Kevin Nolte, age 15, of Nashua, N.H., for his question:

WHAT IS RADIOSONDE?

A radiosonde is an instrument used by meteorologists to take soundings or measurements of the upper air. A radiosonde consists of devices that measure temperature, relative humidity and air pressure, combined with a radio transmitter.

You pronounce the word RAY dee oh sahnd.

The parts of a radiosonde are enclosed in a small, lightweight box that is carried into the air by a balloon filled with helium or hydrogen.

The radio transmits the information recorded by the measuring instrument to ground stations. In addition, radio direction finders track the radiosonde to determine the speed and direction of the wind at various levels.

This information is computed by measuring the elevation angle and direction of the radiosonde while the balloon is ascending at a known rate of speed.