The Global horizontal sounding technique (GHOST) program was an atmospheric field research project for gathering weather data with balloons. Unlike radiosonde balloons which collect vertical atmospheric sounding data over the release point during a relatively short ascent lasting a few minutes, horizontal sounding balloons stay aloft for much longer periods lasting several weeks or months, floating at a predetermined altitude. The GHOST program studied the movement of upper-air currents and tested the feasibility of using horizontal sounding techniques to provide the necessary weather observations for very long-range global scale numerical weather prediction.[1] The GHOST project was part of the Global Atmospheric Measurements Program (GAMP). Eighty-eight GHOST balloons were launched in a 10-year period[2] starting in March 1966.[3]
The GHOST design used a superpressure balloon with an aluminized PET film envelope holding the gas inside at a higher pressure than the surrounding atmosphere, allowing it to maintain a nearly constant altitude. These gas balloons float at a constant density altitude,[2] where the balloon displaces a mass of air equal to its own, and are not affected by solar heating and subsequent expansion of the lifting gas as in a zero-pressure balloon.[1] This makes them suitable for studying atmospheric motions at a constant pressure level above the surface.
The electronics payload was suspended below the balloon on a tether that also acted as a high frequency band radio antenna. The GHOST payload included a sun angle sensor that varied the repetition rate of its Morse code radio signal to allow technicians on the ground to locate it using an HF receiver and a set of sun angle tables.[1]
On September 29, 1968 a 10-foot (3-meter) GHOST balloon at an altitude of approximately 52,000 feet (16,000 meters) completed a full 365 days in flight, becoming the first balloon to fly for a full year.[1] This record-breaking balloon, launched from Christchurch, New Zealand by the U.S. National Center for Atmospheric Research (NCAR), continued to fly for an additional 76 days, completing 35 circumnavigations of the Earth. The longest flight of the program was 744 days, or just over two years. The balloons could not be flown in the Northern Hemisphere because the Soviet Union would not permit overflights at the time.[3]
Vincent E. (Vin) Lally of NCAR received the Otto C. Winzen Lifetime Achievement Award from the American Institute of Aeronautics and Astronautics in 2003 for his pioneering work in the application and development of superpressure balloons for worldwide atmospheric measurements, including the GHOST program.[4][5] Winzen was a pioneer of modern ballooning, and this award recognizes outstanding contributions to the advancement of free-flight balloon systems or related technologies.