By Sally Pobojewski
News and Information Services
Using space-age technology they developed, University of Michigan scientists will help NASA’s space shuttle Endeavour count trees in a 2,500-square-mile section of Michigan’s Upper Peninsula. The shuttle is scheduled for launch on Thursday (April 7).
“The immediate goal of the experiment is to use radar imaging data from space to count the number of trees in the forest and see how big they are,” says Craig Dobson, assistant research scientist at the College of Engineering’s Center for Space Terahertz Technology.
“The long-term objective is to learn more about Earth’s environment, specifically the impact trees and other plant life may have on global warming and climate change.”
Using remote sensing data transmitted from an instrument in the shuttle’s payload bay, U-M scientists will produce full-color images of the heavily forested test site, which will be displayed during NASA news conferences to take place at 2 p.m. CDT daily throughout the nine-day mission at Houston’s Johnson Space Center.
Growing plants soak up significant amounts of carbon dioxide from the atmosphere and play a major role in the global carbon cycle—the delicate balancing act that regulates the exchange of carbon between Earth’s atmosphere, oceans and plants, according to Dobson. Many scientists believe people are adding too much carbon dioxide to the atmosphere by cutting down forests and burning fossil fuels. These scientists say human activity is forcing the carbon cycle out of balance, leading to a warmer planet and major climate changes in the future.
“There’s tremendous disagreement on how global warming could change climate conditions on a regional and local level,” Dobson says. “Before scientists can make valid predictions, we need to know more about the global distribution of plant life and the amount of carbon stored in the world’s forests.”
During the NASA mission, SIR-C—a Shuttle Imaging Radar instrument designed by NASA—and X-SAR—a Synthetic Aperture Radar instrument designed by the German and Italian space agencies—will shoot rapid radar pulses at a target area on the ground and collect echoes from those pulses as they bounce back up to the shuttle. Scientists will interpret these radar pulse echoes using specialized technology developed at the U-M to produce detailed high-resolution, color-coded images of vegetation patterns in Michigan’s Upper Peninsula.
During the mission, SIR-C will observe hundreds of sites on Earth from several different viewing angles. Nineteen of these sites, including the one at Raco, Mich., are designated as “supersites,” or areas of critical interest to the mission. The Raco supersite lies directly beneath shuttle orbit crossover points. “At crossover points, the shuttle passes overhead twice in each 24-hour period, instead of just once,” Dobson explains. “It gives us an opportunity to collect twice as much data.” Other supersites in the United States are at Duke Forest, N.C.; Death Valley, Calif.; and Chickasha, Okla.
Radar imaging with SIR-C has significant advantages over current remote sensing satellites that use optical technology, according to Dobson. “With radar imaging, you can see through clouds and at night,” he says. “SIR-C’s longer radar wavelength passes through the tree tops to bounce off the lower branches and trunks. This lets us make accurate estimates of the total amount of biomass or plant material in the forest.”
To verify the accuracy of the SIR-C imaging data, Dobson will monitor its radar signals with calibration equipment on the ground. He also plans to compare radar-based biomass estimates with previous field measurements he and his students made of trees in 70 ten-acre plots scattered throughout the test site.
The entire experiment will be repeated this August during a second NASA space shuttle mission, Dobson says. “It will give us one set of forest data with snow cover and one set with leaf cover.” During the August follow-up mission, the U-M research team will also use SIR-C to measure soil moisture in areas of the test site not covered with dense forest.
If the radar imaging experiment over Raco works as well as Dobson hopes,
U-M scientists plan to use their imaging technology to interpret existing remote sensing data from sites all over the world.
Others involved in the Raco experiment from the U-M include Fawwaz T. Ulaby, the R. Jamison and Betty Williams Professor of Electrical Engineering and Computer Science; Kamal Sarabandi, assistant professor of electrical engineering and computer science; Leland E. Pierce, assistant research scientist in electrical engineering and computer science; and a team of 15 graduate students from the College of Engineering and the School of Natural Resources and Environment.
