noun
sounding balloon; sonde
Meteorological term for a balloon used to carry instruments aloft to measure atmospheric conditions.
気象庁は毎日、探測気球を飛ばして上空のデータを集めている。
The Japan Meteorological Agency launches sounding balloons every day to collect upper-air data.
Compound of 探測 (tansoku, 'sounding, probing') and 気球 (kikyū, 'balloon').