"What we really want is a map of above-ground biomass, and the height map helps get us there," said Richard Houghton, an expert in terrestrial ecosystem science and the deputy director of the Woods Hole Research Center.
Lefsky used data from a laser technology called LIDAR that's capable of capturing vertical slices of surface features. It does so by shooting pulses of light at the surface and observing how much longer it takes for light to bounce back from the ground surface than from the top of the canopy. Since LIDAR can penetrate the top layer of forest canopy, it provides a fully-textured snapshot of the vertical structure of a forestsomething that no other scientific instrument can offer.
Lefsky based his map on data from more than 250 million laser pulses collected during a seven-year period. Each pulse returns information about just a tiny portion of the Earth's surface, so the project completed direct LIDAR measurements of only 2.4 percent of the planet's forested surfaces. To complete the map, Lefsky combined the LIDAR data with information from the Moderate Resolution Imaging Spectroradiometer (MODIS), a satellite instrument aboard both the Terra and Aqua satellites that senses a much broader swath of Earth's surface, even though it doesn't provide the vertical profile.
The next generation LIDAR measurements of forests and biomass, which will improve the resolution of the map considerably, could come from NASA's Deformation, Ecosystem Structure and Dynamics of Ice (DESDynI) satellite, proposed for the latter part of this decade.
|Contact: Steve Cole|
NASA/Goddard Space Flight Center