A three-year project to measure the productivity of four forests in different climate conditions, will simultaneously collect data from NASA’s MODIS satellite (above), from a plane equipped with a specially designed device, and from towers within the forests themselves (below). “We still do not know how much carbon different forests are taking in, and this is one of the last issues to be resolved in climate change discussion,” says Faiz Rahman. Credit: Images, courtesy NASA, Faiz Rahman lab

INDIANA U. (US) —Satellites are frequently used to study climate change, but how accurate is the data?

Climate scientists and ecologists use information gathered from satellites to determine how productive forests are and to understand how temperature and weather changes are influencing the use of carbon—the productivity or health—of natural resources.


“This is an integral part of global climate change,” says Faiz Rahman, an expert on the use of satellite data to study complex terrestrial ecosystems, at Indiana University.

“We still do not know how much carbon different forests are taking in, and this is one of the last issues to be resolved in climate change discussion.

“What will be the impact of changing climate on carbon absorption and carbon production? This issue connects directly to global change, and will make it easier for us to predict what will happen so we can make intelligent decisions.”

Satellites are frequently used to collect light data from Earth’s surface for analysis, but questions about the accuracy or usefulness of this data in recent years convinced Rahman and colleagues that a comparison of satellite and near-to-surface data is needed.

Of particular concern is the relative tradeoff between spatial and temporal resolutions of satellite data. The images of Earth produced by NASA’s MODIS satellite, for example, cover the whole Earth twice every day—but lack spatial details at the forest canopy level.

The project will gather data from four forests at three heights, simultaneously. During a 30-minute window, NASA’s MODIS satellite will fly over a target forest, providing images from low Earth orbit (about 420 miles above sea level).

During that same half-hour, project scientists will gather information about forest productivity from airplane fly-overs at 3,000 feet and from towers within the forest canopies. The chartered airplane will be specially fitted with equipment that simulates satellite imaging systems, but at much higher spatial resolution.

The scientists plan 600 data-gathering days over the next three years, about 150 days per forest. Study sites include Morgan-Monroe State Forest (Ind.), Duke Forest (N.C.), Harvard Forest (Mass.), and Howland Forest (Maine). The experimental sites represent the differences in the composition and productivity of Eastern U.S. forests.

“We will apply different models to these data,” Rahman says. “We plan to compare satellite to ground-based to airplane data, and see if there are discrepancies, and if there are, try to figure out why.

“This research will hopefully give us a better understanding of the carbon balance of Eastern U.S. forests, and the impacts of global change on these forests.”

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