An assistant professor at Colorado State University, Michael Lefsky, has combined data from three NASA satellites to produce a global map of the height of the world's forests.
Knowing how tall the forests are will help scientists figure out how much carbon the trees can capture and store and how fast they're releasing it back into the Earth's atmosphere. That data should in turn help guide policies on climate change. Lefsky will publish a paper on his work next month in Geophysical Research Letters.
The three satellites are ICESat, Terra and Aqua. Lefsky appears to have caught ICESat before the satellite's last laser failed in February and it was taken out of commission.
On July 14, NASA flight controllers finished firing ICESat's thrusters to lower its orbit so gravity can drag it back to Earth. About 90 percent of the satellite is expected to burn up in the atmosphere -- NASA claims there's little harm from the rest, although the U.S. Space Surveillance Network is supposed to be watching for debris. A second generation ICESat won't be launched before 2015.(More later on what NASA plans to do in the meantime).
ICESat was using a laser technology similar to radar, called lidar, to measure global topography, vegetation, the mass of ice sheets and the height of aersols and clouds. From NASA:
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.
The data Lefsky used for his map comes from more than 250 million laser pulses from ICESat, collected over seven years. He says his alternative was counting and measuring tree trunks He filled in gaps in his data (since lidar pulses are so tiny) with data from an instrument on Terra and Aqua called MODIS which measures large-scale changes on Earth, like cloud cover and radiation, but not height.
So who has the tallest trees? From NASA:
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.
One puzzle Lefsky hopes to solve, according to NASA, is what happens to 2 billion tons per year of missing carbon dioxide, considering that humans generate 7 billion tons and the oceans and atmosphere only absorb five billion tons.
A senior scientist at the Jet Propulsion Lab, meanwhile -- Sassan Saatchi -- is relying on Lefsky's data to create forest biomass maps.
In a separate mapping project reported by the San Jose Mercury News (the tie-ins are carbon and lidar), researchers will be flying up and down the West Coast shooting light pulses to create the most detailed map of the coast yet.
That work is overseen by NOAA and is supposed to help determine how fast the Pacific Ocean is rising. It rose eight inches in the last century and could rise another 55 inches in this one if carbon dioxide-induced global warming isn't slowed