deforestation in the Loreto region of Peru in 2013 as seen from NASA's Landsat satellite.
Tropical forests are threatened by many types of farming, ranching, and human activity. One of the best ways to track those threats is through the Landsat series of satellites, developed by NASA and operated by the Geological Survey. The accessible and free archive of Landsat data makes it possible for scientists to monitor changes in remote landscapes without leaving their offices and labs. Remote sensing scientist Clinton Jenkins of North Carolina State University had just such an opportunity earlier this year. In July 2013, he received a tip from colleagues in South America about some possible deforestation in the Loreto region of Peru. Jenkins and colleagues then began combing through recently acquired Landsat images for signs of change. Within hours, they found an image with what appeared to be bare ground in previously intact forest east of Tamshiyacu, Peru. But the image was cloudy, a problem for remote sensing of most tropical regions in daylight. So the researchers waited. Every eight days, either Landsat 7 or Landsat 8 passed over the region, and every eight days, they got another cloudy image with hints but no confirmation of cleared forest. Finally on August 28, 2013, Landsat 8 got a clear view of the area. The image, from the Enhanced Thematic Mapper Plus on Landsat 7, shows the area on October 5, 2012. “Landsat imagery is essential for environmental monitoring because it is free, easy to access, and quickly available after the satellite passes over an area,” said Jenkins, who has been studying deforestation since he was a graduate student. “Satellites are the only way to monitor these areas because they are so large and so difficult to access.” By piecing together evidence from multiple Landsat 7 and 8 images, Jenkins and colleagues have estimated a deforestation rate of roughly 100 hectares (247 acres) per week in the tract
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