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UH Researchers Mapping Tahoe National Forest, Bit by Bit

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Toby Weber
A section of Honduran rainforest mapped by NCALM researchers. The center will use the same LiDAR technology to create a much larger map of the Tahoe National Forest.
A section of Honduran rainforest mapped by NCALM researchers. The center will use the same LiDAR technology to create a much larger map of the Tahoe National Forest.

Researchers with the University of Houston Cullen College of Engineering are creating what will likely be the most accurate and detailed map of a forested area the world has ever seen.

The map of Tahoe National Forest in California will chart every square meter of an area measuring 3,553 square kilometers (nearly 1,400 square miles), record the tree canopy height down to fractions of a meter and even identify the exact types of plant life in some areas.

The group creating it is UH’s National Center for Airborne Laser Mapping (NCALM), led by Ramesh Shrestha, Hugh Roy and Lillie Cranz Cullen Distinguished Professor in the civil and environmental engineering department. The group will generate the bulk of the map using LiDAR, or light detection and ranging.

The basics of LiDAR are simple: Fly over the area to be mapped with a system that shoots hundreds of thousands of laser pulses at the ground per second. How quickly those pulses hit the ground and bounce back to their source can be used to calculate the exact distance between the plane and the ground. Repeat that process several billions times times, and you’ve got a map.

The project in Tahoe is funded through a grant from the United States Forest Service to the University of California at Berkeley, which will essentially serve as the data’s curator. The lead investigator is Berkeley’s John Battles, professor of forest ecology and chairman of the ecosystems sciences division in the department of environmental science, policy and management.

According to Battles, the map will give Forest Service officials a one-of-a-kind baseline for understanding the forest and managing its resources and road networks.

On top of these practical benefits, such a LiDAR map will be a huge benefit to ecological researchers. In typical forest studies, Battles said, a dense study plots just one percent of the ground. With LiDAR, essentially 100 percent of the area is charted, allowing researchers to conduct otherwise impossible research.

“In this case, quantity is its own quality. We’ve never had the capacity to do these kinds of analyses,” said Battles. “Say you’re interested in invasive species spread. One of the key drivers of this spread are trails, rivers and road networks. Some of these you just don’t have enough spatial scale to analyze. This project will let us see all these networks and all the habitat patches and how they relate.”

That’s just one project, he noted. The maps generated by this effort will immediately be made available to any researcher who wants them, which should result in a number of research projects large and small. Some possible topics include:

  • Analyzing the effectiveness of land treatments designed to prevent major forest fires – a project Battles himself will undertake;
  • Identifying habitats of rare or endangered species and analyzing how they relate to features such as roads and trails; and
  • Calculating the amount of carbon sequestered by the forest’s plant life.

LiDAR isn’t the only mapping technology the researchers are using on this project. In some areas, they’ll also perform hyperspectral imaging. This aspect of the project, led by assistant professor of electrical and computer engineering Saurabh Prasad, will allow the researchers to generate and analyze images using not just light from the visible parts of the electromagnetic spectrum, but also those parts that cannot be seen with the human eye, such as near infrared and short-wave infrared.

Since different plants have different signatures in this part of the spectrum, such information can be used to determine the exact types of plants and trees found in an area. And because certain plants play a specific role in the lives of certain animals, hyperspectral imaging will help researchers understand Tahoe’s animal life too, Battles said.

For NCALM’s Shrestha, the research opportunities this map will open up are in perfect alignment with his group’s mission. NCALM is not just a home for original research; it’s also intended to serve as a resource to investigators from other disciplines and other institutions.

“By creating incredibly detailed maps, we’ve been able to help researchers in archeology, ecology, engineering and many, many other fields,” Shrestha said. “The Tahoe project is our biggest effort yet and the maps it creates will be available to anyone who wants them. I’m looking forward to seeing how researchers use this data in the years to come.”

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