery is a picture that conservation cannot do without. Since they were first made available to the public in the early 1970s--when NASA launched the first of its low-orbit Landsat satellites--digital images of the Earth's surface have been more than a scientific resource. They've created global awareness of environmental crises and driven action at the national level. A landmark study in the journal Science in 1993 measured deforestation of the Amazon through a collection of more than 200 images taken between 1978 and 1988. "That really got people's attention," says Jenkins. "It was the first time anyone said, 'Look, this is what is happening on a massive, continental scale. It's not a myth.'"

Indeed, in addition to their scientific applications--soil surveys, mineral exploration, mapmaking, and many others--satellite images put the planet, in a sense, on public display. Anyone with access to the technology could keep an eye on the situation, monitor the progress of development projects, and report illegal activity.

Over the past year, Jenkins has been keeping tabs on the movements of two oil companies in the Ecuadorian Amazon. "You can see how close the road comes to the indigenous reserve," he says of one. "They've already broken their promise as to how close they would get." If he sees that road go further, Jenkins says, he'll notify the press. "The fact is, they may break laws, but whatever they do, the world's watching."