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. A rawinsonde is a simpler device intended for measuring wind speeds only. These measurements are taken by tracking the rawinsonde's position, so it does not need a radio link.

The device is tied to a helium or hydrogen 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 radiosonde communicates via radio with a computer that stores all the variables in real time. The first rawinsondes were observed from the ground with a theodolite, and gave only a wind estimation by the position. Modern radiosondes can use a variety of mechanisms for determining wind speed and direction, such as Loran, radio direction finder, and GPS. The most important variables measured by a modern radiosonde are:

• Pressure
• Altitude
• Geographical position (Latitude/Longitude)
• Temperature
• Relative humidity
• Wind speed and direction
• Some also give ozone concentration.

With the data, is possible to draw Stüve diagrams , which are useful for the interpretation of phenomena such as thermal inversion.

The weight of a radiosonde is typically 250 grams. A major manufacturer is Vaisala in Finland.