From Wikipedia, the free encyclopedia

A bhangmeter is a type of photometer used on spy satellites that is intended to detect atmospheric nuclear detonations.^[1]

The first satellites which incorporated bhangmeters were the Advanced Vela satellites. An earlier generation of Vela satellites had been designed to detect nuclear explosions, but were not equipped with bhangmeters (they used X-ray sensors instead to detect an intense single pulse of X-rays).

The silicon photodiode sensors are designed to detect the distinctive bright double pulse of light that is emitted from atmospheric nuclear weapons explosions. This signature is a short and intense flash lasting around 1 millisecond, followed by a second much more prolonged and less intense emission of light taking a fraction of a second to several seconds to build up. The effect occurs because the surface of the early fireball is quickly overtaken by the expanding atmospheric shock wave composed of ionised gas. Although it emits a considerable amount of light itself, it is opaque and prevents the far brighter fireball from shining through. As the shock wave expands, the amount of light it emits increases with its surface area. The effect is unambiguous below about 30 km altitude, but above this height a more ambiguous single pulse is produced.

The name of the detector is a playful pun^[2], which was bestowed upon it by Fred Reines, one of the scientists working on the project. The name, deriving from the Indian word "bhang", is a variation of Indian cannabis which is smoked or drunk to induce the associated intoxicating effects – which a doubting scientist naming the device presumably must have thought someone must be under to believe the bhangmeter detectors would work properly. This is a contrast to the similarly-pronounced "bangmeter" one might associate with detection of nuclear explosions.^[3]

See also

• Vela Incident
• WC-135 Constant Phoenix

References