New Green beam's new shape

Upgrades for USU lidar to measure haze
By Arrin Brunson
The Herald Journal
November 26, 2002

The green beam of light that will occasionally be visible in the night sky above Cache Valley is not part of a publicity gimmick to draw potential customers to a "Huge Closeout Sale."

The laser light emanating from the new Calibration and Optical Research Lab at the Utah State University Innovation Campus in North Logan is actually a research tool. Currently, the laser beam can be seen as a vertical green beam at night. Soon the laser light, known as a lidar, will be sweeping the sky above Logan in a conical pattern.

Project manager and USU research professor Tom Wilkerson said via e-mail correspondence the AROL-2 lidar atop the building's observatory detects the passage of clouds and aerosols over Cache Valley by sending out short pulses of laser light that are then scattered back to the lidar's telescope by layers of dust, haze and clouds.

Scientists will use these pictures to define the altitude of clouds and the thickness of haze layers, Wilkerson said, which will generate data regarding local air quality.

"We will be able to monitor the haze in Cache Valley during inversion periods this winter, and will be prepared to detect clouds of dust from United States and Asian deserts when they reach us here," he said. "At present this lidar detects mostly atmospheric particles called aerosols such as dust, fine water droplets in haze and clouds, and ice crystals in high altitude clouds (cirrus clouds and aircraft contrails)."

Planned modifications will allow the scientists to detect the molecules of clear air and aerosols in the stratosphere, Wilkerson said. The new Observatory space, featuring six roof hatches, eight viewing windows, two separate viewing rooms, and roof access, is ideal for this work, he said.

With video records of cloud motion, AROL-2's altitude pictures are used to measure the wind at cloud altitude. Scientists have been working jointly with NASA scientists from Goddard Space Flight Center, who measure winds by different methods, according to Trina Paskett, public relations specialist at the Space Dynamics Lab. The first year of the joint campaigns with NASA was funded by an internal SDL Enabling Technologies grant, she said.

The goal is to develop several "remote sensing" methods to measure winds and how they vary with altitude, without having to fly weather balloons, a technology that may someday be developed for use in satellites, Wilkerson explained. With this, the world's meteorologists can see, on a daily basis, the global pattern of winds for improvements in weather forecasting.

A vital part of this lidar project is the role of students who not only carry out and interpret the measurements but also develop new, original methods and theories for observations. Besides Dr. Wilkerson, there are five engineering undergraduate students working on various aspects of the work: Mark Anderson, Ionio Andrus, Scott Cornelsen, Cameron Egbert, and Garrett Wheeler. The project began in 1999/2000 with a master's degree student in Physics, Jason Sanders. In addition to several published papers on the project's results, a related patent application has been filed by Wilkerson, Sanders and Andrus.

The observatory is a controlled space that will also be used to test and calibrate optical instruments, Paskett said. SDL will be able to make ground-based observations of the sky at the same time that satellite instruments look down on Utah from space.

The observatory floor consists of a 12-inch thick concrete slab in the enclosed area with an additional 2 inches of foam and 4 inches of concrete on the outside areas, and 12-inch thick concrete block support walls. This solid structure minimizes vibration when sensitive optical equipment is in use. In addition, SDL will use the Observation Deck to make detailed nighttime tests of new instruments prior to their use here or at other sites around the world.