Montana State University

Green beam pokes into sky near MSU-Bozeman

October 21, 2003 -- by Annette Trinity-Stevens


A green laser beam used for taking atmospheric measurements disappears into the night sky above the Bozeman campus. (Photo by Joe Shaw)   High-Res Available

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A thin green laser beam, jabbing into the nighttime sky like an illuminated pencil, has nothing to do with UFOs or alien visits, said a group of Montana State University-Bozeman scientists responsible for the light.

Instead, the beam--about the color of Green River soda--is taking measurements of clouds, dust and other particles in the atmosphere.

Some Bozeman residents have caught sight of the green beam and followed it to its source behind Cobleigh Hall on the east side of the MSU campus. There, scientists Joe Shaw and Kevin Repasky have been switching it on at about 8 p.m. each Tuesday and Thursday for the last few weeks. They turn it off around midnight.

"You can see the beam from some distance," said Shaw, an associate professor in the electrical and computer engineering department. "You can see a green spot on the cloud, but there's no danger to people."

The laser beam is not safe if pointed directly at the eyes, however, so the team has to have Federal Aviation Administration approval to operate the laser. Pilots are warned against flying directly overhead while the beam is on. The group has FAA clearance to operate for a few more weeks and can apply for more time if needed.

The laser, bought from Big Sky Laser Technologies in Bozeman, sits on a wheeled cart along with a series of mirrors that project the beam through a long cardboard tube up into the sky. A telescope collects the light that scatters back, and a computer records the amount of backscattered light for each altitude.

The system is called LIDAR for light detection and ranging, similar to radar but using light instead of radio waves.

When combined with another instrument that records "night vision" pictures of clouds with an infrared camera, the LIDAR unit will gather a three-dimensional picture of what's overhead, Shaw explained.

It can show, for example, what kinds of clouds are in the sky and how warm, thick and high they are. The water vapor in clouds and other particulates like dust and smoke in the atmosphere affect climate worldwide, and federal agencies like the National Oceanic and Atmospheric Administration (NOAA) want more accurate data with which to build its climate models.

Currently NOAA uses satellites to monitor clouds from space, but ground-based measurements using LIDAR can be more reliable, Shaw said. That's especially true in snowy regions where in satellite pictures the clouds blend into the white ground cover.

Now that they know their LIDAR system works, the next step is for Repasky to build custom lasers that can be tuned to detect just how much water vapor or other particulates are present. A research assistant professor in the physics department, Repasky is working with AdvR of Bozeman on the tunable lasers and optical amplifiers. AdvR has funding from NASA for the project.

The group also wants to make the systems small enough to fit in a backpack. The hope is to build and sell the portable lidar systems in Montana, Repasky said.

Shaw and others also are experimenting with how to use LIDAR to count lake trout that are edging out the native cutthroat in Yellowstone Lake. Another project, done with the University of Montana, would use LIDAR to track bees trained to locate land mines.

Others involved in the LIDAR project at MSU include John Carlsten, a Regents professor of physics; Lei Meng, a post-doctorate student; grad students Mike Obland and Nathan Seldomridge; and undergraduate students Dusty Dunkle and Paul Nugent.

Contact: Joe Shaw, (406) 994-7261; or Kevin Repasky, (406) 994-6082