radiosondes

Instrument packages containing a thermistor, aneroid barometer, and an electric resistivity hygrometer that measure the atmospheric vertical profile of temperature, pressure, and relative humidity, respectively. The battery powered measurements are simultaneously transmitted (using a radio frequency) to a ground-based receiving station as a helium-filled balloon carries it upward. Some of the larger models come with parachutes to lower it safely to the ground after the balloon bursts.