The Vaisala Dropsonde RD94 is a general-purpose dropsonde for high-altitude deployment from a variety of aircraft. Slowed in its descent through the atmosphere by a special parachute, the RD94 measures the atmospheric profiles of pressure, temperature, relative humidity and wind from the point of launch to the surface.

The RD94 transmits meteorological data via a 400 MHz meteorological band telemetry link to the AVAPS receiving system onboard the aircraft. The AVAPS can be configured to track up to four RD94s simultaneously. The dropsonde and receiving system hardware and software have been developed at the Earth Observing Laboratory (EOL) of the National Center of Atmospheric Research (NCAR), in Boulder, Colorado, USA. Production of the RD94 and the AVAPS system is licensed to Vaisala Inc., USA.