From Glossary of Meteorology
A positively buoyant unmanned balloon attached to a cable that is used to raise and lower the balloon.
Instrument packages are suspended from the balloon to measure characteristics such as air temperature, winds, humidity, refractive index, trace gases, and aerosols as functions of time (by keeping the height constant) or height (by raising and lowering the balloon). They have been used for measuring both mean values and turbulent fluctuations. Balloon heights of over a kilometer have been reached, and instrument packages are sometimes deployed at more than one height below the balloon. Tethered balloons have been deployed from fixed locations over land and from ships.