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NASA Gears Up for Forest Study

Photonics.com
Oct 2018
GREENBELT, Md., Oct. 25, 2018 — NASA’s Global Ecosystem Dynamics Investigation (GEDI) is set for its November launch, using high-resolution laser ranging to study Earth’s forests and topography from the International Space Station (ISS).

The scientific mission seeks to answer questions about how much deforestation has contributed to atmospheric carbon dioxide concentrations and how much carbon forests would absorb in the future. It is led by a research group at the University of Maryland, which is working in collaboration with a team at NASA that is designing the laser for GEDI.

“We wanted to design a laser that could enable lidar-based remote sensing for Earth science and planetary exploration missions,” said Paul Stysley, a laser engineer at NASA’s Goddard Space Flight Center.

The team designed a laser system that “is comparatively simple, has appropriate margin on performance specifications, and is well understood,” he added. “This, in turn, allows it to be efficient and adaptable to different missions, as well as robust in a space flight environment.”

Using lidar technology, researchers shoot laser energy pulses at Earth’s surface and precisely record their return timing. This data produces a 3D image in the form of vertical observation or a full-waveform that shows the world’s forest canopy and the topography of the ground beneath it. This technique is possible because the transmitted laser light pulses are reflected by the ground, trees, vegetation, or clouds, and then collected by GEDI’s receiver. The returning photons are directed toward detectors, which convert the brightness of the light to an electronic voltage that’s recorded as a function of time in 1-ns intervals. Time can be converted to range by multiplying it by the speed of light, with the full waveform being calculated by the recorded voltage as a function of range.

The laser system allows full-waveform data to be collected, which will provide the ground elevation and vegetation canopy height measurements on a global level. “The canopy and 3-D waveform data products are based on ones that have already been provided by NASA’s Land, Vegetation, and Ice Sensor facility on airborne lidar missions,” Stysley said. “The GEDI lasers were internally designed, fabricated, assembled, and tested by the Laser and Elecro-Optics branch at NASA Goddard … Our design is easily adaptable for follow-on vegetation lidar missions or for planetary missions that need an efficient laser altimeter.”

The GEDI mission will operate on the ISS for up to two years.

GLOSSARY
lidar
An acronym of light detection and ranging, describing systems that use a light beam in place of conventional microwave beams for atmospheric monitoring, tracking and detection functions. Ladar, an acronym of laser detection and ranging, uses laser light for detection of speed, altitude, direction and range; it is often called laser radar.
BusinessNASAGlobal Ecosystem Dynamics InvestigationGEDIlasersInternational Space Stationimagingdeforestationcarbon emissionsclimate changePaul StysleylidarAmericas

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