A radiosonde is a unit for use in weather balloons that measures various atmospheric parameters and transmits them to a fixed receiver. A frequency band at 403 MHz is reserved for radiosondes.
The device is tied to a helium filled balloon, which lifts the device up through the atmosphere. The balloon bursts at about 30000 meters due to lack of external air pressure at that altitude. The modern rawinsonde communicates via radio with a computer that stores all the variables at real time. The first rawinsondes were observed from the ground with a theodolite, and gave only a wind estimation by the position. The most important variables measured by a modern radiosonde are:
Thus, rawinsonde observations of the atmosphere describe the vertical profile of temperature, humidity, and wind direction and speed as a function of pressure and height from the surface to the altitude where the sounding is terminated.
The synoptic rawinsonde observing programs of the United States and the other WMO member countries are designed to meet real-time operational needs for weather analysis and forecasting.
Rawinsonde observation data are applied to a broad spectrum of operational, climatological, and research efforts.
By tracking the position of the radiosonde in flight, information on wind speed and direction aloft is also obtained.
Observations where winds aloft are also obtained are called "rawinsonde" observations.
The radiosonde flight can last in excess of two hours, and during this time the radiosonde can ascend to over 115,000 feet (35,000 m) and drift more than 125 miles (200 km) from the release point.
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