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Green Satin radar
Green Satin was a doppler radar system developed by the Royal Air Force as an air navigation aid. The system provided direct measures of the drift speed and direction, and thereby allowed accurate calculation of the winds aloft. It was originally specified for the English Electric Canberra bomber, and subsequently used in a number of other aircraft, including much of the V bomber fleet. The name comes from an era when the Ministry of Supply used random combinations of colours and code words to prevent their code names being too literal. A version known as Blue Silk with lower top-speed limits was used in some marks of Canberra and by the Royal Navy..
==Background==
In air navigation there are six values of interest; airspeed, heading (the angle the nose is pointing), ground speed, course (or track), wind speed and wind direction. Using any four of these values and basic vector addition, the other values can be determined through the wind triangle. Once determined, the path of the aircraft can be accurately calculated using dead reckoning in comparison to an original fixed point.
Airspeed and heading can be measured with a fair degree of accuracy using onboard measurements, namely the airspeed indicator and gyrocompass. Since the aircraft flies within the air mass, it is not possible to directly measure wind values, so their determination must be carried out with reference to some external measure. For most of the history of air navigation, this was accomplished through a reverse dead reckoning process, timing the passage of objects on the ground to measure ground speed, and either estimating the drift or measuring it with simple optical instruments like the drift meter. Both are inherently inaccurate, with the US Navy suggesting such measures are accurate to only 10%.
Green Satin provided accurate and immediate measurements of the true ground speed and the drift angle. Combined with the airspeed and heading, air navigation complexity was greatly reduced. However, accurate dead reckoning also requires an accurate original "fix" from which future movements are determined. In practice, Gee would be used to take a fix after the aircraft reached cruise altitude and speed, and would be used to fine-tune the navigation until it passed out of Gee range, perhaps 300 to 450 nautical miles.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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