History and Future of Dropsonde Technology Developed at NCAR

One of the most important research instruments for aircraft reconnaissance is the dropsonde. The National Center for Atmospheric Research (NCAR) has been developing dropsonde technology since the early 1960s and has supported airborne research and reconnaissance since its inception.

Early wind finding technologies used a transponder method, which allowed tracking up to 10 sondes simultaneously inside thunderstorms. The wind finding technology using the Omega global positioning system was developed at NCAR and was used starting in 1974 during the GARP Atlantic Tropical Experiment (GATE). Later, wind finding using the the LOng RANge (LORAN) global positioning system was developed at NCAR as well. In 1996, NCAR introduced the Airborne Vertical Atmospheric Profiling System (AVAPS), which uses GPS based dropsondes.

Historically, NCAR has used pressure, temperature, and humidity sensors from various suppliers. With the start of AVAPS, NCAR has cooperated with Vaisala and incorporated the sensor modules of the Vaisala RS92 and more recently of the Vaisala RS41 radiosonde into the dropsondes. Vaisala licensed the dropsonde technology from NCAR to produce and market the operational dropsonde with its current model RD41, which are used by NOAA, the US Air Force, and other users for hurricane observations and for airborne research and reconnaissance.

For the use on unmanned platforms, i.e. for the NASA Global Hawk and for long duration driftsonde balloons, NCAR has developed a smaller version of its dropsonde, the NCAR Research Dropsonde with its current version NRD41. This sonde can be launched through remote control using automatic launcher systems, which can carry up to 90 dropsondes. This dropsonde version is also used on the NCAR G-V and NCAR C-130 research aircraft.

Accurate analyses of the atmosphere state rely on accurate observations. NCAR and Vaisala have continuously optimized the sensor technology for dropsondes. In particular humidity observations, which have been challenging in the past, have reached a level, where measurements under almost all conditions within storms accurately reflect the atmospheric environment between G-V flight level and the surface.

With the introduction of the RD41 dropsonde model, many tests have been conducted in cooperation with NOAA and the US Air Force to guarantee the consistency of observations spanning the transition to the new dropsonde model. Future developments for dropsonde observations will include additional parameters, which are not yet measured, foremost sea surface temperature, and a network wide transition to the smaller NRD41 dropsonde.