NASA Map Sees Earth's Trees in a New Light

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
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Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@jpl.nasa.gov

News release: 2012-044 Feb. 17, 2012

NASA Map Sees Earth's Trees in A New Light

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2012-044&cid=release_2012-044

PASADENA, Calif. – A NASA-led science team has created an accurate, high-resolution map of the
height of Earth's forests. The map will help scientists better understand the role forests play in
climate change and how their heights influence wildlife habitats within them, while also helping them
quantify the carbon stored in Earth's vegetation.

Scientists from NASA's Jet Propulsion Laboratory, Pasadena, Calif.; the University of Maryland,
College Park; and Woods Hole Research Center, Falmouth, Mass., created the map using 2.5 million
carefully screened, globally distributed laser pulse measurements from space. The light detection and
ranging (lidar) data were collected in 2005 by the Geoscience Laser Altimeter System instrument on
NASA's Ice, Cloud and land Elevation Satellite (ICESat).

"Knowing the height of Earth's forests is critical to estimating their biomass, or the amount of carbon
they contain," said lead researcher Marc Simard of JPL. "Our map can be used to improve global
efforts to monitor carbon. In addition, forest height is an integral characteristic of Earth's habitats, yet
is poorly measured globally, so our results will also benefit studies of the varieties of life that are
found in particular parts of the forest or habitats."

The map, available at http://lidarradar.jpl.nasa.gov, depicts the highest points in the forest canopy.
Its spatial resolution is 0.6 miles (1 kilometer). The map was validated against data from a network of
nearly 70 ground sites around the world.

The researchers found that, in general, forest heights decrease at higher elevations and are highest at
low latitudes, decreasing in height the farther they are from the tropics. A major exception was found
at around 40 degrees south latitude in southern tropical forests in Australia and New Zealand, where
stands of eucalyptus, one of the world's tallest flowering plants, tower much higher than 130 feet (40
meters).

The researchers augmented the ICESat data with other types of data to compensate for the sparse
lidar data, the effects of topography and cloud cover. These included estimates of the percentage of
global tree cover from NASA's Moderate Resolution Imaging Spectroradiometer on NASA's Terra
satellite, elevation data from NASA's Shuttle Radar Topography Mission, and temperature and
precipitation maps from NASA's Tropical Rainfall Measuring Mission and the WorldClim database.
WorldClim is a set of freely available, high-resolution global climate data that can be used for
mapping and spatial modeling.

In general, estimates in the new map show forest heights were taller than in a previous ICESat-based
map, particularly in the tropics and in boreal forests, and were shorter in mountainous regions. The
accuracy of the new map varies across major ecological community types in the forests, and also
depends on how much the forests have been disturbed by human activities and by variability in the
forests' natural height.

"Our map contains one of the best descriptions of the height of Earth's forests currently available at
regional and global scales," Simard said. "This study demonstrates the tremendous potential that
spaceborne lidar holds for revealing new information about Earth's forests. However, to monitor the
long-term health of Earth's forests and other ecosystems, new Earth observing satellites will be
needed."

Results of the study were published recently in the Journal of Geophysical Research –
Biogeosciences.

JPL is managed for NASA by the California Institute of Technology in Pasadena.

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