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Results Obtained
A collection of CGS determined calibration results
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The calibration effort began in earnest when QuikSCAT was launched June, 1999. Since then calibration results have been obtained in numerous areas. Some of the major accomplishments are listed here:
Discovered a 1 second GPS / satellite timing error. When QuikSCAT was initially launched it received reference time incorrectly from Global Positioning Satellites (GPS). The time reported to the satellite was in error by one second. This error was not initially noticed because it corresponded to only a 7 km error on the ground, hardly noticeable on a global scale. However, when referenced to the CGS, a one second time error meant that the antenna was pointing 110 degrees away from the ground station, based on the knowledge that it takes 3.3 seconds for one antenna rotation. The error was quickly corrected.
Discovered a 1 second CGS timing error. The ground station, which also uses GPS for timing, had a 1 second timing error as well which was triggering data capture one second after the time it was referencing. Using ideas similar to those above, the erroneous times of CGS reception were discovered and subsequently corrected.
Verified a PRI of 5.3895 ms over the nominal 5.4 ms. The nominal pulse repetition increment is 5.4 ms. However, using the CGS to measure the time between pulses, a more accurate measurement of 5.3895 ms between pulses was determined.
Verified a pulse width of 1.49495 ms over the nominal 1.5 ms. By tuning the rectangular window used to find the pulses in the noise, it was found that the precise pulse width measurement was 1.49495 ms.
Verified 4 ms uncertainties in instrument timetags. Timetags are reported by the instrument every 100 pulses. They are only reported to the nearest millisecond. By using the difference between model and CGS data, it was discovered that the timetags are only accurate to 4 ms.
