Real-time satellite monitoring spots small-scale changes in forests

Nature : By providing notification of changes in tree coverage, the Real Time System for Detection of Deforestation (DETER) has helped Brazil reduce its deforestation rate by 80% since 2004. However, DETER uses images from NASA’s Terra satellite, whose spectroradiometer has relatively low resolution—each pixel covers a 250 m² area. Therefore, the image-analysis software can take weeks or even months to detect changes, which makes it hard to flag illegal logging until a significant amount of forest has been affected. Now, Matthew Hansen of the University of Maryland in College Park and colleagues have created a similar system that uses data from NASA’s two Landsat satellites. Those satellites map Earth’s entire surface every eight days, and each pixel covers just 30 m². Hansen’s image-processing software can notice changes as subtle as a road appearing in a previously undeveloped area. The researchers plan to update images on their website within hours of detecting changes, and beginning in March, the World Resources Institute will release deforestation alerts.