Robert Brown|Balloon shoot-down has U.S. on alert. Weather forecasters know how to steer clear

Balloon concerns have Robert Brownthe U.S. military now looking at a lot of what an assistant secretary of defense has called "low speed clutter" in America's skies.

The National Weather Service, which launches about 184 balloons every day across the country, says they make sure they and aviation authorities know where all of them are at all times.

These balloons allow weather forecasters to predict upcoming trends and future storms. Some even give researchers measures of pollutants. And to make sure their balloons aren't mistaken for clutter, the National Weather Service uses a GPS to track each one and notifies the Federal Aviation Administration before each launch – many of which take place at airports.

"Balloons were one of the first tools used to collect environmental data, dating back to the 1700s," National Weather Service spokesperson Susan Buchanan says. "Our balloons provide valuable atmospheric data used to produce weather forecasts."

So far, all National Weather Service balloons have been accounted for, according to Buchanan.

"None of the objects that were shot down were NWS balloons, as none of our balloons are missing," she says.

Protecting National Weather Service Balloons

The U.S. has shot down three unidentified aerial vehicles since Feb. 4 – in addition to a balloon the State Department says is part of a "fleet" of Chinese military balloons. One of the remaining unidentified aerial vehicles was shot down because of potential surveillance concerns, while the remaining two were seen as threatening to civilian flight in the U.S. and Canada.

The possibility of the United States shooting down more unidentified aerial vehicles hasn't spurred much concern at the National Weather Service.

That's because they communicate with the Federal Aviation Administration before each launch – on top of GPS tracking each balloon once it drifts into the sky.

"Most of our upper air balloon launch sites are co-located with airports. For these sites, we call the FAA tower before we launch our morning and evening balloons," Buchanan says. "Some others that are not located near airports (Miami is an example) also call the local FAA tower before each launch."

The National Weather Service also tries to keep the public informed of its launches and teach about the balloons.

"We use every opportunity to provide public outreach and education about our balloons," Buchanan says. "We particularly focus education on what to do when the public finds a radiosonde that has parachuted back to earth so they aren't alarmed by it."

A radiosonde is an instrument that measures temperature, pressure and relative humidity amid extreme cold and nearly 200 mph winds.

National Weather Service Balloons

Composed of latex and synthetic rubber, National Weather Service balloons are filled with helium, and expand as they ascend to almost 100,000 feet – growing from six feet in diameter to about 20. Once in the air, the balloons can travel as far as 125 miles over the course of about two hours.

And the process of tracking radiosondes can send even more information to the ground, says Russell Dickerson, a professor of atmospheric and oceanic sciences at the University of Maryland who has participated in launches.

"As they drift with the wind, the location is radioed back to the Earth's surface and we can determine the winds," he says, noting that launches led by people and organizations outside the National Weather Service are also responsible for notifying the Federal Aviation Administration.

Once the balloons burst, a parachute gently sends the radiosonde back to Earth. These cheap packages, he says, are smaller than a large bird and are "basically throwaways," designed to not damage airplanes if there's a collision.

Around the world, forecasters launch balloons from about 900 locations that "give us a synopsis of the weather on a global scale," and some even measure smog and pollution, according to Dickerson.

In addition to regular weather balloons, there are other types of balloons in the sky that examine the upper atmosphere and stratosphere, which extends from about 6.2 miles to about 31 miles. But they're "usually announced well in advance," Dickerson says.

There are also balloons launched by NASA that measure ozone, which protects the Earth from above but is also a greenhouse gas closer to home.

"[Ozone] has a good side and bad side, like the force," says Dickerson, who says he would hate to see those balloons destroyed. "It's good up there, but not down here."