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 name s 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 ( " air direction " ) , ground speed , course ( " ground direction " , aka " 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 . Development . Green Satin started life in Operational Requirement ( OR ) 3015 in 1949 . This called for a device to provide an accurate measure of the groundspeed of an aircraft flying at any speed between 100 and 700 knots at all altitudes up to 60 , 000 feet . It also had to measure the drift angle up to 20 degrees on either side of the heading , with an accuracy of less than 0 . 1 degree . The solution to measuring ground speed was already well understood at the time , using a doppler radar system to compare the returned frequency of two or more signals . The difference in frequency is a direct measure of the speed of the aircraft . To measure the drift angle , Green Satin used an antenna with four feed horns arranged at slightly different angles . By rotating the antenna to each side of the aircraft and comparing the returns from each of the feed horns , a point would be found that maximized the frequency difference between them , at which point the antenna was aligned with the direction of motion . Green Satin was a pulsed system , although it was not a pulse - doppler radar in the typical meaning . The system did not attempt ranging measurements by pulse timing , it used pulses in order to allow it to use a single antenna for broadcast and reception . Frequencies were compared within a single pulse ( a monopulse radar ) , so the high frequency stability over longer multi - pulse times was not required . Green Satin was thus based on a simple cavity magnetron generator , rather than the more accurate traveling wave tube solutions like the klystron . The electronics were housed within two pressurized canisters ( some of which maintained their pressurization decades after being decommissioned ) mounted on large backplanes that included power supplies and various electrical connections . These were mounted above the cabin area on the rear bulkhead of the Canberra . Testing . In order to determine the operational accuracy of Green Satin , a lengthy series of test flights over land and water were carried out from an early Canberra . However , for these tests the G4B gyrocompass proved far too inaccurate as it required constant correction for drift . Additionally , Gee was accurate enough , but taking a fix required manual calculation by the operator . The test program demanded additional equipment to solve both of these problems . Accurate heading information was supplied by the Azimuth Datum Instrument ( ADI ) , a star tracker mounted on a periscope so that it projected its display on a plate in front of the navigator . Using angle measurements similar to those taken with a sextant , the aircraft heading could be accurately determined . For initial position fixes , Gee was replaced with the Decca Navigator System , which directly output measurements on three dials . By locating both the ADI and Decca output on the navigation console , along with the Green Satin outputs , a movie camera was able to record everything in real time for later data analysis on the ground . This consisted of taking a snapshot of the settings every six seconds and then averaging the instrument positions . Testing demonstrated that accuracy of Green Satin over land in straight and level flight was less than ±0 . 1 % of distance flown , and less than ±0 . 1 of a degree in drift . In use . The Green Satin was initially used with a simple display system with two large dials presenting true ground speed in knots on the left , and drift angle on the right . The output from this system was typically sent , along with the G4 compass ' output , to the Mark 4 Ground Position Indicator ( GPI ) . The GPI was a simple mechanical computer that integrated the inputs to produce an offset from a user - provided initial location ( taken from Gee , for instance ) , and presented this as either latitude and longitude or grid reference numbers on two odometer - like displays . Green Satin initially equipped the Canberra force , but was soon used on most larger RAF aircraft .