Ceiling balloon

Japanese: シーリングバルーン（英語表記）ceiling balloon

A balloon used to measure the ceiling, or cloud base height. It is also called a cloud-sounding balloon. Generally, a small balloon is filled with hydrogen to give it buoyancy so that it will rise at a certain speed, and the time it takes for it to disappear into the clouds is measured. The speed of ascent v is determined by the buoyancy L and the weight W of the balloon, and is approximately related to v = k L ^1/2 /( W + L ) ^1/3 (where k is a coefficient determined by the shape and size of the balloon). If the speed of ascent is assumed to be constant, the height to the cloud base can be calculated.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

シーリング，すなわち雲底の高さを測定するための気球。測雲気球ともいう。一般には，小型気球に水素を充てんして所定の上昇速度が得られるよう浮力を与え，飛揚させてそれが雲の中で見えなくなるまでの時間を測定する。上昇速度vは，浮力Lと気球の重さWで決まり，近似的にv＝kL^1/2/(W＋L)^1/3(ただしkは気球の形と大きさで決まる係数)の関係が成立する。ここで上昇速度を一定とすれば，雲底までの高さが計算される。

出典　株式会社平凡社世界大百科事典第２版について　情報

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