“Resource managers need to see forests down to the disturbance resolution—the scale at which parking lots or developments or farms are carved out by deforestation,” says Josef Kellndorfer of the Woods Hole Research Center (WHRC). His research team recently took it down to that level when they released the National Biomass and Carbon Dataset (NBCD) for the United States in April 2011.

“We are providing information on a management scale,” Kellndorfer notes. Forests in the U.S., as well as their carbon content, are mapped down to 30 meters, or roughly 10 computer display pixels for every hectare of land (4 pixels per acre). “This data set is a comprehensive view of forest structure and carbon storage, and it provides an important baseline for assessing changes in the future.”

Over six years, Kellndorfer, Wayne Walker, and their Woods Hole team collaborated with the U.S. Forest Service and the U.S. Geological Survey (USGS) to assemble a national forest map from space-based radar and optical sensors, computer modeling, and a massive amount of ground-based data. They divided the country into 66 mapping zones and ended up mapping 265 million segments of the American land surface. Kellndorfer estimates that the mapping database includes measurements of about five million trees.

The researchers started with data from the Shuttle Radar Topography Mission, which was flown on the space shuttle Endeavour in 2000. With that space radar, the USGS and NASA’s Jet Propulsion Laboratory constructed topographic maps of nearly all of Earth’s land masses from 60 degrees north latitude to 60 degrees south.

By 2005, Kellndorfer deciphered signals (the scattering surfaces) in the electromagnetic waves detected by the radar—data that revealed the height of the vegetation. Subtracting the height of the treetops from the elevation of the land, the scientists could estimate the height and density of the woody plants, trees, and shrubs covering the surface.

But those numbers were only the beginning. Kellndorfer’s team combined their data with the National Land Cover Database, which was built from Landsat satellite images of Earth’s surface. They examined the biology and geology of their picture. How do different land elevations affect the height and thickness of trees? What can and cannot grow at certain elevations?

The last piece of the puzzle was ground truth. Kellndorfer enlisted the aid of Elizabeth LaPoint and colleagues in the Forest Inventory and Analysis program of the U.S. Forest Service.

The federal foresters keep a census of the nation’s trees, maintaining a survey plot for every 6,000 acres of woodland, and measuring the trees within that plot at least once every five years.

Those plots, however, are not available for direct survey or study by Kellndorfer or anyone outside the service—a safeguard to protect the integrity of the data set and the rights of private property owners. So the Woods Hole team prepared thousands of data sets with 15 to 20 variables that LaPoint could compare to the forest inventory.

Lidar, radar, visible-light imagery, ground surveys, and computer models all bring slightly different answers to the same problem. Three different teams produced three different forest and carbon maps in a fifteen-month span. Groups at Stanford, the European Space Agency, Brazil, the U.S. Forest Service, and dozens of other institutions are pursuing similar questions, sometimes as competitors, sometimes as collaborators.

From a distance, the research can sometimes appear redundant. But parallel approaches and competition have always been the recipe for innovation and deeper understanding.

“We have a pretty good handle on forest area worldwide, but not as great a sense of the structure or the changes,” says Steve Running, a member of the Intergovernmental Panel on Climate Change. “We need a better global, annual measure of our carbon stocks. We need to know how things change each year through fire, new growth and re-growth, desertification, and deforestation.”

“How do we cover the whole world,” Running adds, “and do it every two to three years, which is what the science needs?”

The number of options for space-based mapping has gotten smaller. The ICESat mission ended in 2009. Its follow-on, ICESat II, is slated for launch in 2016, but will not necessarily be able to view forests in the same way as its predecessor. The synthetic aperture radar used for the Shuttle Radar Topography Mission provided a global picture of Earth’s landscape structure in early 2000; but the space shuttle was retired in July 2011. A similar technology could provide forest structure and cover globally every year if launched on the space station or another satellite.

Many forest researchers and ecologists were counting on a mission that was proposed years ago and recommended by the National Research Council in 2007—the Deformation, Ecosystem, Structure, and Dynamics of Ice satellite. DESDynl would combine radar and lidar technologies to get a three-dimensional view of forests and their carbon stock. But that mission was put on indefinite hold in the spring of 2011 as the U.S. government made deep budget cuts. Researchers are now looking for other means to fly those instruments in space.

“It’s similar to cancer research, where you have different laboratories and different countries pursuing the same problem,” said Jon Ranson. “Everyone is looking with a slightly different angle and methodology. Groups are collaborating as much as they can, and taking the data that are available and making the best of it. In the end, it’s complementary and it improves the overall science.”

The ultimate prize is a uniform, standardized map of forest heights and carbon stocks on all continents at one time. And that map should be updated and revised as human activities renovate our planet.

“We have a pretty good handle on forest area worldwide, but not as great a sense of the structure or the changes,” says Steve Running, a member of the Intergovernmental Panel on Climate Change. “We need a better global, annual measure of our carbon stocks. We need to know how things change each year through fire, new growth and re-growth, desertification, and deforestation.”

“How do we cover the whole world,” Running adds, “and do it every two to three years, which is what the science needs?”

The number of options for space-based mapping has gotten smaller. The ICESat mission ended in 2009. Its follow-on, ICESat II, is slated for launch in 2016, but will not necessarily be able to view forests in the same way as its predecessor. The synthetic aperture radar used for the Shuttle Radar Topography Mission provided a global picture of Earth’s landscape structure in early 2000; but the space shuttle was retired in July 2011. A similar technology could provide forest structure and cover globally every year if launched on the space station or another satellite.

Many forest researchers and ecologists were counting on a mission that was proposed years ago and recommended by the National Research Council in 2007—the Deformation, Ecosystem, Structure, and Dynamics of Ice satellite. DESDynl would combine radar and lidar technologies to get a three-dimensional view of forests and their carbon stock. But that mission was put on indefinite hold in the spring of 2011 as the U.S. government made deep budget cuts. Researchers are now looking for other means to fly those instruments in space.

Beyond Eco-3D, the Goddard team has been working with partners in Canada and Brazil to improve airborne forest mapping, which may be the best method the world will have until a space-based lidar and radar can be flown again.

What is it All Worth?

“It’s amazing how many people really need our data,” Saatchi notes. “I’ve been getting bombarded by emails from people who want these maps.”

Kellndorfer’s inbox is full, too. Hundreds of ecologists, forest managers, academic scientists, city planners, land conservation groups, timber companies, climate modelers, civil engineers, biologists, and fish and game managers have sought maps on an almost daily basis. More are likely to come as international negotiators move closer to treaties and economic markets for managing carbon emissions and storage.

“The work we’re doing can help put an economic value on forests,” says Goddard’s Doug Morton. “Policymakers and economists want to know forest carbon stocks at very fine spatial scales, and countries naturally need to improve their assessment of stocks to participate in a forest carbon market. This is a high-stakes game in the policy realm.”

Developing countries are taking stock of the carbon in their forests as part of an effort in climate change mitigation called Reducing Emissions from Deforestation and Degradation, or REDD+. Scientific partners from the United States and Europe are often called on for technological assistance.

“Carbon trading markets are going to be partly based on selling credits for forests,” says Running. “If there is going to be billions of dollars in carbon trading, then knowing where the carbon is and how much of it there is takes on huge political and economic importance. We need a coordinated, global monitoring plan in order to make it legitimate.”

1. Resources

2. Jet Propulsion Laboratory (2011) Terrestrial Carbon Cycle Research. Accessed September 15, 2011.

3. Woods Hole Research Center (2011) National Biomass and Carbon Dataset. Accessed September 15, 2011.

4. Related Reading

5. NASA Earth Observatory (2011) Notes from the Field: Eco3D—Exploring the Third Dimension of Forest Carbon. Accessed September 15, 2011.

6. NASA Earth Observatory (2011, June 16) The Carbon Cycle. Accessed September 15, 2011.

7. NASA Scientific Visualization Studio (2011, April 8) Intro to Lidar 3D. Accessed January 4, 2012.

8. NASA Earth Observatory (2010, July 22) Forest Canopy Heights Across the United States.Accessed September 15, 2011.

9. NASA Earth Observatory (2008, February 2) Tree Canopy Height from 1650 to 1992.Accessed September 15, 2011.

10. NASA Earth Observatory (2008, February 1) Ancient Forest to Modern City. Accessed September 15, 2011.