The National Weather Service wants its radiosondes back.

Twice a day these automated data-gathering devices are released from about 100 sites around the country and carried by large helium balloons to as much as 20 miles above the ground. As they climb, radiosondes broadcast information on temperature, winds, air pressure and humidity to weather service ground stations.

When the device gets high enough, the diminished air pressure allows the helium to burst the balloon and a paper parachute emerges to slow the light-weight radiosonde's plunge back to the ground.

Each one costs $54, and the weather service has traditionally relied on helpful citizens to find many of them and mail them back for reuse, a practice that has typically returned about 18,000 radiosondes a year and saved taxpayers about $10 million over the last 40 years.

In recent years, however, fewer and fewer radiosondes have been making it home again. "The increased use of new units is driving up our costs," says Richard E. Halgren, head of the weather service. Halgren has launched a drive through various farm and outdoor organizations to encourage people to return radiosondes.

The devices, about the size of a shoebox, are white and covered with weather-resistant plastic and cardboard. Each contains a prepaid mailbag with instructions. You can keep the parachute.