radiosonde (rāˈdēōsŏnd) [key], group of instruments for simultaneous measurement and radio transmission of meteorological data, including temperature, pressure, and humidity of the atmosphere. The instrument package is usually carried into the atmosphere by a balloon (see weather balloon); balloon-borne radiosondes reach altitudes as great as 90,000 ft (27,400 m) above the earth's surface. A radiosonde may also be carried by a rocket, in which case it is known as a rocketsonde, or dropped by parachute (usually from an aircraft), in which case it is known as a dropsonde. Instruments included in a radiosonde are typically transducers for humidity, temperature, and pressure measurements; controls to improve return signals and determine which measurements are to be transmitted to data stations; and a radio transmitter. Radar also has been used to measure and transmit meteorological data from a radiosonde. These radiosonde observations are made as often as four times daily at some meteorological stations around the globe.