To Take Earth’s Pulse, You Have to Fly High

Satellite and airborne sensors won't cure the Earth. But they promise the clearest picture yet of its various ailments.

The view out the window was bad enough. As his research plane flew over groves of California’s giant sequoias, some of the world’s tallest trees, Greg Asner could see the toll the state’s four-year drought had taken. “It looked wicked dry down there,” he said. But when he turned from the window to the video display in his flying lab, the view was even more alarming. In places, the forest was bright red. “It was showing shocking levels of stress,” he said.

The digital images were coming from a new 3-D scanning system that Asner, an ecologist with the Carnegie Institution for Science, had just installed in his turboprop aircraft. The scanner’s twin lasers pinged the trees, picking out individual branches from 7,000 feet up. Its twin imaging spectrometers, one built by NASA’s Jet Propulsion Laboratory (JPL), recorded hundreds of wavelengths of reflected sunlight, from the visible to the infrared, revealing detailed chemical signatures that identified each tree by species and even showed how much water it had absorbed—a key indicator of health. “It was like getting a blood test of the whole forest,” Asner said. The way he had chosen the display colors that day, trees starved of water were bright red.

Disturbing as the images were, they represented a powerful new way of looking at the planet. “The system produces maps that tell us more about an ecosystem in a single airborne overpass,” Asner wrote later, “than what might be achieved in a lifetime of work on the ground.” And his Carnegie Airborne Observatory is just the leading edge of a broader trend.

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