Around the world each day balloons equipped with radiosondes make more than 1,000 different measurements of the wind, temperature, pressure, and humidity in the upper atmosphere (see Meteorology). These flights are made almost exclusively from land areas. As a result, measurements of the atmosphere are made over less than 20 percent of the globe. To obtain coverage over ocean areas, Global Horizontal Sounding Technique (GHOST) superpressure balloons have been flown experimentally from the Southern Hemisphere. These balloons fly with the winds, and their locations provide essential data about winds in the stratosphere above the oceans. The first flight around the world with a GHOST balloon was launched from Christchurch, New Zealand, in 1965 by a team from the National Center for Atmospheric Research (NCAR), based in Boulder, Colorado. The longest flight, floating at an altitude of 14 km (9 mi), lasted 744 days, circling the Earth more than 50 times.
Zero-pressure balloons, some as large as 150 m (500 ft) in diameter, carry scientific payloads of several tons to stratospheric altitudes. They are used in a variety of scientific applications. For example, such balloons can provide a platform for telescopes or radiation sensors to operate above the interfering atmosphere. Or they can act as a carrier for on-site measurements at altitudes higher than the capabilities of powered aircraft.
Zero-pressure balloons flying above 30 km (20 mi) are a useful platform for astronomical observations with infrared telescopes. Water vapor in the lower atmosphere interferes with viewing through infrared telescopes, but at an altitude of 30 km, water vapor is not a factor. Infrared telescopes have become essential in resolving such questions as the origin and nature of the universe, the birth of stars, and the physics and chemistry of interstellar matter. Cosmic rays, gamma rays, and high-energy X rays have also been studied from the high-flying, zero-pressure balloon platforms.
Zero-pressure balloons are an essential instrument for helping scientists understand the interactions between industrial chlorofluorocarbons (CFCs) and the stratospheric ozone layer, which absorbs harmful ultraviolet radiation from the Sun. Scientists believe that CFCs are destroying Earth’s protective ozone layer. Balloons provide the only platform capable of measuring the interactions between CFCs and ozone in this region 19 to 48 km (12 to 30 mi) above the Earth's surface.
Balloon platforms offer a low-cost alternative to satellite observations, but are limited by only one or two days of viewing because the measurement instruments are heavy and restrict the amount of ballast that can be carried. In the late 1990s the National Aeronautics and Space Administration (NASA) began a major effort to develop a superpressure balloon capable of carrying a 2,000 kg (4,400 lb) payload to an altitude of 40 km (25 mi) for up to 100 days. The Ultra-Long-Duration Balloon Program (ULDB), as the effort is called, requires the development of new film structures capable of handling the stresses of extended, high-altitude flight with heavy payloads. If this capability is realized, the balloon may become a low-cost alternative to some types of satellites.