A radiosonde (Sonde is German for probe) is a unit for use in weather balloons that measures various atmospheric parameters and transmits them to a fixed receiver. A radio frequency of 403 MHz is reserved for radiosondes, although they can be adjusted up to 406 MHz as required. 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 maximum altitude the balloon ascends to is determined by the size of the balloon, or weight of the balloon material. Balloon sizes can range from 150 grams to 3000 grams. An 800 gram balloon will burst at about 30,000 meters (about 100,000 feet) 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, GPS and (in Canada only) Very low frequency. 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, it is possible to draw a Stüve diagram or a Skew-T log-P diagram; both of which are useful for the interpretation of phenomena such as thermal inversion.

Radiosonde data are an important component of numerical weather prediction. Because a sonde may drift several hundred km during the hour and a half of flight there may be concern that this could introduce problems into the analysis; however, this appears not to be so except perhaps locally in jetstream regions in the stratosphere ^*.

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

In 1985 the Soviet Venus probes Vega 1 and Vega 2 each dropped a radiosonde into the atmosphere of Venus. The sondes could be tracked for two days.

External links

• Current raw upper air data for most of Canada and the United States
• WMO spreadsheet of all Upper Air stations around the world
• Interpreting radiosonde data Tephigrams and Skew-T log P diagrams.
• NOAA National Weather Service Radiosonde Factsheet

Measuring instruments | atmospheric thermodynamics | Meteorological instrumentation and equipment

Radiosonde | Radiosonda | Radiosonde | ラジオゾンデ | Radiosonda | Radioluotaus | 无线电探空仪