Pilot-balloon observation

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pilot-balloon observation

(Commonly contracted pibal.) A method of winds-aloft observation, that is, the determination of wind speeds and directions in the atmosphere above a station.

This is done by reading the elevation and azimuth angles of a theodolite while visually tracking a pilot balloon. The ascension rate of the balloon is approximately determined by careful inflation to a given total lift. After release from the ground, periodic readings (usually at one-minute intervals) of elevation and azimuth angles of the balloon are recorded. These data are transferred to a winds- aloft plotting board, and the wind speed and direction at selected levels are calculated by trigonometric methods.
See graphing board, winds-aloft plotting board;
compare rabal, rawin, rawinsonde, double-theodolite observation.

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