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Monitoring the ecosystem in 3-D
Digital Government esearchers test stereoscopic mapping technologies with broad implications for biodiversity studies
DGRC Staff

Digital Aerial Video Mosaics

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" Creating free mosaics
" UMass Computer Vision
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image - overflight diagram

The team is researching methods of determining the health of forests through a marriage of ecosystem modeling and digital aerial photogrammetry.

Over the last 25 years, the emerging technologies of remote sensing and advanced data processing have transformed the ancient art of mapping.

Sending multispectral scanners into space, the National Aeronautics and Space Administration has developed many-layered maps of striking clarity and precision that, in some cases, have replaced the painstaking work of aerial photographers and land surveyors, at a fraction of the time and cost.

The nascent mapping technologies provide a new standard for land classification. The human eye cannot see the detailed nuances of the light spectrum. Across the entire spectrum, however, different objects reflect sunlight in different ways; these differences are said to give each material a "spectral signature."

By designing cameras to record these signatures, mapmakers can plot with precision complex biological mixes on the ground. At the same time, orthographic images, corrected for the topographic distortion created by the geometric angle between the airborne camera and the ground, data compression, geographic information systems and other advances have made for even more detailed mapping information.

But NASA's satellite images are on a grand scale that is not always suited to land-based scientific and government projects. The images typically have insufficient resolution for many applications, their coverage may be limited, they often are obstructed by clouds, and researchers cannot control their timing. At the same time, conventional aerial photography is expensive and requires heavy training.

Under a National Science Foundation Digital Government small business grant, Howard Schultz, senior research scientist at the Computer Vision Laboratory, University of Massachusetts, Amherst, has been developing a general interest commercial instrumentation terrain mapping system.

Potential government customers for the system - developed with a Digital Government grant and an SGER grant, include the USDA Forest Service, the Environmental Protection Agency and the Department of Defense, he said.

The system, under the aegis of Schultz's technology transfer company, Aerial Vision Inc., consists of:

  • A digital camera, which takes overlapping, multi-spectral images as the plane flies along
  • A global positioning system that gives the exact position of the airplane when each image was snapped
  • And an attitude and heading reference system that records the exact direction in which the camera is pointing.

Designed to be cheap, efficient and user friendly, carried by a low-flying plane, the system produces very high-resolution layers, including a multispectral image and a 3-D elevation map of the terrain, Schultz said.

"We plan to build a system that requires little or no processing of the data after landing," Schultz explained.

Now Schultz and a team of collaborators hope to expand the work to take on scientific and government issues on a heroic scale, including global warming, greenhouse gases, sustainable farming and forest management.

Their propoal, under review by the National Science Foundation, is an ambitious government-scientific partnership, including teams from the University of Massachusetts, Amherst (Howard Schultz, Edward Riseman, Allen Hanson); Mount Holyoke College (Thomas Millette); Winrock International, a non-profit resource management organization to help the world's poor (Dana Slaymaker); Harvard University (Julian Hadley and David Foster); Duke University (James Clark,), and the USDA Forest Service (Dave Hollinger and James Vose).

"This project requires development of new computer science algorithms that enable environmental scientists from the USDA Forest Service, Harvard and Duke to extend their work to large tracts of land," Schultz says.

The goal is to produce detailed maps of forests that show attributes such as the biomass, health, and species of forests, down to the individual trees, and be able to track changes from year to year, and season to season, Schultz said. "We need to have very accurate maps to find the exact same trees next year, and see how healthy, how fast-growing they are, and do they have disease," he said.

"Right now only few trees, in a limited area, can be measured by hand. Or if you look at satellite images, the data's too coarse to see individual trees." One of the most important advantages Schultz is designing into the system is its 3-D capability. Reproducing the actual shapes of rocks, hills and trees gives a far more accurate view of the terrain that is essential to cutting-edge research.

Viewable Stereoscopic Pair

image - overflight diagram

Two images of a forest canopy can be combined into a single three-dimensional image. This allows environmental scientists to gauge the health of entire forests at an extremely fine level of detail - even monitoring the growth and death of individual trees.

"What we want to do is fly an airplane and from the air do what people have been doing laboriously on the ground," Schultz said. "This is made possible because digital cameras are easier to use, and take much higher resolution images. It's just now reaching that point."

David Hollinger, scientist with the Forest Service's Northeast Research Station in Durham, New Hampshire, is in the woods of Howland, Maine, studying the role of forests in the carbon cycle.

The government has very good figures on the amount of carbon burned by industry and public agencies, Hollinger said. Fairly recently, however, scientists were surprised to learn that only half the carbon dioxide released in the burnoff goes into the atmosphere. The rest is removed by forests and oceans, he said. Some forests, with new, fast-growing trees, are net carbon intakers, while others expel carbon, Hollinger said.

Less well understood is how to best manage the forests to reduce carbon dioxide emissions, thus slowing greenhouse warming and acid rain, he said. Precise data, down to the type and number of trees, and growth figures from year to year, will help, he added.

"Satellite images come in months later (and) the scale is very large," Hollinger said. "This way, we can get data any time in the way we want it."

James Vose works as principal investigator at the Coweeta Hydologic Laboratory in the southern Appalachian Mountains of North Carolina, a working forest in steep hilly country, with lots of rainfall, and mixes of hardwoods, pine and spruce on the ridges, hemlock along the streams.

"It's about as good as it gets here," Vose said of his environment. The focus of the lab is watershed ecology. His chief interest is forest canopies, their spatial and species distribution, and how they influence water and carbon cycling.

His research could help scientists understand the effects of such hot-button issues as tropical deforestation, acid rain and tree disease, he said. But until now, canopy measurements were taken strictly by foot-slogging manual surveys.

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"We have to do it using manual measurements, and there are limits in the amount of area in a watershed you can measure," Vose said. "This remote way would allow more watershed to be characterized, more complete sampling. I'm pretty excited about this, because if it works, one of hardest things to characterize is spatial variation in the canopy. It requires such intensive sampling.

"Any disturbance that affects the canopy - tropical deforestation, acid rain, insects and disease - could all be monitored and indexed with this technology," Vose said. "It would be a significant advance. In 30 to 40 years studying the canopy, there never have been any large-scale measurement advances like this."