High-Flying Science, with Strings Attached - research with kites

Science News, Sept 16, 2000 by Sid Perkins

Beyond turbulence, mixing, and other physical phenomena in the atmosphere, Balsley says there's plenty of atmospheric chemistry that kites can help unravel. He's collaborated on various projects with John Birks, a chemist also at the University of Colorado at Boulder, and others to monitor atmospheric chemistry from Greenland to Peru.

Technology is making the job ever easier. In the early 1990s, Birks and his colleagues sent up flasks to collect air, which was later analyzed in a lab. Now, sophisticated electronic instruments can directly monitor ozone, carbon dioxide, water vapor, and other chemicals in the atmosphere and transmit the data to researchers on the ground.

Also, the scientists can now use a motorized tram that rides up and down the kite's tether to carry the instruments to specific altitudes, instead of winching the kite in and out to chase moving layers of turbulence or wind shear.

In August 1993, for example, Balsley, Birks, and their colleagues used kites to examine ozone levels over Cape Sable Island, which is near the southern tip of Nova Scotia. Sensors showed that ozone appeared at ground level in concentrations of 20 to 40 parts per billion. At altitudes between 300 and 500 m, however, the scientists measured similar concentrations during one test but 90 to 130 ppb 2 days later.

By checking weather patterns, Birks and his group showed that the air that passed over the site during the earlier period had originated over southeastern Canada. The scientists were able to trace the later air, with more ozone, back to heavily industrialized areas of the northeastern United States.

In another project, this one in the Peruvian Amazon in 1995, Birks and others took measurements revealing low concentrations of ozone over sections of virgin rain forest (SN: 8/10/96, p. 93). They also monitored the amount of carbon dioxide in the air. They're now conducting similar studies over the forests of northern Wisconsin and the Great Plains of Kansas and Oklahoma.

Kites provide surveillance of not only airborne chemicals but also the behavior of aerial creatures, such as the feeding frenzies of Mexican free-tailed bats. These bats, which migrate to their breeding caves in Texas each spring, serve as a brown, fuzzy 100-million-member Border Patrol that consumes about 2 million pounds of insects in a single night.

In the summer of 1997, researchers launched parafoil kites into the nighttime sky. Radiomicrophones were suspended beneath the kites at three different locations, each separated by 300 meters. This enabled the scientists to simultaneously eavesdrop at different altitudes.

Previous research with microphones suspended from free-floating balloons had revealed bats foraging at altitudes up to 750 meters, and ground-based radar had shown some bats and insects flying at heights approaching 3,000 m.

"Most people don't appreciate that insects fly that high or that bats feed on them there," says Gary F. McCracken, a professor of ecology at the University of Tennessee at Knoxville.