Science Fair Project Encyclopedia
A weather balloon is a scientific instrument which carries instruments aloft to send back information on atmospheric temperature , atmospheric pressure and humidity by means of a small, expendable radio transmitter. To obtain wind data, they can be tracked by radar, radio direction finding, or navigation systems (such as the satellite based Global Positioning System).
The unit that performs the actual measurements and radio transmissions hangs at the lower end of the string, and is called a radiosonde. Specialized radiosondes are used for measuring particular parameters, such as determining the ozone layer.
Before launch, the balloon is filled with helium or hydrogen gas. The rate of rise can be controlled by the amount of gas the balloon is filled with. Weather balloons may reach altitudes of 35 km or more, limited by diminishing pressures causing the balloon to expand to such a degree (typically by a 100:1 factor) that it disintegrates. The instrument package is usually lost. Above that altitude sounding rockets may be used.
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