Steve Cole
Headquarters, Washington
202-358-0918
stephen.e.cole@nasa.gov
Sarah DeWitt
Goddard Space Flight Center, Greenbelt, Md.
301-286-0535
sarah.l.dewitt@nasa.gov
RELEASE: 10-173
FIRST MAP OF GLOBAL FOREST HEIGHTS CREATED FROM NASA DATA
WASHINGTON -- Scientists have produced a first-of-its kind map of the
height of the world's forests by combining data from three NASA
satellites. The map will help scientists build an inventory of how
much carbon the world's forests store and how fast that carbon cycles
through ecosystems and back into the atmosphere.
Maps of local and regional forest canopy have been produced before,
but the new map is the first that spans the entire globe using one
uniform method. The map was based on data collected by NASA's Terra
and Aqua satellites, along with the Ice, Cloud and land Elevation
Satellite, or ICESat. Michael Lefsky, a remote-sensing specialist
from Colorado State University in Ft. Collins, produced the final
product. Lefsky describes his results in a journal paper to be
published next month in Geophysical Research Letters.
The new map shows the world's tallest forests are clustered in North
America's Pacific Northwest and portions of Southeast Asia. Shorter
forests are found in broad swaths across northern Canada and Eurasia.
The primary data Lefsky used was from a laser technology called lidar
on the ICESat. Lidar can capture vertical slices of forest canopy
height by shooting pulses of light at the ground and observing how
much longer it takes for light to bounce back from the surface than
from the top of the forest canopy. Since lidar can penetrate the top
layer of forest canopy, it provides a detailed snapshot of the
vertical structure of a forest.
"Lidar is unparalleled for this type of measurement," Lefsky said. "It
would have taken weeks or more to collect the same amount of data in
the field by counting and measuring tree trunks that lidar can
capture in seconds."
Lefsky based the map on data from more than 250 million laser pulses
collected during a seven-year period. Because each pulse returns
information about a tiny portion of the surface, lidar offered direct
measurements of only 2.4 percent of the Earth's forested surfaces. To
complete the map, Lefsky combined the lidar data with information
from the Moderate Resolution Imaging Spectroradiometer (MODIS), an
instrument aboard NASA's Terra and Aqua satellites. MODIS observes a
broad swath of Earth's surface, even though it does not supply the
vertical profile.
The new results show that temperate conifer forests -- which are
extremely moist and contain massive trees such as Douglas fir,
western hemlock, redwoods, and sequoias -- have the tallest canopies,
soaring above 131 feet. In contrast, boreal forests dominated by
spruce, fir, pine, and larch had canopies typically less than 66
feet. Relatively undisturbed areas in tropical rain forests were
about 82 feet tall, roughly the same height as the oak, beeches, and
birches of temperate broadleaf forests common in Europe and much of
the United States.
Measuring canopy height has implications for efforts to estimate the
amount of carbon tied up in Earth's forests and for explaining what
absorbs 2 billion tons of "missing" carbon each year. Humans release
about 7 billion tons of carbon annually, mostly in the form of carbon
dioxide. Of that, 3 billion tons end up in the atmosphere and 2
billion tons in the ocean. It's unclear where the remaining 2 billion
tons of carbon go, although scientists suspect forests capture and
store much of it as biomass through photosynthesis.
The new forest height map is a step toward a global map of all
above-ground biomass. Sassan Saatchi, senior scientist at NASA's Jet
Propulsion Laboratory in Pasadena, Calif., already has started
combining the height data with forest inventories to create biomass
maps for tropical forests. Global biomass inventories will eventually
be used to improve climate models and guide policymakers on carbon
management strategies.
The next generation lidar measurements of forests and biomass, which
will improve the detail of the map considerably, could come from a
planned NASA satellite mission, called the Deformation, Ecosystem
Structure and Dynamics of Ice project. It is slated to launch no
earlier than 2017.
For images and additional information about the map, visit:
http://www.nasa.gov/topics/earth/features/forest-height-map.html
For more information about NASA and agency programs, visit:
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