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26 March 2004

Tracking sunlight, ozone and haze across the USA

by Forrest M. Mims III

When students and professors at Texas Lutheran University (TLU) in Seguin, Texas, returned from their spring break, some of them noticed that something new had been added to the roof of the Moody Science Building.

Perched high on the parapet on the south side of the building is a strange array of new instruments. Most rooftop science instruments don't appear very busy, but these certainly do.

They'll probably attract quite a few stares in coming days, as students try to figure out what they are and what they are doing.

Every 15 seconds, curved metal arcs less than the diameter of a volleyball rotate into view. They pause three times in the air over each of the instruments before dropping out of sight.

These instruments are called shadowband radiometers. Their purpose is to measure sunlight coming directly from the Sun and also from the sky. They measure various colors of sunlight, the ozone layer, haze and water vapor.

Other instruments at the TLU site measure the UV-B that causes sunburn and blue and red colors of sunlight that make plants grow. Temperature and relative humidity are also measured.

The instruments were installed at TLU during spring break by William Durham and Roger Tree, both researchers at Colorado State University. Thomas Dodgen, TLU's Director of Physical Plant, and his staff provided important assistance. The project was approved by TLU's Dr. John Sieben.

TLU is now the thirty-first site in the United States Department of Agriculture (USDA) UV-B Monitoring and Research Program. The program is headed by Dr. James Slusser, a well-known authority on both solar ultraviolet and air pollution.

The USDA UV-B network forms a grid across the United States, with sites also in Alaska, Hawaii and Canada.

The TLU site fills a major void in the network. Now scientists will be able to track UV levels from Big Bend to Louisiana. They will be able to find out how the ozone layer, air pollution and clouds affect UV.

They will also be able to track major dust, smoke and other air pollution events as they move across this area from adjacent States, Mexico, Africa and Asia.

I've been making UV-B measurements just north of Seguin since 1989. But the USDA measurements are better, because they are made all day at three minute intervals.

The data are automatically sent to Colorado State University every night and made available on the World Wide Web by the next morning.

In future columns I'll explain more about these instruments and how they are a major asset for student research projects at TLU and local schools.

Meanwhile, for more information about the new TLU instruments, visit the USDA UV-B Monitoring and Research Program web site at http://uvb.nrel.colostate.edu/UVB/home_page.html.

Forrest M. Mims III is the site operator for the new USDA instruments at TLU. His science is featured online at http://www.forrestmims.org/.

This feature was originally published in Forrest Mims's weekly science column in the Seguin Gazette-Enterprise, Seguin, Texas. The column is written for a general audience.