Vaisala dropsondes: History, status, and applications

Vaisala has been the manufacturer of commercial dropsondes for many years, and was recently awarded a renewed five-year NOAA production contract for model RD94 dropsondes after an open bid process. Vaisala has also acquired the RD94 license from NCAR to provide the dropsonde to users outside the U.S. government. The experience for dropsondes has been gained in part from the design and manufacture of radiosondes since the beginning of Vaisala in the 1930s. Vaisala began co-operation in developing the RD94 with the National Center for Atmospheric Research, NOAA, and the German Aerospace Research Establishment (DLR) in 1994.

The current dropsonde RD94 sends temperature, humidity, pressure and GPS (wind speed and direction) data to the aircraft every 0.5 seconds, and weighs 390 grams. A drop from 20,000 feet (6.1 km) takes seven minutes as it descends while stabilized by parachute, although they can be operated up to an altitude of 24 km in both arctic and tropical environments. Dropsondes can be deployed at indicated airspeeds up to 250 knots.

The data acquisition system on the aircraft, AVAPS (Airborne Vertical Atmospheric Profiling System), collects two independent measurements per second and transmits the data in real time to users. AVAPS handles up to four dropsondes descending simultaneously, and is operated by one person.

The dropsonde is an integral part of the reconnaissance of tropical storms and hurricanes in the Atlantic-Gulf-Caribbean basin area. In addition several thousand Vaisala dropsondes are launched annually from more than eight countries in meteorological research and operational reconnaissance. Dropsonde data assimilated into numerical weather prediction models can lead to significant reductions in the position and intensity errors in model forecasts.