GPS sidereal filtering: coordinate- and carrier-phase-level strategies |
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Authors: | A E Ragheb P J Clarke S J Edwards |
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Institution: | (1) School of Civil Engineering and Geosciences, Newcastle University, Cassie Building, Newcastle upon Tyne, NE1 7RU, UK |
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Abstract: | Multipath error is considered one of the major errors affecting GPS observations. One can benefit from the repetition of satellite
geometry approximately every sidereal day, and apply filtering to help minimize this error. For GPS data at 1 s interval processed
using a double-difference strategy, using the day-to-day coordinate or carrier-phase residual autocorrelation determined with
a 10-h window leads to the steadiest estimates of the error-repeat lag, although a window as short as 2 h can produce an acceptable
value with > 97% of the optimal lag’s correlation. We conclude that although the lag may vary with time, such variation is
marginal and there is little advantage in using a satellite-specific or other time-varying lag in double-difference processing.
We filter the GPS data either by stacking a number of days of processed coordinate residuals using the optimum “sidereal”
lag (23 h 55 m 54 s), and removing these stacked residuals from the day in question (coordinate space), or by a similar method
using double-difference carrier-phase residuals (observational space). Either method results in more consistent and homogeneous
set of coordinates throughout the dataset compared with unfiltered processing. Coordinate stacking reduces geometry-related
repeating errors (mainly multipath) better than carrier-phase residual stacking, although the latter takes less processing
time to achieve final filtered coordinates. Thus, the optimal stacking method will depend on whether coordinate precision
or computational time is the over-riding criterion. |
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Keywords: | GPS Multipath Sidereal filter Autocorrelation Single epoch positioning |
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