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The following information is taken from Lally, V. E. 1985. Upper air in situ observing systems. Handbook of Applied Meteorology. David D. Houghton, editor. John Wiley & Sons, Inc. 352-360.
Balloon designs have evolved for different research purposes and desired flight patterns. Constant-level balloons, such as super-pressure balloons, zero-pressure balloons and tethered balloons are examples of designs developed for meteorological purposes. Made from natural or synthetic elastics, intended flight duration and altitude defines balloon selection. Balloons and balloon payloads are subject to aviation regulations and limits because they pose hazards to aircraft. Although balloons are not long-lived platforms, elements that create particular problems for them are ice and frost, pinholes, and ultraviolet damage.
Document Type: Platform Document
Revision Date: December 1995
Upper air observations are performed at mandatory and significant levels set by the World Meteorological Organization. Prior to 1946, observations were made at constant heights, now they are taken at constant pressure surfaces. Data reported in the Historic Arctic Rawinsonde Archive, include twice daily observations of as many as 20 to 40 mandatory (e.g. surface, 1000 mb, 850 mb, 750 mb, 500 mb) and significant levels.
No one management can be named. The data are compiled from five original archives, beginning as early as 1948. Sources are:
Data is collected for climatological and weather forecasting purposes.
Lally (1985) describes several types of balloons used for making upper air observations. The following is a general description from "Upper air in situ observing systems":
"Radiosonde balloons are manufactured from natural or synthetic rubbers. As the balloon ascends, it expands, eventually reaches the elastic limit for the material and explodes. Large scientific payloads are carried aloft on nonextensible balloons, usually made of polyethylene film. These balloons are partially filled on the ground. As the balloon ascends, the lifting gas expands to fill the available volume. A venting duct exhausts excess gas when the balloon is filled. the balloon floats at a constant altitude until a decrease in visible or infrared radiation cools the gas. The volume shrinks and the balloon descends to the ground unless ballast is dropped or the absorbed radiation increases. Sunset produces a 5 to ten percent loss in gas temperature, which must be offset by ballast release."
Lally also lists the following design considerations for balloons and payloads to lessen the balloon hazard to other aircraft:
Observations are made at as many as 27 pressure surfaces, including mandatory and significant levels.
The data collection instrument is a rawinsonde, containing sensors to measure temperature, pressure, humidity and wind direction and speed.
Transmitting and receiving electronics are typically included in the rawinsonde package, and the balloon may be tracked by direction finding instruments, radar systems or navigation aids.
Rawinsonde systems comprise pressure, temperature and humidity sensors. Winds are calculated based on ascent velocity and air density. Six variables, pressure, geopotential height, temperature, dewpoint depression, wind direction and wind speed are reported.
Versions of a radio direction-finding system operating at 1680 MHz with an automatic tracking system has been the standard sounding system used in the U. S. for over 30 years. Ground equipment is based on vacuum tube technology, flight equipment is solid-state circuitry. The system has a parabolic reflecting antenna with a mechanically scanned dipole on a centrally mounted pylon. Drive motors direct the antenna.
A time commutator transmits one complete set of sounding data (pressure, temperature, humidity and reference) once each second. Audio frequency containing temperature data is 35 Hz to 800 Hz, humidity data is transmitted at 35 Hz to 900 Hz. Pressure data is transmitted using a time commutation scheme, with audio signals for different pressures in a sequence that allows discrimination between increasing and decreasing pressures.