DURHAM, N.C. – Satellite images are an increasingly powerful tool for monitoring the health of the planet. Researchers use them to measure everything from deforestation in the Amazon to melting icecaps at the poles.

But a new paper by a trio of researchers at the Nicholas School of the Environment and Earth Sciences at 91 is raising alarm that the network of satellites scientists rely on for these images is falling into disarray.

“This vital network of satellites is unraveling,” says Scott Loarie, a PhD student in conservation ecology at the Nicholas School and lead author of the paper, which was published this week inTrends in Ecology and Evolution.

“Never before have we had such an urgent need for environmental science and such powerful tools to make use of satellite images,” Loarie says. “But this year we lost both Landsats, two of our most important satellites. There is no replacement.”

Loarie’s co-authors on the paper are Stuart Pimm, Doris Duke Professor of Conservation Ecology, and Lucas Joppa, a fellow PhD student at the school.

The recent demise of NASA’s Landsat satellites has been a particularly hard loss for environmental scientists, they write. The mission began during the height of the U.S. space program, had taken images of the globe continuously since 1972 and was a mainstay of environmental research. In March of this year, Landsat 7, the most recent Landsat, was compromised by a malfunction. Landsat 5 had far outlived its expected lifetime but finally stopped imaging due to battery failure on October 6th. Even if the mission continues, a replacement won’t launch for more than a decade.

Because Landsat was a mid-range satellite that covered the entire globe every 14 days, researchers could use its detailed images to measure changes taking place in remote environmental hotspots anywhere on Earth over a period of several years or longer. In a pair of landmark studies recently published in Science, scientists at the Carnegie Institution used the satellite’s images to quantify deforestation in the Brazilian and Peruvian Amazon.

“They could actually see illegal and selective logging through the forest and were able to measure 60 to 123 percent more damage to the forest than scientists previously thought,” Loarie says. “Landsat made that discovery possible.”

“This gap in our Landsat image archive will be remembered as the Dark Ages in our ability to monitor our environment,” Joppa says.

Different satellites are used to measure different environmental processes. NASA’s MODIS satellite, for instance, images the entire globe every day and is well supported.  But while Landsat had 30-meter pixels, MODIS’s pixels are 250-meters across. At this resolution, many processes, such as selective logging, cannot be detected.

Fortunately, the private companies have begun launching a growing fleet of high-resolution (1 to 4 meter pixel) satellites. “These companies have done a fantastic job making their image archives available to scientists,” says Loarie, “and Google is increasingly making these archives available to the public on Google Earth.” The problem is that these high-resolution images can only image small parts of the globe and paying customers decide which parts of the globe they image. Hiring one of these satellites can cost thousands of dollars, so customers are most often corporations, and the images they request reflect economic interests and are clustered around cities and borders.  

“Our research found that many of the places that are likely to be most effected by environmental changes such as tropical forests where biodiversity is highest, landscapes in and around protected areas, and places such as the Arctic, where global warming is changing the planet most quickly are seriously under represented in these image archives,” Loarie says.

Rather than pointing the finger of blame, however, Loarie and his co-authors say the goal of their new paper is to urge the scientific community to work together with the government and the private sector to coordinate policies that will ensure that monitoring the Earth’s environmental priorities continues.

“When people think of the U.S. space program, they tend to think of exploring the moon or Mars,” says Pimm. “We forget the huge gains space technology has made towards monitoring our home planet. It would be a tragedy if our country— a mere half century after the space program began — became blind to our planet’s rapidly changing environment.”

Contacts: Scott Loarie, (919) 613-8057, cel: (707) 217-8479 or scott.loarie@duke.edu, or Stuart Pimm, (919) 613-8141 or StuartPimm@aol.com

For help reaching Loarie or Pimm, contact Tim Lucas at (919) 613-8084 or tdlucas@duke.edu