Satellite Imaging Isn't Just a Spy in the Sky Anymore

(Feb. 7) -- December's big global warming conference in Copenhagen featured lots of chatter about the future and ways to avoid environmental Doomsday. One of the surprise speakers was Tom Sever, NASA's recently-retired staff archeologist.

His topic, "Climate Change Impacts on Civilization: Lessons From Space Archeology," certainly sounds contemporary. But he broke ranks by choosing to look back a thousand years -- to the mysterious collapse of the Mayan empire.

Sever is one of the pioneers of satellite imaging technology, also known as remote sensing. His Mayan research (and Copenhagen appearance) is indicative of how far the field has come from the Cold War days of high-tech snooping for missile silos. Satellite imaging now figures into everything from disease prevention to monitoring human rights abuses.

"The applications of remote sensing are only going to keep increasing," says Sarah Parcak, assistant professor of archaeology at the University of Alabama-Birmingham, who has used it to discover more than 130 historic sites buried in the Egyptian desert. "It's a wonderful tool to track short-term and long-term changes, and it's fairly cost-efficient."

For about 20 years, Sever has been examining high-altitude pictures of the rain forests that blanket Central America's Yucatan Peninsula. He's able to look back through time by mining the images for information about such variables as soil content and moisture levels, then running that data through computer models.

His conclusion? The Mayans serve as a cautionary tale. They were voracious tree cutters, denuding the landscape to the point where it adversely affected crop yields and rainfall patterns. Multiple factors, including overpopulation, played a role in their demise, Sever notes, but deforestation "was one of them and perhaps a significant component."

Ron Blom, principal scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., shared the stage with Sever in Copenhagen. He delved even deeper into the past, talking about how the Earth's climate stabilized about 11,000 years ago, an "enabling circumstance" that allowed agricultural, non-nomadic societies to take root. But what nature gives, nature can take away.

According to Blom, satellite imaging has shown that the ancient cities of Petra in Jordan and Angkor Wat in Cambodia fell victim to brutally fickle weather. "Drought was the final thing that ruined them," he says.

Blom and Sever both stumbled into satellite imaging in the early 1980s. Blom was among the NASA scientists who were stumped by the images taken by radar-equipped cameras that had been placed aboard the Challenger space shuttle during its test flights. The photographed terrain looked otherworldly. They eventually realized they were staring at pictures of the Sahara Desert that contained radar-enhanced details the human eye normally couldn't see, particularly a spider's web of dried river beds hidden under what had once been lush grassland.

Inspiration struck. Blom became part of a team that directed an archaeological dig near where several of those latent rivers intersected in southern Oman. They were betting that might be a suitable location of the fabled lost city of Ubar. They guessed right.

"It's not an Instamatic snapshot," Blom says, referring to all the image manipulating that must be done with most raw satellite photos. "The surface you see with your eye is not the surface the radar sees."

Sever had taken a job fresh out of graduate school in 1978 as a data processor at Stennis Space Center in Mississippi. He began playing around with NASA's stock of satellite photos in his off hours. He eventually convinced NASA and the National Science Foundation to undertake a small demonstration project in the wilds of Costa Rica.

Boots-on-the-ground exploration subsequently confirmed a secret that satellite images first revealed to him: "We are able to find the oldest footpath in the world," Sever says.

Archaeologists immediately grasped the significance of satellite imaging. Eyes in the sky can scour hundreds of square miles of land, pinpointing those spots most worthy of pick-and-shovel exploration. But other uses gradually materialized.

Satellite imaging has expanded the scope of human rights activists. Before-and-after aerial photos documented the destruction of villages by government-backed militias in Sudan, as well as the flow of people into refugee camps, which helped the Red Cross better plan its relief efforts. Amnesty International maintains an Eyes on Darfur bank of photos on the Internet with help from the American Association for the Advancement of Science.

Other organizations have scoured satellite images to monitor Israeli army activity in the Gaza strip, political prison camps in North Korea and evidence of mass graves in northern Afghanistan.

Sever currently teaches at the University of Alabama-Huntsville but continues to do contract work for NASA. He assisted the governments of Central America in setting up a regional satellite surveillance system called Servir in 2005. It's being employed to detect forest fires and coastal outbreaks of toxic red tide, plus do comparative analysis of air quality. The Servir program has proved so successful that 15 African countries launched a spinoff in 2008.

In September, Parcak branched out from archaeology by being named director of a new Laboratory for Global Health Observation at the University of Alabama-Birmingham. Remote sensing identified heavy mosquito breeding areas in Kenya, which then get sprayed to reduce the threat of malaria. UAB is trying to develop similar preventive measures for Lyme disease, studying whether changes in ambient temperature and deer proliferation might be reliable predictors of tick infestations.

Parcak says satellites could play a critical role in locating sources of clean water: "That's going to be such a huge issue in the next 50 years, especially in Central Africa and India."

The increased popularity of satellite imaging is owed in part to improvements in the quality and quantity of raw material. Governments have released stockpiles of formerly classified photos into the public domain. Add to that the proliferation of commercial satellites that will shoot panoramic photos on request, although a 15-square-mile image can cost as much as $1,000.

Over the years, grainy black-and-white film has given way to high-resolution, full-color digital pictures. You have a choice of radar, near-infrared, thermal-infrared and LIDAR (Light Dilution and Ranging) formats.

Historically, this has been a strictly land-based technology, something of a handicap on a planet where two-thirds of the surface is submerged. But in October, a Colorado company launched a satellite that reportedly can capture images through almost 50 feet of water.

"I read that and my jaw dropped," Parcak says.

What's that about a lost city of Atlantis?