Radiosonde, << RAY dee oh `sond,` >> is an instrument meteorologists use to take soundings (measurements) of the upper air. A radiosonde consists of devices that measure temperature, relative humidity, and air pressure, combined with a radio transmitter. The measuring devices and transmitter are in a small, lightweight box carried aloft by a balloon filled with helium or hydrogen.
The radio transmits the information recorded by the measuring instruments to ground stations. In addition, a radio direction finder tracks the radiosonde to determine the speed and direction of the wind at various levels of the atmosphere.
