Weather device causes bomb scare

What goes up must come down.

That was the case Tuesday morning when a radio transmitter was found atop a cargo container at the State Ports Authority's Wando Welch Terminal.

It turns out that at least 200 of the devices are designed to go up and come back down every day. But it's not every day that one falls to earth and causes a bomb scare.

The transmitter was later identified as a radiosonde, a device roughly the size of a deck of cards that transmits data back to earth from a high-altitude weather balloon. Exactly where the transmitter touched down might never be known.

"It's a big old world out there, and this is a small thing," said Ken Goss, director of sales and marketing for Vaisala Inc. in Boston, the company that manufactured the radiosonde.

A truck driver spotted a suspicious item on a shipping container, prompting authorities to block access to parts of the Mount Pleasant terminal for about two hours. The Project Seahawk port-security task force; FBI; and Bureau of Alcohol, Tobacco, Firearms and Explosives all responded.

Authorities evacuated an area a couple of hundred feet around the truck and blocked all inbound and outbound terminal traffic. A bomb robot examined the device, which had an antenna and wires and batteries hanging off it, before technicians determined it was harmless.

The device measures weather conditions, including temperature, humidity and atmospheric pressure. It is attached to a helium-filled balloon that rises to an altitude of about 100,000 feet, or about 18 miles. Goss said it likely landed while the container was at sea.

The balloon transmits data on the way up, which takes about two hours. As the air pressure decreases, the gas inside the balloon expands. Eventually, the balloon pops and starts its descent back to earth.

The National Weather Service, the U.S. military, universities and other research organizations send balloons to the sky every day, mainly for weather forecasting, Goss said.

The transmitters are usually wrapped in foam and float back to earth on a parachute, said Greg Romano, a weather service spokesman. Often they're found with the strings and balloon attached, but only about 20 percent are recovered, he said.

The weather service alone sends up two of the balloons every day from 100 monitoring stations around the country, Romano said. It's not uncommon for law enforcement to be called when the radiosondes are found, he said.

As for images of the devices hurtling to earth like a comet, they fall at a velocity of only about 5 meters per second, or at about one-fifth of a mph. Not quite a bolt from the blue.

"But it would certainly surprise you," Romano said.

Reach Peter Hull at 937-5594 or phull@postandcourier.com.