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Airborne Geophysics and Precise Positioning Scientific Issues and Future Directions (1995) / Chapter Skim
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Appendix A: Effects of Selective Availibility (SA) and Antispoofing (AS)
Pages 79-84

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From page 79...
... (These results are obtained from the analysis of carrier phase measurements, and therefore nearly all of the RMS is due to dithering and natural drifts in the satellite and ground station clocks.) While the effects of SA are almost totally eliminated in differential positioning, the rapid fluctuations in the satellite clocks complicate the process of removing slips in the number of carrier phase cycles accumulated by the receiver.
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From page 80...
... These results were obtained using carrier phase measurements. The RMS range error for this interval is 0.25 m, and indicates that 1-m accuracy point positioning would be possible with existing satellites and receivers if SA was not on.
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From page 81...
... When a GPS receiver loses lock on a satellite, an arbitrary number of cycles of discontinuity in the carrier phase are introduced to the data. The postprocessing removal of cycle slips is complicated by the poorer-quality pseudorange data available under AS conditions.
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From page 82...
... 82 Airborne Geophysics and Precise Positioning 8.0 6.0 4.0 cry <, 2.0 0.0 .
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From page 83...
... The quantity plotted, the widelane, is a linear combination of L1 and L2 phase and range measurements that is independent of both geometry variations and the ionospheric delay. It is a direct measure of the difference in the number of cycles between the L1 and L2 phase measurements, and it is essential for rapid-static applications of GPS.
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Key Terms

  • carrier phase
  • range error
  • gps satellites
  • frequency standards
  • ionospheric delay

  • range measurements
  • data processing
  • automatic data
  • rms error
  • broadcast navigation

  • postprocessing removal
  • quantity plotted
  • gps signal
  • selective availability
  • satellite clocks

  • denies precise
  • gps tracking
  • careful analysis
  • ground station
  • gps frequency

  • scientific users
  • linear combination
  • precise millimeter
  • phase cycles
  • gps receivers

  • severely limits
  • precise ephemeris
  • global gps
  • removing slips
  • totally lost


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