Md. laser tests may help in global warming battle

UM, NASA scientists hope system can measure effects of deforestation

September 25, 1999|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

Laser beams fired from the skies over Central Maryland this weekend may lead scientists to better ways of fighting global warming, protecting old-growth forest and even forecasting the weather.

At the laser's trigger will be University of Maryland and NASA scientists, flying aboard a four-engine NASA C-130 airplane based at NASA's Wallops Flight Facility on Virginia's Eastern Shore.

Weather permitting, they will be flying at 20,000 feet, sweeping their laser's 75-foot-wide beam across state forest lands, along the Patuxent River from Bowie to Mount Airy, and possibly the Patapsco River west of Baltimore.

If the tests go well, the laser light will bounce back to detectors on the airplane and reveal the height and age of the trees below, as well as the amount of carbon they contain.

It's a promising remote-sensing technology that forest ecologist Robert G. Knox and the instrument's inventor, J. Bryan Blair -- both of the NASA Goddard Space Flight Center in Greenbelt -- hope to test and improve with these flights over well-studied forests in Maryland and elsewhere.

They plan to put the same technology into orbit for global forest measurements, beginning with a satellite launch next September from a new NASA launch facility in Alaska.

"We have no accurate idea of what the biomasses of the Earth's forests are," said Ralph Dubayah, an associate professor of geography at College Park and the project's principal investigator.

Biomass is the mass of matter that makes up living things. If they knew the biomass of a forest, scientists could calculate how much carbon its trees contain. That would tell them how much would be released into the atmosphere as carbon dioxide -- a "greenhouse" gas that plays a key role in global warming -- if the forest were cleared and burned. The world loses about 50,000 square miles of tropical forests a year.

Satellites with optical sensors are already flying over the planet, monitoring man's destruction of the Earth's forests. NASA has flown similar missions using radar-mapping technologies aboard the space shuttle. But Dubayah said neither the optical nor the radar devices can yet accurately determine how tall the trees are, or how much carbon is locked up in the trunk, leaves and branches between the forest canopy and the ground.

"Our best estimate of the carbon we're adding from tropical deforestation is 1.6 gigatons per year," he said. A gigaton is one billion tons. "But the uncertainty is at least a gigaton. So we could be adding 3 gigatons a year."

That's huge. All the fossil fuels burned each year in the world pump an estimated 5.5 gigatons of carbon into the air.

Without a more precise measure of the carbon entering the air from deforestation, Dubayah said, "we don't know what actions we should take to combat that."

"Lidar," or laser altimetry, he believes, may provide the more accurate numbers scientists need.

Lidars fire short pulses of light at the forest canopy. Beamed down from an altitude of nearly four miles, the light poses no danger to people on the ground, the scientists said.

But by measuring the time it takes for the light bounce off the ground, and the treetops, and return to the airplane, scientists can calculate the distances, and compute the height of the trees.

Even better, Goddard's airborne Laser Vegetation Imaging Sensor (LVIS) can record the shape, or waveform, of the returning signal and from that determine the concentration of mass between the canopy and the ground -- the trunks, branches and leaves.

The LVIS system is being tested in flights yesterday over forests in North Carolina, and today in Maryland and New Hampshire.

The Patuxent watershed was chosen because it is laced with 20 to 30 research field sites. Dubayah and his College Park students have gathered detailed information about the forest cover there. Similar measurements have been done at the other eastern and West Coast study sites.

Next September, a more complex version of the LVIS technology, called Vegetation Canopy Lidar (VCL), will be launched into orbit on a two-year mission to map and measure the biomass of nearly all the Earth's forest cover.

The NASA/University of Maryland mission is scheduled to be the first ever launched from NASA's new Kodiak Launch Complex in Alaska. The satellite will eventually cross 99 percent of the planet's forests.

The spaceborne lidars will aim five laser beams at the ground. The five, 75-foot-wide beams -- spaced one mile apart -- will sample forest data across a path four miles wide. The results will be averaged to characterize the entire forest.

The orbital mission will be run from a College Park control room manned by professional staff and graduate students. The entire operation -- from development to launch and production of the data -- is budgeted by NASA at $60 million.

In addition to the forest biomass data, Dubayah expects the VCL mission will provide meteorologists with more detailed information on the Earth's surface "roughness."

"If you have a rough surface with a lot of trees, we know it will slow the wind down," he said. "You need to be able to accurately predict wind speeds over the land's surface to produce accurate weather and climate forecasts." Different forest covers will also produce varying evaporation rates important to forecasting.

Better maps of the age and three-dimensional structure of forests could also help wildlife managers.

"If you don't have sufficient sub-canopy airspace between the last branches and the ground, you may have limited habitat for some types of birds," such as the goshawk, Dubayah said.

Pub Date: 9/25/99

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