Bhangmeter
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A Bhangmeter is a type of optical detector used on satellites which are intended to detect atmospheric nuclear detonations.
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 worked based on the detection of the distinctive bright double pulse of light that is emitted from atmospheric nuclear weapons explosions.
The signature is actually 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, so 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 obviously a playful pun [1], which was apparently bestowed upon it by one or more scientists or engineers working on the project who were unconvinced of the feasibility of the optical detection approach of nuclear detonations. 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. Ironically, no bhangmeter was ever known to produce a false positive detection of a nuclear detonation throughout the entire time they were deployed on the Vela satellites.
