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 second interval processed using a double-difference strategy, using the day-to-day coordinate or phase residual autocorrelation determined with a 10 hour window leads to the steadiest estimates of the error-repeat lag, although a window as short as 2 hours 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 (23h 55m 54s), and removing these This is the authors' version of a manuscript that has been accepted by Journal of Geodesy. The final publication is available at Springer via doi:10.1007/s00190-006-0113-1 2 stacked residuals from the day in question (coordinate space), or by a similar method using double-difference 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 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.
Multipath is a major sidereally-repeating error affecting precise GPS positioning and deformation monitoring. Because satellite-receiver geometry repeats almost exactly every sidereal day, filtering can reduce multipath in near-static situations. Here, we investigate how sidereal filtering can be used in a switched multi-antenna array system providing semicontinuous GPS data, which may be adopted in order to reduce hardware costs.Depending on the receiver's set-up, the optimum session switching interval is 119 seconds or a multiple thereof. This provides sufficient reliable epochs using a short switching interval, and is synchronized with the appropriate geometry repeat interval for sidereal filter application. The semi-continuous sidereally-filtered GPS technique is efficient in detecting horizontal and vertical displacements, surpassing 5 mm and 8 mm precision respectively per epoch in near-static environments with moderately high multipath. This provides the capability of monitoring deformations occurring at periods greater than double the switching interval, although it can also be used for monitoring rapid structural deformations despite data gaps which may affect temporal resolution. Consequently, this combined method presents an efficient, cost-effective and precise GPS technique.
I. INTRODUCTIONGlobal Navigation Satellite System (GNSS) is an absolute positioning technique where the user receives transmitted data from at least four GNSS satellites to determine the position related to a fixed coordinate frame [1]. However, GNSS signals may be subjected to different error types that must be eliminated or
With the accelerated development of multi constellation Global Navigation Satellite Systems (GNSS), the field of satellite navigation is going through profound changes. Depending on a single constellation may not be sufficient to guarantee a successful positioning accuracy at any time. Consequently, having several constellations that can be used for positioning offers the opportunity to maintain continuous positioning. This became possible with the global coverage of other constellations such as (BeiDou, GLONASS, Galileo, and GPS). For engineering and scientific applications, this will present both opportunities and obstacles. This paper develops a 4-system positioning model for all the available observations from other GNSS and benefits from them. The important enhancement of satellite visibility, precision dilution, spatial geometry, accuracy, convergence, continuity, and reliability that combined use of multi-GNSS achieve to accurate positioning is attentively inspected and assessed, particularly in strained environments, overall, in the horizontal and 10 cm vertical components with precise orbits the multi-GSS PPP has a precise accuracy greater than 4 cm.
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