pilot balloon observation

Wiktionary

1. n. meteorology A method of winds-aloft observation, temperature, and relative humidity of the upper that is, the determination of wind speeds and air and to automatically transmit that directions in the atmosphere above a station. This is done by reading the elevation and azimuth angles of a theodolite (instrument) observation 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 wind speed and direction at selected levels are calculated by trigonometric methods.