By Kathryn Summers

On most clear nights in Logan, there's something to see in the night sky besides the stars and moon.

Most people living in or near Logan are familiar with the green beam that shoots up into the sky from the Utah State University campus. However, the purpose of this green beam is a mystery to many.

The beam is called lidar, which stands for LIght Detection and Ranging. It is like radar except it uses light, said Karen Nelson, a student research assistant in the Atmospheric Lidar Observatory.

The observatory, part of the Center for Atmospheric and Space Sciences, is in USU's Science and Engineering Research building. The lidar is also supported by the National Science Foundation, according to the CASS website.

Lidar is used to study and categorize atmospheric dynamics and how things change over time, said Nelson. In the long term, the information gathered at USU will add to the general knowledge of climatology.

The lidar is made up of a powerful Nd:YAG laser, a telescope 44 cm in diameter, and a sensitive detector for the laser light coming back from the sky, according to the CASS website. The beam of light is sent up into the sky. Light bounces off particles in the air, and some comes back to the observatory where it is collected by the telescope and then analyzed.

Although it appears to be a continuous beam of light, the laser emits 30 pulses per second, the same rate a television screen is refreshed. The laser is 17 watts of polarized light concentrated into an area the size of a quarter. Even though the beam appears to bend, it shoots straight up into the sky, said Nelson.

The beam is used to study the middle atmosphere, from about 50 to 90 kilometers above mean sea level said Nelson. Planes and weather balloons can measure the air below, and satellites and rockets measure the air above.

This middle zone, the mesosphere, is harder to measure, and lidar is one the best methods.

"Trends for the atmosphere show up more quickly and more dramatically in the upper atmosphere," said Nelson. That's why the mesosphere is an important section to study. In the study of global warming, for every degree the Earth warms up the mesosphere cools 3 degrees.

In order to get better data, the observatory is building a bigger telescope. The new lab will be on the third floor of the SER building. When the new system is finished, lenses will be used to send the green beam in other directions besides straight up. This will allow the scientists to measure the Doppler shift, which will tell how fast the air the light bounced off from was moving. The new lidar system will be able to measure wind and temperature in the mesosphere.

-- For more information see these websites:

http://control.cass.usu.edu/lidar/index.htm

http://pcl.physics.uwo.ca/

http://www.misty.com/~don/laserssl.htm#ssllrr

JL
JL

September 1998
October 1998

January 1999
February 1999
March 1999
April 1999
September 1999
October 1999
November 1999
December 1999

January 2000
February 2000
March 2000
April 2000
May 2000
June 2000
July 2000
August 2000
September 2000
October 2000