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Sunnyvale, CA | The biggest source of error in the GPS is the variability of the ionosphere. We are currently near the minimum of the 11.1 year solar sunspot cycle, with the new cycle to start sometime in the next 12 months. see www.spaceweather.com for more information on sunspots. the extra UV radiation that occurs from sunspots and solar flares causes the ionosphere to expand, which in turn changes the delay of a received GPS signal. DGPS corrections are designed to correct these ionosphere delays however, the corrections are not "perfect" and small errors will remain. So if you are looking at accuracy in December 2007, you will not have a full understanding of the DGPS errors in May of 2010 or 2011 or whenever the sunspot numbers are at the maximum. Since the current sunspot numbers are near zero, this is the best that GPS will behave until the end of the next cycle, in approximately 11 years, SF1 and WAAS have different networks of reference stations for creating the DGPS messages, and extrapolation of future accuracy includes a git of "guesswork." If you were to ask a GPS vendor what will happen to the accuracy of their DGPS receivers when the sunspots reach their maximum, you should expect an answer something like "we know DGPS will be less accurate than what it is now, and DGPS accuracy at the peak will depend upon the sunspot numbers at that time." | |
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SF1 vs. Waas
