NASA is developing a laser-based instrument for deployment on the International Space Station that will probe the depths of Earth's forests from space in a bid to reveal more about their role in the planet's carbon cycle. After its completion in 2018, this Global Ecosystem Dynamics Investigation (GEDI) lidar will join the likes of the Soil Moisture Active Passive satellite in studying Earth's vegetation on a global scale.
"GEDI will be a tremendous new resource for studying Earth's vegetation," said Piers Sellers, deputy director of the Sciences and Exploration Directorate at NASA's Goddard Space Flight Center. "In particular, the GEDI data will provide us with global-scale insights into how much carbon is being stored in the forest biomass. This information will be particularly powerful when combined with the historical record of changes captured by the U.S.’s long-standing program of Earth-orbiting satellites, such as Landsat and MODIS."
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GEDI carries three specialized lasers and an optics system that divides the three beams into 14 tracks on the ground. These tracks will be spaced 1,640 (500 meters) apart, covering a total of around four miles (6.5 kilometers). And the system will systematically canvas all land between 50 degrees latitude north and south – enough to cover most of the tropical and temperate forests.
The lasers will send brief pulses of light – around 16 billion of them in a year – that are optimized to pass through the canopy of even very dense forests without causing harm to animals or vegetation, with the time taken for a return (i.e., reflected) pulse measured precisely and converted into a distance.
A return pulse develops its own unique fingerprint as it interacts with different materials (in this case, leafy tree tops versus branches and thick trunks), and this fingerprint provides enough extra information to allow calculations of the height of the trees and their canopies with an accuracy of around 3.3 feet (1 meter). And that, in turn, enables scientists to estimate how much biomass the trees contain and how much carbon they are storing.This is data that's missing from the current picture of how trees fit into the carbon cycle.
"One of the most poorly quantified components of the carbon cycle is the net balance between forest disturbance and regrowth," said Ralph Dubayah, the GEDI principal investigator at the University of Maryland. "GEDI will help scientists fill in this missing piece by revealing the vertical structure of the forest, which is information we really can’t get with sufficient accuracy any other way."
It's not just useful for studying the carbon cycle, either. GEDI's 3D maps could be combined with maps from other satellites to examine the role forest architecture plays in biodiversity and land use, or to monitor changes over time.
The GEDI lidar will be built at NASA's Goddard Space Flight Center, with the University of Maryland, College Park leading the project.